​What is quantum crystallography? [1]

Is it a hyped-up fad?

Is it “theory” or “experiment”?

What can it do? Is it useful?

Why has it become a new (perhaps better: reborn) IUCr commision?

The past

At the 2002 IUCr meeting in Geneva (rescheduled from Jerusalem) I was asked to speak after Jerome Karle, Nobel Laureate and one of those who had coined the term quantum crystallography (QCr) [2]. The room was packed, and soon there was a (second order?) phase change in the audience: either asleep or fidgeting. When Karle finished there was an immediate and astounding rush of people to leave. It was a bit disheartening for me; I had to shout over the commotion. Then there was more chaos, as some even turned back. I like to think it was because of me, but more likely it was defeat. I will review some of this 2002 material and show that QCr was in fact born with quantum mechanics itself [3]. I want to also highlight the work of Tibor Koritsanszky, recently lost to us, who together with Ewald medallist Philip Coppens brought about the “golden age” of our field [4].

The present

In a recent Australian Research Council grant application of mine assessor B lamented: “QCr is slowly creeping into crystallographic refinement to provide a better treatment of light i.e. hydrogen atoms … but how useful will it be in the vast majority of structural refinements?”. Even assessor D found it “hard to get excited about hydrogen atoms (sorry)”. Perhaps D is a physicist: only a non-chemist could be so callously unmoved by the proton, which forms the skin of all molecules, and is the fat positive partner of the beauteous electron! Surely these two are the hands of chemistry itself?! But I am actually rather pleased by that creeping comment: to me, it evokes a kind of desease-like inevitability: it resonates with the lack of direct funding [5]. In any case, I will explain why QCr is hard work, and I will review the impressive current progress by several groups.

The future

I think, except for Arthur C. Clarke, there have been no futorologist of note. Nevertheless, I will attempt to describe my vision for the use of model “experimental” wavefunctions to encode much more than just structral information; how QCr, the synthesis of quantum chemistry and crystallography will produce high quality databases worth mining; and how QCr has much to offer cognate fields like single-molecule and electron “diffraction”.

​[1] (a) Jayatilaka, D., N. C. (2012). Modern Charge-Density Analysis, edited by C. Gatti & P. Macchi, pp. 213-257. Springer.
(b) Grabowsky, S., Genoni, A., Buergi, H.-B. (2017). Chem. Sci. 8, 4159;
(c) Genoni, A.., et. al. (2018). Chem. Eur. J. 24, 10881. ​[2] Massa, L., Huang, L., Karle, J. (1995). Int. J. Quantum Chem. 56, 371. ​[3] James, R.W., Waller, I., Hartree, D.R. (1928) Proc. Royal Soc. London Ser. A 118, 334

[4] Koritsanszky, T.S., Coppens, P. (2001). Chem. Rev. 101, 1583

​[5] Take heart east-coast scientists! Research can continue, even in Western Australia where, to paraphrase W. Pauli and P. Doherty, we are not even of the Pacific bogan variety, https://tinyurl.com/jmv6uyne .

Due to the ever-increasing demands on the materials with enhanced properties, the task of searching for them using atomistic modeling methods is becoming increasingly important. The problem of designing novel materials comes down to finding a global minimum in a very noisy landscape in a multi-dimensional space (potential energy surface). This problem can be solved using several methods, yet the USPEX [1,2,3] evolutionary algorithm proved its effectiveness. The USPEX limitations are calculation at zero temperatures and small number of atoms in the unit cell, since the calculation of the energy of the structures (and their selection) takes place within the framework of the density functional theory (DFT). Here we present a new method (T-USPEX) which is capable of finding stable structures at finite temperatures and pressures.

T-USPEX is based on the previously developed evolutionary algorithm USPEX. The main differences come from crystal structure relaxation at finite temperature and from the way of fitness function calculation (in this case – Gibbs free energy). Relaxation part is done using molecular dynamics in the NPT ensemble with pressure corrections taken into account. Gibbs free energy is calculated using thermodynamic integration with the corrections from thermodynamic perturbation theory. For these methods a big supercell is needed, so MTP [4] machine learning interatomic potentials is used. In this talk results for high-temperature phases of Al, Fe, Ti, U and MgSiO₃ will be presented.

Acknowledgments: This work was supported by RFBR foundation № 19-73-00237.

[1] C. W. Glass, A. R. Oganov, and N. Hansen, Comput. Phys. Commun. 175, 713 (2006).

[2] A. R. Oganov, A. O. Lyakhov, and M. Valle, Acc. Chem. Res. 44, 227 (2011)

[3] A. O. Lyakhov, A. R. Oganov, H. T. Stokes, and Q. Zhu, Comput. Phys. Commun. 184, 1172 (2013).

[4] A. V. Shapeev, Multiscale Model. Simul. 14, 1153 (2016)

The design of molecular crystals with targeted properties is the goal of crystal engineering. However, our predictive understanding of how a crystal’s properties relate to its structure, and how crystal structure in turn relates to molecular structure, are not yet sufficiently reliable to confidently design functional materials. Computational methods for crystal structure prediction (CSP) have been developed to help anticipate the crystal structure that a molecule will form. These methods are based on a global search of the lattice energy surface and a ranking of local energy minima according to their calculated relative stabilities. Thus, each molecule is associated with a list of potential crystal structures, each of which then leads to a set of predicted properties. The resulting ensemble of structures, their relative energies and associated properties can be interpreted to judge a molecule's promise for a target function. These methods have been demonstrated to be valuable in guiding experimental materials discovery programmes. A remaining challenge is the best choice of molecules that should be assessed, given the enormous chemical space of possible molecules. To address this, we have combined evolutionary searching of chemical space with large scale crystal structure and property prediction as a route to the discovery of novel molecules with high likelihood of yielding good properties [1]. The approach will be discussed with example studies in the area of organic semiconductor discovery.

[1] Cheng, C. Y., Campbell, J. E. and Day, G. M. (2020) Chem. Sci.,11, 4922-4933

Metal-organic frameworks (MOFs) are microporous materials with many exciting applications, such as gas storage and separation, catalysis, platforms for artificial photosynthesis and energetic materials. The wide range of applications is strictly related to the modular node-and-linker composition, where different combinations of building blocks yield materials with various properties. The presence of a vast number of combinations for different node and linker, however, poses a real challenge for the experimental MOF design.

An ab initio crystal structure prediction (CSP) method for MOFs has been reported by our group recently, and the method is based on the ab initio random structure searching (AIRSS) [1] and Wyckoff Alignment of Molecules (WAM) [2] algorithms. In this publication, a wide range of existing MOF structures have been investigated. Herein, we will demonstrate the first examples for the prediction of new MOF materials from metal azolate framework (MAF) and hexafluorosilicate families using our CSP method, combined with experimental mechanochemical synthesis and crystal structure determination. The solvent-free mechanochemical synthesis guided by theoretical structure prediction provides for an efficient and green approach to MOF design.

The concept of MOF design goes beyond just the prediction of crystal structures. The connections between the crystal structures and chemical reactivity of freshly designed MOFs will also be studied by utilizing periodic density functional theory (DFT). Furthermore, our theory-based MOF structure and property predictions will be validated experimentally via mechanochemical screening and thermal studies, and ultimately aiming to improve our understanding of MOFs.

[1] Pickard, C. J.; Needs, R. J. (2011). J. Phys. Condens. Matter 23, 53201.

[2] Darby, J. P.; Arhangelskis, M.; Katsenis, A. D.; Marrett, J. M.; Friščić, T.; Morris, (2020). Chem. Mater. 32, 5835–5844.

Autonomous materials discovery with desired properties is one of the ultimate goals for materials science [1]. In this work, we have developed constrained crystal deep convolutional generative adversarial networks (CCDCGAN, Figure 1(a)) based on a proper construction of the latent space [2], which can predict stable crystal structures. In particular, physical properties can be optimized in the latent space, where the formation energy is considered in the current model so that stable structures are predicted directly. We have successfully applied the approach on a randomly chosen binary Bi-Se system and observed that most known phases can be validated with quite a few distinct structures predicted [3]. Furthermore, trained using more than 50,000 compounds in the Materials Project database, we recently extended the algorithm to multicomponent systems coving most elements in the periodic table. As shown in Figure 1(b), two novel structures can be obtained for the Cd-Li system. Detailed analysis reveals that the approach can be used to predict novel crystal structures for various materials systems, and the generation efficiency can be further improved by considering a larger training set. It is expected that the other physical properties (such as band gaps) can be optimized in the latent space as well, giving us the chance to perform multi-objective optimization in the future.

Design of new types of metal-organic frameworks (MOFs), the microporous materials with a wide range of functional properties, is an active area of materials research. The vast variety of available linker and node combinations leads to an incredible variety of potential MOF structures, providing an opportunity for tailoring the functional properties and thermodynamic stability of the new materials. At the same time, navigating the vast structural space of putative MOFs is proving to be a challenge for experimental screening, that can benefit from the guidance provided by computational chemistry methods. In this presentation we will describe the application of periodic density-functional theory (DFT) calculations together with state-of-the-art ab initio crystal structure prediction (CSP) calculations in elucidating the structural aspects of MOF thermodynamic stability and performing computational property-driven design of new MOFs.

The presentation will commence with a theoretical study of the systematic effects of linker substituents on the thermodynamic stability of a series of isostructural zeolitic imidazolate frameworks (ZIFs) with sodalite topology.[1] We will show how periodic density functional theory (DFT) calculations offer highly accurate predictions for the thermodynamic stability of the ZIF structures as a function of linker substitution, also taking into account the effects of crystal packing of pure ligands. The accuracy of periodic DFT calculations will be backed up by the excellent correlation with the experimental solution calorimetry measurements. Moreover, it will be demonstrated how simple descriptors, such as Hammett σ-constants and electrostatic surface potentials (ESPs) offer convenient tools for rapid pre-screening of linker substituents, before performing a more in-depth computational analysis.

We will continue with a demonstration of our recently-developed method for ab initio CSP, which uses the Wyckoff Alignment of Molecules (WAM) procedure to predict the structures of new MOFs, with improved computational efficiency enabled through careful consideration of molecular and crystallographic symmetry.[2] We will demonstrate the use of our CSP approach for predicting polymorphism, thermodynamic stability, porosity and optical properties of new MOFs in a series of computational studies backed up by experiment. It will also be shown how MOF CSP can be used as a tool to elucidate the crystal structures of poorly-crystalline MOFs, which are difficult to determine with X-ray diffraction methods.

[1] Novendra, N., Marrett, J. M., Katsenis, A. D., Titi, H. M., Arhangelskis, M., Friščić, T. & Navrotsky, A. J. (2020). J. Am. Chem. Soc. 142, 21720.

[2] Darby, J. P., Arhangelskis, M., Katsenis, A. D., Marrett, J. M., Friščić, T. & Morris, A. J. (2020). Chem. Mater. 32, 5835.

Hydrogen-rich hydrides attract great attention due to recent theoretical [1] and then experimental discovery of record high-temperature superconductivity in H₃S (T_C = 203 K at 155 GPa [2]).

Here we perform a systematic evolutionary search for new phases in the Fe-H [3], Th-H [4], U-H [5] and other numerous systems under pressure [6] in order to predict new materials which are unique high-temperature superconductors.

We predict new hydride phases at various pressures using the variable-composition search as implemented in evolutionary algorithm USPEX [7-9]. Among the Fe-H system two potentially high-T_C FeH₅ and FeH₆ phases in the pressure range from 150 to 300 GPa were predicted and were found to be superconducting within Bardeen-Cooper-Schrieffer theory, with T_C values of up to 46 K. Several new thorium hydrides were predicted to be stable under pressure using evolutionary algorithm USPEX, including ThH₃, Th₃H₁₀, ThH₄, ThH₆, ThH₇ and ThH₁₀. ThH₁₀ was found to be the highest-temperature superconductor with T_C in the range 221-305 K at 100 GPa. Actinide hydrides show, i.e. AcH₁₆ was predicted to be stable at 110 GPa with T_C of 241 K.

To continue this theoretical study, we performed an experimental synthesis of Th-H phases at high-pressures including ThH₁₀. Obteined results can be found in Ref. [10].

Acknowledgments: This work was supported by RFBR foundation № 19-03-00100 and facie foundation, grant UMNIK №13408GU/2018.

[1] D. Duan et al., Sci. Rep. 2018, 4, 6968.

[2] A.P. Drozdov et al. Nature. 2015, 525, 73–76.

[3] A.G. Kvashnin at al. J. Phys. Chem. C 2018, 122 4731-4736.

[4] A.G. Kvashnin et al. ACS Applied Materials & Interfaces 2018, 10, 43809–43816.

[5] I.A. Kruglov et al. Sci. Adv. 2018, 4, eaat9776.

[6] D.V. Semenok et al. J. Phys. Chem. Lett. 2018, 8, 1920-1926.

[7] A.O. Lyakhov et al. Comp. Phys. Comm. 2013, 184, 1172-1182.

[8] A.R. Oganov et al. J. Chem. Phys. 2006, 124, 244704.

[9] A.R. Oganov et al. Acc. Chem. Res. 2011, 44 227-237.

[10] D.V. Semenok et al. 2019, Mat. Today.

The Protein Data Bank (PDB) was established in 1971 as the first open-access digital data resource in biology with just seven X-ray structures of proteins. During its first 50 years of continuous operations, PDB holdings have grown to more than 175,000 structures becoming the single global archive of 3D-structures of proteins, nucleic acid, and their complexes with one another and small-molecule ligands. Open access to expertly biocurated PDB structures enables the efforts of many millions of basic and applied researchers, educators, and students around the world. Their work impacts fundamental biology, biomedicine, bioengineering, biotechnology, and energy sciences.

The Worldwide Protein Data Bank (wwPDB, wwpdb.org) manages the PDB archive according to the FACT principles of Fairness-Accuracy-Confidentiality-Transparency and the FAIR principles of Findable-Accessible-Interoperable-Reusable. Current wwPDB members include the US RCSB Protein Data Bank (RCSB PDB), Protein Data Bank in Europe (PDBe), Protein Data Bank Japan (PDBj), Electron Microscopy Data Bank (EMDB), and Biological Magnetic Resonance Bank (BMRB).

All data in the PDB archive conform to the wwPDB PDBx/mmCIF data dictionary, which is fully extensible both human- and machine-readable. PDB structures are composed of amino acids or nucleotide building blocks that comprise biopolymers, and associated small molecules such as water molecules, solute molecules, ions, co-factors, metabolites, enzyme inhibitors, drugs, etc. Every new structure coming into the PDB is processed using the wwPDB OneDep global system for deposition, validation, and biocuration. All PDB structures are accompanied by an official wwPDB Validation Report, exemplifying standards developed collaboratively with wwPDB Task Forces composed of community experts.

Small-molecule constituents of PDB structures are defined in the wwPDB Chemical Component Dictionary (CCD). This dictionary contains detailed chemical descriptions for standard and modified amino acids/nucleotides, small molecule ligands, solvent molecules, and others. Precise knowledge of interactions between macromolecules and small-molecule ligands is central to our understanding of biological and biochemical function, drug action, mechanisms of drug resistance, and drug-drug interactions.

Recent enhancements to the CCD and the wwPDB Validation Report will be described, together with value-added information concerning ligand quality now available on the US Research Collaboratory for Structural Bioinformatics Protein Data Bank PDB website (RCSB PDB, RCSB.org).

wwPDB members are US RCSB PDB (supported by NSF, NIH, DOE, and Rutgers Cancer Institute of New Jersey), PDBe (EMBL-EBI, Wellcome Trust, BBSRC, MRC, and EU), and PDBj (NBDC-JST), and BMRB (NIGMS).

Peer review of supporting data for submitted research articles is currently assuming great significance in scientific publishing, but is not new for the journals of the IUCr. Co-editors of Acta Crystallographica C under the editorship of Sidney Abrahams (1924-2021) were expected to validate the consistency of crystal structure data for reported structures, for which cell parameters and symmery, coordinates, geometry and anisotropic displacement parameters were mandatory. The journal developed software to reduce the calculational burden, and this evolved into the checkCIF service that allowed authors to participate in the validation effort, and to account for apparent anomalies or outliers in their derived structures. An early consequence was the almost complete elimination of corrigenda that resulted from post-publication surveys by individual scientists or by database aggregators. Over the years checkCIF increased in sophistication and power (authors were required to supply structure factors in machine-readable form), and has been adopted by other journal publishers and by structural databases. The IUCr Diffraction Data Deposition Working Group (2011-2017) emphasised the value of access to raw experimental data in evaluating structure interpretation, and IUCr Journals have responded by encouraging authors to make available their diffraction data sets. The journals continue to explore ways to improve the refereeing process with regard to data, in their effort to make the initial publication of the version of record of an article as error-free as possible.

The Cambridge Structural Database (CSD) was founded on a vision that collective use of data would lead to the discovery of new knowledge which transcends the results of individual experiments. Excellent data sharing practices in the crystallographic community as well as deposition and curation processes at the CCDC have enabled that vision to come to true.

This talk will demonstrate a number of ways in which a structural database such as the CSD can work with the community to help set standards from validation to publication and explore what part we play in the pre and post publication peer review of crystallographic data. We will share our experiences evolving our interactive deposition service, from the integration of checkCIF, to the establishment of links to raw diffraction data. We will also look at how repositories can support the peer review of data and what impact an increase of data published solely through the CSD might have. The presentation will conclude by looking at how reviewing crystallographic results might change in the future, how the CSD could evolve and how we can better help the community increase the integrity of data that is shared.

High-resolution macromolecular structures determined using crystallography, NMR, and cryo-EM provide a gold standard for evaluation of important properties of biomolecules, but the quality of some structures, as well of their presentation, is not always fully acceptable. Whereas quality checking tools provided by the PDB during deposition process may flag some common problems, the resulting red flags are not always addressed by deposition authors. Some journals require that manuscripts be accompanied by validation reports in order to assist reviewers in evaluation of the validity of presented structures, whereas other journals do not have such requirements. Additionally, validation reports are more helpful in identifying global problems, while some local problems may not be apparent. Utilization of additional tools and interactive software might assist readers in making the best use of published structural data. Using examples extracted from the Protein Data Bank, as well as from journal publications, some common problems will be identified and suggestions will be made on how to avoid their reoccurrence.

Over the last decades, the PDB has been developing tools and standards for the assessment of the quality of the structural models deposited in its archives. Similarly, more and more journals are now requiring validation reports generated by the PDB as a prerequisite for manuscript submission. Such quality metrics have been used previously to gauge the relationship between structural model quality and publication venues [1,2]. More recently, these indicators have been applied to assess the evolution of the quality of the PDB deposits with time [3] using the concept of a percentile (P_Q1) metric, which combines such measures as R_free, RSRZ (normalized Real Space R-factor) outliers, Ramachandran outliers, Rotamer outliers, and Clashscore.

In this paper we will show how the quality of macromolecular models deposited in the PDB has changed over the years (Fig. 1) and how the P_Q1 parameter can be converted to a new measure, P_Q1(t,d), that takes into account time (t) and data resolution (d). The proposed new measure can be used to reveal how structure quality in a given moment of time was related to such issues as:

• differences between proteins and nucleic acids;
• comparison with structural genomics projects;
• assessment of deposits without journal publications (To be published);
• journal impact factor (Fig. 2).

The paper will also discuss how the quality of crystallographic macromolecular structures in the PDB has improved over the last years and highlight some crucial periods in this history.

[1] Brown, E. N. & Ramaswamy, S. (2007). Acta Cryst. D63, 941–950.

[2] Read, R. J. & Kleywegt, G. J. (2009). Acta Cryst. D65, 140–147.

[3] Shao, C., Yang H., Westbrook, J. D., Young, J. Y., Zardecki, C. & Burley, S. K. (2017). Structure 25, 458–468.

Since the discovery of quasicrystals in the early 1980s, the diffraction of aperiodically ordered structures has been a fruitful area of research in mathematical crystallography and, increasingly, in mathematics. The characterisation of the diffraction of a structure is closely linked to the question of how to define a crystal, and indeed how to define the concept of order in general. For the purpose of this talk, I shall adopt a rather general perspective, in the sense that I shall consider mainly pure-point diffractive systems, but also talk about systems with singular continuous or absolutely continuous diffraction. While some of these systems may not be realised in nature, they are increasingly of interest as metamaterials, with the intention to obtain materials with purpose-made properties.

In this talk, I shall present an overview on the current state of knowledge on the diffraction of aperiodic structures. Because the mathematics behind some of the results is non-trivial, I shall try to motivate and explain the results by means of explicit example systems, using some rather familiar as well as some less familiar examples to demonstrate what can happen.

This includes, on the one hand, examples of cut-and-project sets, which are aperiodic structures obtained by projection of part of a higher-dimensional lattice. For such systems, which include familar examples such as the one-dimensional Fibonacci system or planar Penrose tilings, the theory of diffraction is rather well understood. On the other hand, there are self-similar structures that are obtained by an (iterative) inflation procedure, for which diffraction is, in general, much less well understood. For the latter, recent work on using a renormalisation-type approach, which exploits the self-similarity, provides some new insight. Particularly interesting examples are systems which possess a description as a projection set as well as an inflation symmetry, and I shall finish with the discussion of a class of examples of such structures, which is based on a two-dimensional Fibonacci system.

Electron diffraction is gradually becoming a broadly accepted alternative structure determination method to the established approaches like single crystal x-ray diffraction. Although electron diffraction was used for structure determination long time ago, the real breakthrough was obtained only thanks to the rapid development of the three-dimensional electron diffraction methods (3D ED). Several 3D ED experimental techniques exist, but they all share the basic principle of collecting three-dimensional diffraction information from a single very small crystal by tilting the crystal, continuously or in steps, and recording the diffraction patterns as the crystal is tilted [1].

In the early days of 3D ED, mostly inorganic materials were analysed, as these materials are less beam sensitive and therefore easier to measure. Nevertheless, soon first successful attempts to analyse organic materials appeared (reference). Gradually, over the past ten years, structure analysis of organic materials by 3D ED has become almost a routine technique.

Structure analysis of molecular materials by 3D ED has certain specifics. First, molecular crystals are, typically, much more beam sensitive than crystals of inorganic materials, although this rule is by far not strictly applicable. The beam sensitivity of organic materials calls for specific experimental techniques. These include: measurements at low-temperature conditions (usually cooling to liquid nitrogen temperatures) to limit the beam damage; use of modern direct electron detectors with low background and high sensitivity to maximize the signal-to-noise ratio; combination of partial data sets from several crystals; or application of serial diffraction techniques. The latter can include either scanning a large single crystal with a small probe, measuring each diffraction pattern on a fresh part of the crystal [2,3], or collecting single diffraction patterns from a large number of crystals and combining them in a manner similar to serial femtosecond crystallography [4].

Once suitable data are collected, the challenge continues in the structure analysis part. It is usually not complicated to solve the structure by ab initio structure solution methods. However, it is challenging to obtain a good quality refinement. The multiple scattering effects that are always present in electron diffraction break the kinematical nature of the diffraction. If the kinematical approximation is used in the refinement, the figures of merit of the refinement tend to be high and weak signals in the structure may be obscured. This makes, for example, the detection of hydrogen atoms difficult, although not impossible [5,6]. The fit to experimental data can be improved by employing the dynamical diffraction theory in the calculation of the model intensities [3, 6, 7]. Such calculation results in an improved fit to experimental data and, as a consequence, to higher accuracy of the refined parameters and better sensitivity to weak features. A very important advantage of using the dynamical diffraction theory in the refinement is the possibility to determine the absolute structure of the crystals [3].

Despite of al the challenges, 3D ED was already proved to be an extremely successful technique for structure determination of molecular crystals. The fact that it can routinely analyse crystals with sub-micrometre size makes it an attractive alternative to single crystal x-ray diffraction.

[1] Gemmi, M., Mugnaioli, E., Gorelik, T. E., Kolb, U., Palatinus, L., Boullay, P., Hovmöller, S., Abrahams J. P. (2019). ACS Cent. Sci. 5, 1315.

[2] Kolb, u., Mugnaioli, E., Gorelik, T. (2011). Cryst. Res. Technol. 46, 542.

[3] Brázda, P., Palatinus, L., Babor, M. (2019). Science 364, 667

[4] Smeets, S., Zou, X., Wan, W. (2018). J Appl Cryst. 51, 1262.

[5] Jones, C. G., Martynowycz, M. W., Hattne,, J. Fulton,T. J., Stoltz, B. M., Rodriguez, J. A., Nelson, H. M., Gonen, T. (2018). ACS Cent Sci. 4, 1587.

[6] Palatinus, L., Brázda, P, Boullay, P., Perez, O., Klementová, M., Petit, S., Eigner, V., Zaarour, M, Mintova, S. (2017). Science 355, 166.

[7] Palatinus, L., Petricek, V., Correa, C. A. (2015). Acta Cryst. A 71, 235.

This work was funded by the Czech Science Foundation, project number 21-05926X.

In order to understand the packing and orientation of organic semiconductor thin films, we make use of microcrystal electron diffraction (MicroED) and grazing-incidence wide-angle X-ray scattering (GIWAXS). These complementary techniques provide structural insights to the structure of these thin films and can be used with the same sample preparation methods that are used to create the functional films. This removes the need for time-consuming crystallization experiments that may not directly capture the same semiconductor structure found in the films. We will present the application of these methods on four organic semiconductor samples, some of which represent novel structures determined by MicroED.

Three-dimensional electron diffraction (3D ED) has matured into a method routinely employed by several worldwide-located laboratories for addressing crystallographic problems, which were considered intractable by X-ray diffraction [1]. The main advantage of ED is the ability to get diffraction data from volumes of few hundreds or even few tens of nanometers. This allows acquiring comprehensive 3D structural information from crystals too small for X-ray single-crystal methods, from coherent domains in pervasively twinned or disordered materials, from isolated domains embedded in inorganic or biological matrices and from minor constituents of powdered polyphasic mixtures.

From the beginning, the main shortcomings of 3D ED appeared connected with the deterioration of the sample induced by TEM vacuum or by beam damage. Moreover, organic crystals are typically affected by mosaicity and bending. In this contribution we will show different experimental protocols for data collection and analysis that can be employed in any experimental set-up, even for low-voltage TEMs. Beam damage is minimised by coupling STEM imaging for sample search and tracking, and a small-size low-intensity parallel electron beam for diffraction data acquisition [2]. The size of the beam is crucial for picking narrow areas of the sample, either when coherent crystal domains are very small or when there is a need for moving to fresh parts of the crystal in order to lessen beam damage effects.

According with the specific sample characteristics, 3D ED data acquisition can be performed in step-wise mode, coupled with beam precession [3], or by continuous rotation [4]. Both approaches strongly benefit by the disposal of a new-generation ultra-fast single-electron detector [5]. Moreover, background noise can be almost completely suppressed with an energy filter that cuts out the inelastic scattering. Structure solution is normally obtained ab-initio by direct methods. Still, global optimisation approaches, like simulated annealing [6], are valuable alternatives when data are affected by low resolution, preferential orientation or experimental errors that compromise the overall intensity reliability (e.g. beam damage, merohedric twinning, diffuse scattering).

We will thus discuss examples of recently published [7, 8] and forthcoming structure characterizations of pharmaceutical compounds, organic charge-transfer co-crystals and polycyclic aromatic hydrocarbons. For each case, specific problematics of the sample will be discussed, together with experimental solutions adopted for achieving structural solution and refinement.

[1] Gemmi, M., Mugnaioli, E., Gorelik, T. E., Kolb, U., Palatinus, L., Boullay, P., Hovmöller, S. & Abrahams, J. P. (2019). ACS Cent. Sci. 5, 1315.

[2] Kolb, U., Gorelik, T., Kübel, C., Otten, M. T. & Hubert, D. (2007). Ultramicroscopy 107, 507.

[3] Lanza, A., Margheritis, E., Mugnaioli, E., Cappello, V., Garau, G. & Gemmi, M. (2019). IUCrJ 6, 178.

[4] Gemmi, M. & Lanza, A. E. (2019). Acta Cryst. B75, 495.

[5] van Genderen, E., Clabbers, M. T. B., Das, P. P., Stewart, A., Nederlof, I., Barentsen, K. C., Portillo, Q., Pannu, N. S., Nicolopoulos, S., Gruene, T. & Abrahams, J. P. (2016). Acta Cryst. A72, 236.

[6] Burla, M. C., Caliandro, R., Carrozzini, B., Cascarano, G. L., Cuocci, C., Giacovazzo, C., Mallamo, M., Mazzone, A. & Polidori, G. (2015). J. Appl. Cryst. 48, 306.

[7] Andrusenko, I., Hamilton, V., Mugnaioli, E., Lanza, A., Hall, C., Potticary, J., Hall, S. R. & Gemmi, M. (2019). Angew. Chem. Int. Ed. 58, 10919.

[8] Das, P. P., Andrusenko, I., Mugnaioli, E., Kaduk, J. A., Nicolopoulos, S., Gemmi, M., Boaz, N. C., Gindhart, A M. & Blaton, T., (2021). Cryst. Growth Des. 21, 2019.

3D Electron Diffraction (3D ED) has reached a point where it has become a routine technique for single-crystal diffraction studies at the nanometre scale [1]. Recently, some acquisition softwares have been developed with the aim of automatization and universal application [2]. One of them is the Fast and Automated Diffraction Tomography (Fast-ADT) [3]. This acquisition module is based on two tilt scans of the goniometric stage over the desired tilt range; the first one to monitor the crystal displacement with respect to the tilt angle in order to interpolate the necessary electron beam shifts, and the second one to acquire the diffraction patterns while following the crystal automatically. This procedure allows reliable diffraction acquisitions for crystals down to 20 nm provided that the stage has been aligned for tomography experiments and the holder is kept in good mechanical conditions. Fast-ADT can work in both TEM and STEM mode, but STEM is preferred mainly because of its low dose to acquire scanned images and its clear visualization of tiny or layered crystals in such conditions [4]. Another difference to other 3D ED routines is the use of Nano-Beam Electron Diffraction (NBED) instead of selected area electron diffraction. The combination of Fast-ADT and NBED enables several approaches focused on the optimization of 3D ED experiments, such as the shift of the beam at different positions of the same crystal or different crystals during diffraction pattern acquisitions. This versatility is beneficial as it gives the needed flexibility to study beam sensitive specimens even with post TEM column charged-coupled devices.

As an example, Fast-ADT was used to acquire datasets from disperse red 1 (DRED1) crystals, an organic molecule that was recrystallized in toluene. The dye DRED1 is an azobenzene derivate, which are well known for their photochromatic properties and large optical and electro-optic properties in various polymeric films. The processing of six Fast-ADT datasets­­­­­­­­­­ with eADT [5] revealed a triclinic crystal system with unit-cell parameters of a = 7.72 Å, b = 11.14 Å, c = 19.58 Å, α = 73.8°, β = 83.0°, γ = 70.5° and V = 1523.5 ų and indicated four molecules per unit cell. The real space method simulated annealing, implemented in Sir2014 [6], was used to solve the structure and the positions of the azobenzenes were found using both P1 (Z = 4) and P-1 (Z’ = 2). The small difference between structure solutions performed in both space groups was taken as an indication that the crystal structure could be described in the centrosymmetric space group. However, the correct orientation of the flexible side chains was more difficult to retrieve because of their high degree of freedom. For this reason, on one hand, two datasets were merged to obtain a higher number of independent reflections (85%) and, on the other hand, an analytical description of the rocking curves was applied to enable a frame orientation refinement and an improved reflection intensity integration [7]. These processing tools allowed solving the new polymorph of DRED1 ab initio in P-1, directly revealing the 46 non-hydrogen independent atoms from the scattering density map. Finally, the structure model was refined based on X-ray powder diffraction data using the Rietveld method.

Electron diffraction makes it possible to obtain crystal structures at atomic resolutions, for both small and macro-molecules [1-2]. For this purpose, the same as in case of X-ray diffraction, it is necessary to use scattering factors model. After years of experience people learned that Independent Atom Model (IAM) is not the best choice for X-ray diffraction. It is not a surprise that also for electron diffraction it will not give the best results. Different aspherical models, already known for X-ray diffraction, can be implemented for electron diffraction. However, it is necessary to investigate their possibilities and limits, to verify correctness of obtained structures.

We present analysis of refinements of Transferable Aspherical Atom Model (TAAM) with parameters of multipolar model taken from MATTS databank (databank of Multipolar Atom Types from Theory and Statistical clustering) - successor of UBDB databank [3]. We used electron scattering factors implemented in DiSCaMB library[4] and interfaced with Olex2-1.3[5]. Such solution is available through .tsc files [6] and it requires little effort (Fig.1).

Numerous refinements were performed against experimental electron structure factors and theoretical electron structure factors so as to find optimum refinement strategy. We discuss, inter alia, possibility of refinement of atomic displacement parameters, both for hydrogen and non-hydrogen atoms or positions of hydrogen atoms. It is interesting how they change e.g. with resolution cut-off. To confirm that our conclusions could be transferred for different, but still organic structures, we made simulations for several pharmaceutical compounds, such as carbamazepine, paracetamol, 1-methyluracil.

Support of this work by the National Centre of Science (Poland) through grant OPUS No.UMO-2017/27/B/ST4/02721 and PL-Grid through grant ubdb2019 are gratefully acknowledged.

Electrons interact with matter 10⁶ times stronger than X-rays do, which makes it an ideal radiation source for diffraction and imaging experiments on submicron- and nano-sized crystals. During the last three decades, 3D electron diffraction (3D ED) has been developed into a regular and reliable technique for structure determination, which is complementary to single-crystal X-ray diffraction (SCXD) and single particle analysis. One issue for electron diffraction is inelastic scattering, which brings background in the diffraction patterns. This background is most obvious for electron diffraction patterns from protein crystals, especially at low angles. Even though modern diffraction data software (XDS, DIALS, MOSFLM) has sophisticated background removal algorithms to deal with this, the existence of inelastic scattering will still add errors in the diffraction experiment. The inelastically scattered electrons can be removed by energy filters. Here, we implemented energy-filtered 3D ED using a Gatan Energy Filter (GIF) in both TEM selected area electron diffraction mode and STEM micro/nanoprobe mode. We explained the setup in detail and this implementation can allow researcher to have better accessibility to energy-filtered 3DED experiments because more microscopes are equipped with a GIF than an in-column omega filter. We also proposed a crystal tracking method in STEM mode using live HAADF image stream. This method enables us to collect energy-filtered 3DED datasets in STEM mode with a larger tilt range without foregoing any frames. This can avoid crystal moving out of the beam during the tilting and the tilt range can always reach the maximum tilt range of the microscope (in our case ~150°). We acquired multiple datasets from different crystals and we further processed and refined the structures. We observed that the final R₁ will improve 20% to 30% for energy-filtered datasets compared with unfiltered datasets. We also discussed the possible reasons that lead to the improvement.

3D Electron Diffraction (3D ED) is a very powerful tool for the structural elucidation of nanocrystalline particles. After its Science nomination for “Breakthrough of the year 2018” [1], 3D ED, using the continuous rotation method [2-3], and well-established crystallographic software, is gaining a lot of attention in all areas of research. In the recent years, many achievements using electron diffraction techniques have been made in the fields of organic and inorganic molecules, polymorphism, geological sciences, natural products, biomolecules, material sciences, energetic materials, batteries, and many others [2-4]. Such experiments are currently done in a (modified) transmission electron microscope, thus requiring customized experimental and data-analysis protocols, which vary depending on each specific instrumental setup. Hence, 3D ED experiments are currently carried out only by specialized staff and require a remarkable investment in terms of time, expertise, knowhow transfer and resources.

A strong need has emerged in the crystallographic community for instrumentation specifically dedicated to 3D ED experiments.

Here we present an electron diffractometer: a new device developed and optimized exclusively for 3D ED which allows a time-effective, automated and standardized experimental workflow along with user-friendly operability. Furthermore, the electron diffractometer is conceived to make use exclusively of well-established crystallographic approaches and to interact seamlessly with readily available crystallographic software. Experimental examples of different kind of materials measured with this device will be showcased.

In scanning transmission electron microscopy (STEM), real space image quantification allows the counting of the number of atoms in a crystallographic projection, perpendicular to the electron probe. Atom counting is an established method in high-angle annular dark-field (HAADF) imaging and has applications that include the estimation of 3D shapes in metallic nanoparticles [1-2], or local composition variations in high-Z materials with known, constant thickness [3]. The incoherent nature of the HAADF contrast yields a monotonic increase of the image counts with Z, and this allows us to directly interpret image contrast at atomic columns positions as the number of atoms in projection. However, HAADF is only valid for atom counting of heavy elements that scatter strongly at high-angle. Phase imaging techniques are more appropriate for counting light elements because they ensure the collection of weak scattering signals at low angles. Phase methods recover the phase of the electron wavefunction scattered by both light and heavy elements; however, this phase is not directly quantifiable due to coherence [4]. Here, we present a novel approach to phase quantification, based on the combination of HAADF atom counting and electron ptychography. Electron ptychography is a 4D STEM phase technique whereby we recover the complex exit wavefunction from a set of 2D coherent electron diffraction patterns collected over a 2D image grid. Unlike other phase recovery techniques, electron ptychography has the unique advantage that it can be performed simultaneously with HAADF imaging. This allows for atom counting of heavy elements which can be used as means to rescale the ptychographic phase and count the light elements [5-6]. Herein, we apply this novel quantitative ptychographic approach to determine the local sub-stoichiometric composition of CeO_2-x nanoparticles. Fig. 1 (a) illustrates a schematic of the 4D STEM ptychographic method, where the Ce atom count in (b), obtained from the simultaneously recorded HAADF image, is used to calibrate the ptychographic phase in (c) to count O atoms.

[1] L. Jones et al., Nano Lett. 14 (2014) 6336.
[2] S. Van Aert et al., Phys. Rev. B 87 (2013) 064107.
[3] A. Rosenauer et al., Ultramic. 109 (2009) 1171.
[4] D. Van Dyck et al., Nature 486 (2012) 243.
[5] H. Yang et al., Nat. Comm. 7 (2016) 12532.
[6] A. De Backer et al., Ultramic. 171 (2016) 104.

Knowing the 3D atomic structures of materials or biomolecules is crucial for understanding their functions. X-ray diffraction is currently the most important technique for determination of 3D atomic structures, but requires large crystals which are often difficult to obtain. Electrons, similar to X-rays and neutrons, are powerful source for diffraction experiments. Due to the strong interactions between electrons and matter, crystals that are considered as powder in X-ray crystallography can be treated as single crystals by 3D electron diffraction methods [1]. This enables structure determination of materials and organic molecules from micron- to nanometer-sized 3D crystals that are too small for conventional X-ray diffraction. Furthermore, by taking the advantages of the unique properties of electron scattering, it is possible to determine the charge states of atoms/ions [2] and the absolute structure of chiral crystals [3].

Over the past decades, a number of 3D ED methods have been developed for structure determination. At the early stages of 3D ED method development, tilting of the crystal was done manually, while diffraction patterns were collected on negative film. It could take years before sufficient data were obtained and processed in order to determine the crystal structure. The computerization of TEMs and the development of CCD detectors allowed software to be developed that can semi-automatically collect 3D ED data in less than an hour [1]. Thanks to the recent advancement in CMOS and hybrid detector technology, it is now feasible to collect diffraction data in movie mode while continuously rotating the crystal (continuous rotation election diffraction, cRED, also known as MicroED [4] in structural biology). Benefiting from these technological advances, structure determination can now be accomplished within a few hours. Recently, fully automated serial rotation electron diffraction data collection and processing has been realized by our group [5].

By using 3D ED / MicroED methods, we have solved more than 200 novel crystal structures of small inorganic compounds [6] (including zeolite, MOF, COF and minerals) and biomolecules [7,8] (pharmaceuticals, small organic molecules, peptides and proteins) in the past 7 years. Recently, we have solved two novel protein [9,10] structures with 3D ED/MicroED and shown that it is feasible to use MicroED for structure based drug discovery [11]. We aim to further improve these methods, develop new methods and more importantly spread them to labs around the world.

[1] Gemmi M., Mugnaioli E., Gorelik T. E., Kolb U., Palatinus L., Boullay P., Hovmöller S. & Abrahams J. P. (2019). ACS Cent. Sci. 5, 1315–1329.

[2] Yonekura K., Kato K., Ogasawara M., Tomita M. & Toyoshima C. (2015). Proc. Natl. Acad. Sci. 112, 3368–3373.

[3] Brázda P., Palatinus L. & Babor M. (2019). Science. 364, 667–669.

[4] Shi D., Nannenga B. L., Iadanza M. G. & Gonen T. (2013). eLife. 2, e01345.

[5] Wang B., Zou X. & Smeets S. (2019). IUCrJ. 6, 854–867.

[6] Huang Z., Willhammar T. & Zou X. (2021). Chem. Sci. 12, 1206–1219.

[7] Clabbers M. T. B. & Xu H. (2020). Drug Discov. Today Technol., S1740674920300354.

[8] Clabbers M. T. B. & Xu H. (2021). Acta Crystallogr. Sect. Struct. Biol. 77, 313–324.

[9] Xu H., Lebrette H., Clabbers M. T. B., Zhao J., Griese J. J., Zou X. & Högbom M. (2019). Sci. Adv. 5, eaax4621.

[10] Clabbers M. T. B., Holmes S., Muusse T. W., Vajjhala P., Thygesen S. J., Malde A. K., Hunter D. J. B., Croll T. I., Flueckiger L., Nanson J. D., Rahaman H., Aquila A., Hunter M. S., Liang M., Yoon C. H., Zhao J., Zatsepin N. A., Abbey B., Sierecki E., Gambin Y., Stacey K. J., Darmanin C., Kobe B., Xu H. & Ve T. Nat. Commun. (In Press)

[11] Clabbers M. T. B., Fisher S. Z., Coinçon M., Zou X. & Xu H. (2020). Commun. Biol. 3, 417.

The project is supported by the Knut and Alice Wallenberg Foundation (2018.0237, X.Z.), the Swedish Research Council (2017-05333, H.X.; 2019-00815, X.Z.) and the Science for Life Laboratory through the pilot project grant Electron Nanocrystallography, and MicroED@SciLifeLab.

Quantitative convergent-beam electron diffraction (QCBED) has become renowned for its accuracy and precision when it comes to measuring bonding electrostatic potentials and electron densities [1 – 3]. Density functional theory (DFT) needs no introduction because of its ubiquity in materials science and crystallography. It is efficient but compromised in accuracy by the approximations needed to make it less computationally expensive than many-body wave-function calculations. It is also feared by some that DFT is becoming over-parametrised in the bid to deal with the shortcomings of approximations and is therefore “straying from the path toward the exact functional” [4].

We have integrated DFT into QCBED in such a way that allows DFT model parameters, including parameters associated with density functionals, to be refined by fitting DFT-calculated convergent-beam electron diffraction (CBED) patterns to experimental CBED patterns from a real material. We call this QCBED-DFT [5] and illustrate the basic principle of the method in Fig. 1 below.

We will present a number of experimental measurements of density functional parameters such as the Hubbard energy, U, in some strongly correlated electron materials, NiO and CeB₆, from our recently published work [5], as well as some new, unpublished trials.

[1] Zuo, J. -M., Kim, M., O’Keeffe, M. & Spence, J. C. H. (1999). Nature 401, 49.

[2] Nakashima, P. N. H., Smith, A. E., Etheridge, J. & Muddle, B. C. (2011). Science 331, 1583.

[3] A. Genoni, L. Bučinský, N. Claiser, J. Contreras‐García, B. Dittrich, P.M. Dominiak, E. Espinosa, C. Gatti, P. Giannozzi, J. Gillet, D. Jayatilaka, P. Macchi, A.Ø. Madsen, L. Massa, C.F. Matta, K.M. Merz Jr, P.N.H. Nakashima, H. Ott, U. Ryde, K. Schwarz, M. Sierka, S. Grabowsky (2018). Chem. Eur. J. 24, 10881.

[4] Medvedev, M. G., Bushmarinov, I. S., Sun, J., Perdew, J. P. & Lyssenko, K. A. (2017). Science 355, 49.

[5] Peng, D. & Nakashima, P. N. H. (2021). Phys. Rev. Lett. 126, in press.

We thank the late Prof. Andrew Johnson. We are grateful to the Monash Centre for Electron Microscopy where the CBED data were collected. Many thanks to Prof. Joanne Etheridge for her valuable advice throughout this work. PN thanks the Australian Research Council for funding (FT110100427 & DP210100308).

3D electron diffraction (3D ED) undergoes rapid development in the past years. Structure solution is relatively easy, dynamical refinement provides accurate structure models and also absolute structure determination [1], but the accuracy of the lattice parameters remains a problem despite some effort. Lattice parameters obtained by 3D ED have at least an order of magnitude lower accuracy than single crystal x-ray data and the comparison is even worse with powder x-ray data. The reasons causing this poor accuracy are instrument-induced geometrical distortions present in the data and, in case of beam sensitive samples, crystal damage induced by the electron beam. In 2D diffraction patterns, distortions caused by aberrations of electromagnetic lenses are well known and have been analysed several times [2], but the precession assisted data collection induces new distortion, which were never analysed and we quantify and describe them for the first time. For mathematical description, we split the total in-plane difference between the expected and observed position of the diffraction maxima into radial and tangential (Dr and Dt) contributions, which are then described by circular harmonics - function of diffraction vector length r and azimuth j of the diffraction maximum (eq. 1).

Parameters j_r,n, j_t,n, r_n,m and t_n,m need to be determined either by the calibration of the microscope or by the refinement against the diffraction data. This general approach allowed us to compensate for all observed distortions, not only the classical pincushion-barrel, spiral and elliptical. The distortions depend on excitation of the lenses and can be calibrated. Tools for distortion refinement are incorporated in software PETS 2 [3] and distortion refinement workflow may be found in Jana Cookbook example Borane [4].

The effects of geometrical distortions in 3D ED data was so far only marginally analysed [3]. Here we analyse the effects of both the distortions in the plane of diffraction image and also the errors in the crystal orientation. The effect of the accumulated electron dose is also significant (Figure 1). Measurements of anti-B₁₈H₂₂ molecular crystal shows that the beam damage results in lattice parameters increase by about 1.5(5)‰ per accumulated dose of 1 e^-.Å^-2.

Recent developments in the ability to control the shape of metal nanocrystals using wet chemistry synthesis techniques have drawn significant attention for potential applications in plasmonics, photonics and catalysis. It is conjectured that shape control can be achieved by controlling the nanocrystal surface structure, primarily using surfactants and metal additives. For example, various shapes of Au nanoparticles, including rods, cubes, decahedra and octahedra, can be grown selectively using a trace amount of Ag [1] or Cu [2] additives. Understanding the underlying mechanisms of shape control by metal additives is therefore vital for the further engineering of nanocrystals. However, the establishment of atomic structure models of metal additives on the nanocrystal surface, that are just a few atoms wide, is still challenging.

For this aim, there are three essential requirements of the characterisation technique: (1) sufficient chemical sensitivity to distinguish surface additives; (2) spatial resolution at the atomic scale; (3) avoidance of damage to the surface structure from the probe.

Scanning transmission electron microscopy (STEM) has been widely used as a powerful means of resolving atomistic structures of nanocrystals. In this study, we studied the structure of Cu additives on the surface of Au nanocubes using conventional energy dispersive X-ray spectroscopy STEM (EDX-STEM) and high-angle annular dark filed STEM (HAADF-STEM), as well as four-dimensional STEM (4D-STEM) tuned specifically for the detection of surface adatoms.

EDX-STEM mapping reveals the presence of Cu on the {100} surfaces of Au nanocubes. However, the high electron dose required to achieve meaningful statistics can damage the structure during acquisition so a quantitative, high resolution analysis of an undamaged surface is not possible.

HAADF-STEM collects electrons at high angles by an annular detector and presents intensity sensitive to the atomic number (Z), however, it is also sensitive to other material parameters such as thickness and local environments (such as vacuum) [3,4]. We observe the intensity to drop at the nanoparticle atomic surface layer in the HAADF-STEM image but cannot distinguish whether this is due exclusively to the presence of (lower Z) Cu atoms or just fewer atoms on the surface layer. Furthermore, this is a dose-inefficient technique, using only those electrons scattered to high angles, and surface modification can be observed during acquisition.

4D-STEM using a fast pixelated detector records the full diffraction patterns at each probe position during the STEM experiment. The collected 4D datasets enable us to investigate features in diffraction patterns that are specifically related to different material parameters [4]. This method has the advantages of a lower dose than EDX-STEM and access to much more specimen information than HAADF-STEM. In this work, we developed an iterative method by starting with an ideal nanocube model with uniform thickness and with/without surface Cu layers. Dynamic diffraction conditions and scattering angles sensitive to the presence of Cu additives were identified based on the comprehensive dynamical scattering 4D-STEM simulations of this initial model. We then collected experimental 4D-STEM datasets using our optimised imaging conditions, from which Cu adatoms on the surface were evident with excellent contrast. In the next step, a matching of experimental diffraction patterns with simulated diffraction patterns was conducted to determine the realistic surface thickness profile. These allowed us to further refine the nanocube model using the observed surface structure of Cu adatoms and fitted thickness profile for the ultimate 4D-STEM simulations. Excellent agreement was achieved in both qualitative and quantitative comparisons between 4D-STEM simulations and 4D-STEM experiments over various imaging models (which each correspond to different diffraction physics). This suggests that the refined nanocube surface model represents the actual structure of Cu additives on the surface of Au nanocubes. This provides an approach for identifying the type and arrangement of the critical surface atoms that play an important role in controlling the growth and shape of nanoparticles.

[1] Personick, Michelle L., et al. Nano letters 11.8 (2011): 3394-3398. [2] Sun, Jianhua, et al. Crystal Growth and Design 8.3 (2008): 906-910.[3] LeBeau, James M., et al. 100.20 (2008): 206101. [4] Cowley, John. M. Surface Science 114.2-3 (1982): 587-606.[4] Ophus, Colin. Microscopy and Microanalysis 25.3 (2019): 563-582.

Keywords: Metal nanocrystals; Metal additives; Surface structure; 4D-STEM; STEM simulation

This work was carried out on the microscopes at the Monash Centre for Electron Microscopy funded by ARC grant number (LE0454166). This work was supported by ARC funding Discovery Project number DP160104679.

One of major crystallographic challenges is how to determine the structure of severely distorted crystal lattices, such as at a dislocation core and in high entropy alloys where distortion is non-uniform. Here we propose a new 4D scanning transmission electron microscopy (4D-STEM) based technique, called Cepstral STEM, for imaging disordered crystals using electron diffuse scattering. Local fluctuations of diffuse scattering are captured by scanning electron nanodiffraction (SEND) using a coherent probe. The harmonic signals in electron diffuse scattering are detected through Cepstral analysis and used for imaging. By integrating Cepstral analysis with 4D-STEM, we demonstrate that information about the distortive part of electron scattering potential can be separated and imaged at nm spatial resolution. We apply our technique to the analysis of a dislocation core in SiGe and lattice distortions in high entropy alloy [1].

[1] Yu-Tsun Shao, Renliang Yuan, Haw-Wen Hsiao, Qun Yang, Yang Hu, and Jian-Min Zuo, "Cepstral scanning transmission electron microscopy imaging of severe lattice distortions", Ultramicroscopy, 113252 (2021).

Three-dimensional electron diffraction 3DED has turned nowadays into a reliable and promising method used worldwide for the crystal structure analysis of nanoparticles [1]. Since the first attempts to fine scan the electron diffraction space and use the reconstructed reciprocal volume for single crystal structure analysis [2] the method has been adapted in great variety in several labs. In comparison to traditionally applied 3DED methods, where series of oriented diffraction patterns are collected and indexed individually, automated diffraction tomography (ADT) provides major improvements of diffraction data. Scanning the diffraction space while tilting the crystal delivers non-oriented diffraction patterns with reduced dynamical scattering effects, allows to collect the full diffraction information throughout the acquisition range thus providing an enhanced coverage of the expected diffraction intensities as well as improved diffraction intensity determination. The subsequent three dimensional reconstruction of electron diffraction data provides all information necessary for single crystal structure solution [3]. Dedicated data acquisition strategies and data processing routines allow the investigation of highly beam sensitive material as well as complicated crystallographic features such as the detection and quantitative description of diffuse scattering effects, twinning, superstructures or modulations.

Crystal structures solved “ab initio” with ADT run through a large number of scientific areas and range from the first structural analysis of barite [3] to complex minerals [4], from the first small organic molecule [5] to large organometallic networks [6], from ZSM-5 single crystals [7] to stacked zeolites and layered silicates [8], from the first pseudo symmetric chalcogenide [9] to complicated oxides covering twinned and modulated materials. Many hitherto unknown crystal structures could be solved by 3DED, several of them new and unexpected structures of often metastable compounds [10].

[1] Gemmi, M., Mugnaioli, E., Gorelik, T.E. Kolb, U., Palatinus, L., Boullay, Ph., Hovmöller, S. Abrahams, J.-P. (2019). ACS Cent. Sci. 5, 1315.

[2] Kolb, U., Gorelik, T., Otten, M. (2008). Ultramic. 108, 763.

[3] Mugnaioli, E., Gorelik, T., Kolb, U. (2009) Ultramic. 109, 758.

[4] Rozhdestvenskaya, I., Mugnaioli, E., Czank, M., Depmeier, W., Kolb, U., Reinholdt, A., Weirich, T. (2010) Mineralogical Magazin,74(1), 159.

[5] Kolb, U., Gorelik, T., Mugnaioli, E., Stewart, A. (2010) Polymer Reviews, 50, 385.

[6] Rhauderwiek, T., Zhao, H., Hirschle, P., Doblinger, M., Bueken, B., Reinsch, H., De Vos, D., Wuttke, S., Kolb, U., Stock, N. (2018) Chem. Sci. 9, 5467.

[7] Mugnaioli, E., Kolb, U. (2014) Microporous and Mesoporous Materials, 189, 107. [8] Krysiak, Y., Maslyk, M., Silva, B.N., Plana-Ruiz, S., Moura, H.M., Munsignatti, E.O., Vaiss, V.S., Kolb, U., Tremel, W., Palatinus, L., Leitão, A.A., Marler, B,, Pastore H. O. (2021), Chem. Mater. 33, 3207.

[9] Birkel, C., Mugnaioli, E., Gorelik, T., Panthöfer, M., Kolb, U., Tremel, W. (2010) J.A.C.S. 132(28) 9881.

[10] Zou, Z., Habraken, W.J.E.M., Matveeva, G., Jensen, A.C.S., Bertinetti, L., Hood, M.A., Sun, Ch-Y. Gilbert, P.U.P.A, Polishchuk, I., Pokroy, B., Mahamid, J., Politi, Y., Weiner, S., Werner, P., Bette, S., Dinnebier, R., Kolb, U. Zolotoyabko, E., Fratzl, P. (2019), Science, 363, 396.

Modern electron crystallography started off in the 1960-ies by the work of Aaron Klug and collaborators in Cambridge, UK. At that time the resolution was around 25 Ångström - enough for showing the icosahedral envelopes of spherical viruses. In 1975 Nigel Unwin and Richard Henderson solved the first structure of a membrane protein, bacteriorhodopsin, using Fourier analysis of EM images of 2D crystals of the protein. The resolution was 7 Å.

In parallel, but essentially without contact with the molecular biologists, inorganic structures were also studied by electron microscopy. The resolution of 3.5-4 Å in the 1970-ies was just enough to see metal atoms in oxides. In 1984 we determined the atomic positions of metal atoms in an Nb/W-oxide by EM to an accuracy of about 0.1 Å.

Because of a confused nomenclature regarding the word "phase", the two communities biological and physical, hardly spoke to each other for decades. Crystallographers consider "phase" as crystal structure factor phases, which describe standing waves of electron density in crystals. These waves have wavelengths that correspond to the d-spacings of reflections. In contrast, the physicists studying inorganic compounds by EM, talked about the phases of the electron waves propagating through the crystals. The wavelengths of these waves are determined by the acceleration voltage of the electron microscope used. For 100 kV to 300 kV, these wavelengths are about 0.037 to 0.025 Å. Already by comparing the wavelengths, it is obvious that the two types of phases are different.

Furthermore, the “structure factor phases” are relative to the fixed position of an origin in the unit cell; a position specific for each of the 230 space groups and listed in the International Tables for Crystallography. The “electron wave phases” are relative to the electron wave as it propagates through the crystal at about half the speed of light. Most importantly, the “structure factor phases” are present in the EM images, as Aaron Klug had already explained in the 1960-ies. These phases can be read out from the Fourier transform of an EM image. In contrast, the “electron wave phases” are lost in the EM images. The phases are always lost in diffraction patterns, whether X-ray or electron diffraction.

The confusion as to the presence or not of the phases in EM images was so large that I wasn’t invited as a speaker at the first Electron Crystallography Schools organized by IUCr in Beijing 1993 and Bristol 1994, because “Hovmöller confuses the students”. As a reaction to this, Xiaodong Zou and I started our own schools of electron crystallography in Stockholm. From a very modest scale with just a dozen participants, these schools grew and became annual. The greatest honour was when we were invited by Lodovico Riva de Sanseverino to arrange one of the IUCr schools in Erice. This has since become a tradition every seven years.

X-ray crystallography has been done in 3D right from the start, when the structure of NaCl was solved by Bragg & Bragg in 1912. But electron crystallography for minerals and other inorganic crystals remained in 2D, limiting the structures that could be investigated. In the 1980-ies, we developed the software program CRISP, based on the methods developed in Cambridge for Fourier analysis of EM images. At that time, the great concern about distorted intensities in electron diffraction patterns due to multiple scattering, hampered the development.

A major breakthrough was the invention of the precession electron diffraction technique by Roger Vincent and Paul Midgley in Bristol 1994. It was obvious already by just looking at the electron diffraction patterns that the intensities now were much closer to kinematical. However, it was still only in 2D. The step into 3D came as a result of improved instrumentation combined with software developments. The electron microscopes could be programmed to take series of hundreds of diffraction patterns in just minutes. The diffraction patterns were recorded on very fast detectors (cameras). Systems with different geometries, but fundamentally similar, were then developed independently by Ute Kolb and her group in Mainz (ADT) and by our group in Stockholm (RED). Data collection that previously required days or weeks, was speeded up first to hours and now to minutes or even seconds.

With the new techniques RED (rotation electron diffraction) and ADT (automatic diffraction tomography), the data quality was also substantially improved. The intensities obtained by electron diffraction are now approaching those by X-ray diffraction. Perhaps even more important than reliable intensities, is the fact that these modern ways of electron diffraction give us (nearly) complete 3D data.

Today, 3D electron diffraction has become a fast and highly reliable method for crystal structure determination. Data is collected as fast as with synchrotrons. Because of the very strong interaction of electrons with matter, even the finest powder diffracts like single crystals. Hundreds of structures have now been solved by electron diffraction. From zeolites and metal-organic frameworks (MOF) to quasicrystal approximants, pharmaceutics and proteins are solved from sub-micrometer sized crystals, too small even for synchrotrons.

Finally, after half a century of efforts, electron crystallography is no longer a peculiar young brother from the countryside (compared to X-ray crystallography) but a mature science in its own right.

Flexible materials can adapt their structures easily in response to external stimuli. For this reason, they are often used as sensors or actuators; they can show useful and unusual mechanical behaviour such as negative thermal expansion or negative compressibility. In a conceptually related manner, disordered materials navigate a shallow configurational landscape of degenerate states. This degeneracy also often heightens their susceptibility to external perturbations. This lecture will explore the fundamental design principles associated with structural flexibility and correlated disorder, and their role in a range of functional materials. Case studies taken from our own work will includie metal–organic frameworks, oxide ceramics, and frustrated magnets.

X-ray diffraction from powders and single crystals has for decades been the key analytical tool in materials science. Bragg intensities provide information about the average crystals structure, but often it is disorder and specific local structure that control key material properties. For 1D data there has been an immense growth in combined analysis of Bragg and diffuse scattering using the Pair Distribution Function (PDF), and in our group we frequently use 1D PDF analysis to study nanocrystal nucleation in solvothermal processes [1] or thin films [2], or to analyse materials under operating conditions [3]. For single crystals, diffuse scattering studies have a long history with elaborate analysis in reciprocal space, but direct space analysis of the 3D-PDF is still in its infancy. We have used 3D-PDF analysis to study the crystal structures of high performance thermoelectric materials Cu₂Se (Fig 1) [4], PbTe [5], and 19-e half-heusler Nb_1-xCoSb [6], where the true local structure is essential for understanding the unique properties. For frustrated magnetic materials direct space analysis of diffuse magnetic scattering provides a new route to magnetic structures [7].

[1] N. L. N. Broge et al., Auto-catalytic formation of high entropy alloy nanoparticles, Angew. Chem. Intl. Ed., 59, 21920-21924 (2020)

[2] M. Roelsgaard et al., Time-Resolved Surface Pair Distribution Functions during Deposition by RF Magnetron Sputtering, IUCrJ, 6, 299–304 (2019)

[3] L. R. Jørgensen et al., Operando X-ray scattering study of thermoelectric β-Zn₄Sb₃, IUCr-J, 7, 100-104 (2020)

[4] N. Roth et al., Solving the disordered structure of β-Cu_2-xSe using the three-dimensional difference pair distribution function, Acta Crystallogr. Sect. A, 75, 465–473 (2019)

[5] K. A. U. Holm et al., Temperature Dependence of Dynamic Dipole Formation in PbTe, Phys. Rev. B, 102, 024112 (2020)

[6] N. Roth et al., A simple model for vacancy order and disorder in defective half-Heusler systems, IUCrJ, 7, 673-680 (2020)

[7] N. Roth et al., Model-free reconstruction of magnetic correlations in frustrated magnets, IUCr-J, 5, 410–416 (2018)

Many advanced functional properties of crystalline materials derive from complex disorder and short-range correlations that emerge from a subtle balance among competing interactions involving spin, charge, orbital, and strain degrees of freedom. Materials that harbor such disorder generally exhibit strongly enhanced responses, with electronic, magnetic, optical, and thermal properties that are extremely sensitive to perturbations such as magnetic or electric fields and are of considerable importance for future applications. Obtaining a detailed understanding of such complex disorder is required to control and exploit these unusual patterns that persist within short-range ordered states in order to access functional responses inaccessible to conventional, long-range ordered materials. Diffuse scattering is a powerful probe of such complex disorder and when measured from single crystals over large 3D volumes of reciprocal space provides detailed information regarding the existence and morphology of local distortions, as well as defect–defect correlations, i.e., the tendency for defects to cluster into nanoscale ordered structures [1,2].

Recent developments in instrumental advances now efficient measurements of single crystal diffraction data over large volumes of reciprocal space using synchrotron x-rays or neutrons. For the latter, dedicated instrumentation, in particular the Corelli instrument at the Spallation Neutron Source, has been constructed that enables measurements of such volumes with elastic discrimination [3]. The value of combining the complementarity of neutrons and x-rays of such measurements over large space of temperature and compositions will be demonstrated on recent investigation of relaxor ferroelectrics that provide new insight on the relation of local order to material properties relaxors [4]. While analyzing diffuse scattering data and obtaining detailed models of the underlying remains challenging, the availability of comprehensive measurements of the scattering over large 3D volumes enables new ways of analyzing the data, by utilizing the 3D-ΔPDF method [5]. This method allows to derive for example, direct, model free reconstructions of ionic correlations [6], which are essential in many energy materials, as well as magnetic correlations in frustrated magnets [7]. Recent advances in Machine Learning methods further provide invaluable and new, rapid insight into the information contained in these large data sets, in particular when measured over varying experimental parameters such as temperature or external fields [8].

[1] Welberry,T.R. Weber, T. (2016) Crystallography Reviews 22, 2-78[2] see contributions in Issue Diffuse Scattering (2005). Z. Kristallogr. Cryst. Mater. 220, Issue 12[3] Ye, F., et al. (2018). J. Appl. Cryst.. 51, 315 - 322.[4] Krogstad, M.J., et al. (2018). Nat. Mater. 17, 718 - 724.[5] Weber, T., Simonov, A. (2012). Z. Kristallogr. 225, 238.[6] Krogstad, M.J, et al. (2020). Nat. Mater. 19, 63 - 68.[7] Roth, N., May, A.F., Ye, F., Chakoumakos, B.C., Iversen, B.B. (2018). IUrJ. 5, 410.[8] Venderley, J., et al. (2020). Cond-Mat. Archiv arXiv:2008.03275.

Keywords: IUCr2020; abstracts; total scattering; single crystal diffuse scattering, complex disorder, short range correlations

Work supported by U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division

Many important functional materials are complex mixtures that derive their properties from the interplay of various individual component phases. In each case, the interfaces between phases are a crucial component in their own right, since they are the point at which much of the key chemistry (and/or physics) takes place [1, 2]. By their very nature, interfaces are notoriously more difficult to characterise than the bulk phases they connect; and the process of translating experimental measurements into a picture of atomic-scale structure remains a significant general challenge [3]. Here we explore the possibility that pair distribution function (PDF) measurements offer sensitivity to interface structure in a way that is strongly complementary to existing experimental and computational approaches.

Using a non-negative matrix factorisation (NMF) approach [4, 5], we show how the PDF of complex mixtures can be deconvolved into the contributions from the individual phase components and also the interface between phases. Our focus is on the model system Fe||Fe₃O₄. First, we establish proof-of-concept using idealised PDF data generated from established theory-driven models of the Fe|| Fe₃O₄ interface. Using X-ray PDF measurements for corroded Fe samples, and employing our newly-developed NMF analysis, we extract the experimental interface PDF (‘iPDF’) for this same system. We find excellent agreement between theory and experiment.

[1] Baraff, G. A., Appelbaum J. A. & Hamann, D. R. (1977) Phys. Rev. Lett. 38, 237.

[2] Harrison, W. A., Kraut, E. A., Waldrop J. R. & Grant R. W. (1978) Phys. Rev. B 18, 4402.

[3] Goodwin, A. L. (2019) Nat. Commun. 10, 4461.

[4] Lee, D. D. & Seung, H. S. (1999) Nature 401, 788.

[5] Geddes, H. S., Blade, H., McCabe, J. F., Hughes, L. P. & Goodwin, A. L. (2019) Chem. Commun. 55, 13317.

Complementary to x-ray diffraction patterns that represent the crystal lattice in Q space, the atomic pair distribution function (PDF) describes the structure of a material as a histogram of interatomic distances r in real space. The total scattering (TS) approach that enables PDF analysis requires that scattering data is collected over a wide Q range of the order of 20 Å^-1 and subsequent Fourier transformation of the entire scattering pattern into direct space. While TS at high-energy beamlines has become a standard routine for bulk-type samples, the unfavorable thickness ratio of a thin film (nanometer regime) to its substrate (micrometer regime) limits the detectability of the film signal in simple transmission geometry as described e.g. in Ref. [1]. Therefore, we applied the high-energy surface diffraction technique established for single-crystal surfaces [2] to less ordered films and thus pushed the capabilities for PDF analysis of thin films to unprecedented limits in terms of minimum thickness and time resolution. [3,4] Besides polycrystalline and textured metal and oxide layers, we studied amorphous and naocrystalline thin films. By careful data treatment, we successfully derived PDFs of comparable data quality from different HfO₂ films with thicknesses down to 15 nm independent on their degree of ordering with domain sizes between ~5 and >30 Å. All films were deposited on fused silica which provides an easily scalable background to subtract from the sample data to isolate the film signal. Real thin film devices e.g. for electronic applications, however, typically consist of multiple layers, and the film growth is largely affected by the nature of the underlying layer. Therefore, we further developed grazing incidence total scattering towards a depth-resolving method by scanning the incidence angle. In this way, the technique provided insight into the structure of different types of bilayer samples studied for their use e.g. in next-generation computer memory applications. PDFs were successfully extracted from the individual layers of different combinations and stackings of amorphous and crystalline materials exhibiting high and low (electron) density and, hence, x-ray scattering power from TiO₂ to Pt [5]. As thermal treatment is an essential part of thin film device manufacturing, we are developing a laser-interferometer based system that, beyond data collection during isothermal heat-treatment as applied in [4], enables following structural changes during variable-temperature processes up to several hundred degrees. Fig. 1 shows data from the proof-of-concept experiment on a 30 nm HfO₂ thin film deposited by chemical vapor deposition in an amorphous state, crystallized in situ while continuously acquiring TS data.

The antiferromagnetic semiconductor MnTe has recently attracted significant attention as both a high-performance thermoelectric and a candidate material for spintronics. The magnetic properties of MnTe play a crucial role in both of these technological applications. MnTe has a hexagonal layered structure in which magnetic Mn2+ spins order ferromagnetically within the plane and antiferromagnetically between the planes below TN = 307 K. Above TN, robust short-range magnetic correlations survive to high temperature. It has been shown that these short-range correlations are a significant contributor to the high thermoelectric figure of merit zT in MnTe through a mechanism known as paramagnon drag. Here, we present comprehensive atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering data collected from pure and doped MnTe powders, together with three-dimensional magnetic PDF data obtained from a single crystal of MnTe. These complementary data sets allow us to track in detail the evolution of the magnetic correlations from the long-range ordered state at low temperature to the short-range ordered state at high temperature. We present real-space magnetic models that reproduce the observed mPDF patterns with quantitative accuracy and discuss the significance of these results in the context of existing work on MnTe.

The local structure of NaTiSi₂O₆ is examined across its Ti-dimerization orbital-assisted Peierls transition at 210 K. An atomic pair distribution function approach evidences local symmetry breaking pre-existing far above the transition. The analysis shows the dimers evolve on heating into a short-range orbital degeneracy lifted (ODL)[1] state of dual orbital character, present up to at least 490 K. The ODL state is correlated over the length scale spanning ~6 sites of the Ti zigzag chains. Our results imply that the ODL phenomenology extends to strongly correlated electron systems.

My laboratory studies the structures of membrane proteins that are important in maintaining homeostasis in the brain. Understanding structure (and hence function) requires scientists to build an atomic resolution map of every atom in the protein of interest, that is, an atomic structural model of the protein of interest captured in various functional states. In 2013 we unveiled the method Microcrystal Electron Diffraction (MicroED) and demonstrated that it is feasible to determine high-resolution protein structures by electron crystallography of three-dimensional crystals in an electron cryo-microscope (CryoEM). The CryoEM is used in diffraction mode for structural analysis of proteins of interest using vanishingly small crystals. The crystals are often a billion times smaller in volume than what is normally used for other structural biology methods like x-ray crystallography. In this seminar I will describe the basics of this method, from concept to data collection, analysis and structure determination, and illustrate how samples that were previously unattainable can now be studied by MicroED. I will conclude by highlighting how this new method is helping us discover and design new drugs; shedding new light on chemical synthesis and small molecule chemistry; and showing us unprecedented level of details with important membrane proteins such as ion channels and G-protein coupled receptors (GPCRs).

X-ray powder diffraction and electron single crystal diffraction, although having very different methodologies in their cores, target the same material, and can deliver complimentary information for the structure characterization.

X-ray powder diffraction is a well-established technique; its performance can be exemplified by a number of impressive highlights [1-3]. A structure analysis with powder X-ray diffraction runs thorough three main steps – (i) indexing of the powder profile, (ii) structure solution, and (ii) structure refinement. The first step represents the bottleneck for the whole procedure, being associated with the inherent problem of the powder method – projection of all reflections onto a single axis. The most difficult cases represent polyphasic samples, large unit cell volumes, and low symmetry structures.

Electron diffraction method, being able to address nanocrystals individually, allows to collect 3D single crystal data from crystals with the size down to tens of nanometres [4]. A 3D reconstruction of the reciprocal space immediately delivers information on the unit cell metric. The inherent problems of electron diffraction appear at later stages, when quantification of reflection intensities is required. The strong interaction of electrons with matter gives rise to multiple scattering, which modifies intensities of reflections in a complex manner. Recently, methods for dynamical structure refinement became available [5]; still the multiple scattering contribution cannot be accounted for during the structure solution (model building) step.

In this light, an obvious beneficial combination of two techniques is the transfer of unit cell parameters, determined from electron diffraction to powder X-ray data for subsequent structure solution and refinement. This workflow will be demonstrated by examples. Beyond this combination, analysis of diffuse scattering by the two methods will be presented, and combined analysis of total scattering for PDF calculation will be discussed.

[1] Vella-Zarb, L., Baisch, U., Dinnebier, R. E. (2013). J. Pharm. Sci., 102, 674. [2] Schlesinger, C., Bolte, M. and Schmidt, M. U. (2019). Z. Kristallogr. 234, 257. [3] Spiliopoulou, M. Karavassili, F. Triandafillidis, D.-P. Valmas, A. Fili, S. Kosinas, C. Barlos, K. Barlos, K. K. Morin, M. Reinle-Schmitt, M. L. Gozzo F. and Margiolaki, I. (2021). Acta Cryst. A77. [4] Gemmi, M., Mugnaioli, E., Gorelik, T.E., Kolb, U., Palatinus, L., Boullay, P., Hovmöller, S., Abrahams, J.P. (2019). ACS Cent. Sci. 5, 1315. [5] Palatinus, L. Brázda, P. Jelínek, M. Hrdá J., Steciuk, G. Klementová M. (2019). Acta Cryst., B75, 512.

Unit cell determination, phase identification, structure determination, structure refinement. At one point of time, X-ray powder diffraction (XRPD) was the way to go for structure characterization of microcrystalline powders, despite the analyses sometimes being slow and tedious. For a long time, we have known that electron diffraction (ED) data from microcrystals are useful for unit cell and structure determination. We would still resolve to XRPD for structure refinement, because the data are kinematical and therefore simpler to model.
Over the last 15 years, developments in ED methodology, both hardware and software, have reached a point where high-quality data can be collected routinely on a large number of crystals [1, 2]. When of sufficient quality, structures refined against these data challenge the accuracy of what can be obtained from XRPD data. By combining data from different crystals using cluster analyses, we showed that even physically meaningful anisotropic ADPs can be obtained from ED data [3]. These are notoriously difficult to obtain from XRPD data.
What can we not do with ED? Through serial crystallography experiments, we saw that it is possible to collect ED data from hundreds or thousands of crystals automatically [2]. This opens the door for automated quantitative phase analysis using ED data [3, 4, 5], challenging the bulk information that can be obtained from XRPD data. Then what do we still need XRPD data for?

[1] M.O. Cichocka, J. Ångström, B. Wang, X. Zou, S. Smeets, J. Appl. Cryst. 51(6), 1652-1661
[2] B. Wang, X. Zou, S. Smeets, IUCrJ 6(5), 854-867
[3] S. Smeets, S. I. Zones, D. Xie, L. Palatinus, J. C. Pascual, S.-J. Hwang, J. E. Schmidt, L. B. McCusker, Angew. Chem. Int. Ed. 58(37), 13080-13086
[4] S. Smeets, J. Ångström, C. O. A. Olsson, Steel Res. Int. 90(1), 1800300
[5] Y. Luo, B. Wang, S. Smeets, J. Sun, W. Yang, and X. Zou, Manuscript in preparation.

Magadiite, Na₂Si₁₄O₂₈(OH)₂·nH₂O, is known as a mineral discovered at the lake Magadi in Kenya by Hans Eugster in 1967 [1]. Since then, magadiite-type materials have also frequently been synthesized in the lab and have come into focus for various applications [2-4], like CO₂ adsorbents, drug carriers or catalysts and maintain a rising interest.

Despite many attempts, the unique magadiite structure remained unsolved. Finally, a material-specific strategy based on 3D electron diffraction successfully deciphered the atomic structure [5]. In order to enable the ab initio structure solution of the electron beam sensitive material, a sodium-free dehydrated form of magadiite was synthetically isolated and, from that, it was subsequently possible to derive a structure model for the sodium form of magadiite, later successfully refined against powder X-ray diffraction data. Furthermore, a geometry optimization, simulations of spectroscopic data and calculation of charge transfer between the water molecules and the silicate layer with DFT methods confirmed the obtained crystal structure of sodium magadiite.

The structure of the silicate layer is quite complex, as it contains 4-, 5-, 6-, 7-, and 8-rings of three- and four-interconnected [SiO_4/2] tetrahedra. Seven symmetrically independent Si atoms and 15 independent oxygen sites are present forming a dense layer of considerable thickness (11.5 Å). The symmetry can be described by the layer group c211. Each layer is chiral, but the chirality of the stacked silicate layers in the average structure (F2dd) is alternated, due to the glide plane perpendicular to the stacking axis. Bands of interconnected [Na(H₂O)_6/1.5]⁺ octahedra are intercalated between neighbouring silicate layers to compensate the charge of the layers.

The detailed knowledge now achieved on the previously unknown silicate layer and the development of an adapted synthesis combined with an ammonia-based titration will have a huge impact on the research of hybrid organic−inorganic nanocomposites based on magadiite, related layered silicates and zeolite-like structures in order to design new and more efficient materials.

Figure 1. Number of publications mentioning magadiite. Inset illustrates the structure of sodium magadiite with view along [110].

[1] Eugster, H. P. (1967). Science. 157, 1177–1180.

[2] Ge, M., Tang, W., Du, M., Liang, G., Hu, G. & Jahangir Alam, S. M. (2019). European Journal of Pharmaceutical Sciences. 130, 44–53.

[3] Paz, G. L., Munsignatti, E. C. O. & Pastore, H. O. (2016). Journal of Molecular Catalysis A: Chemical. 422, 43–50.

[4] Vieira, R. B., Moura, P. A. S., Vilarrasa-García, E., Azevedo, D. C. S. & Pastore, H. O. (2018). Journal of CO₂ Utilization. 23, 29–41.

[5] Krysiak, Y., Maslyk, M., Silva, B. N. N., Plana-Ruiz, S., Moura, H. M., Munsignatti, E. O., Vaiss, V. S., Kolb, U., Tremel, W., Palatinus, L., Leitão, A. A., Marler, B. & Pastore, H. O. (2021). Chemistry of Materials [accepted].

This research was supported by the Czech Science Foundation (project number 19-08032S).

Polymorphism is a common aspect of most commercially relevant drugs. One-third of crystalline organic molecules and about half of marketed active pharmaceutical ingredients (APIs) are known to form polymorphs [1, 2]. The characterization of all polymorphic species and the understanding of the overall polymorphic energy landscape represents a prominent aspect of drug development and is crucial to establish efficacy, formulation and shelf life. Moreover, the discovery of new polymorphs with different chemical and physical properties may result in treatments that are more effective and with reduced side effects [3].

Here, we report the crystallization, structure determination and dissolution behaviour of the δ-polymorph of the non-steroidal anti-inflammatory drug indomethacin (IMC), a poorly studied polymorph first mentioned almost 50 years ago [4] and whose structure has remained hitherto unknown. δ-IMC shows a significantly enhanced dissolution rate compared with the more common and thoroughly studied α- and γ-polymorphs, potentially connected with an increased bioavailability.

Pure δ-IMC was obtained via desolvation of the methanol solvate form. Its crystallisation results in fibrous crystals that are too tiny for conventional single-crystal X-ray diffraction (XRD). Structure determination was therefore obtained on the basis of continuous three-dimensional electron diffraction (3D ED) [5], recorded by a single-electron detector [6]. The structural model obtained from 3D ED was refined using the Rietveld method against powder XRD data, following the protocol used for other pharmaceutical compounds [7, 8] and allowing the accurate determination of free torsion angles and intermolecular bonding.

The structure solution provides a solid clarification of δ-IMC spectroscopic IR and Raman data and a tentative interpretation for still unsolved indomethacin metastable polymorphs. Moreover, it explains the observed solid-solid transition from the δ-polymorph to the α-polymorph, which is likely driven by similarities in molecular conformation.

The applied procedure for structure determination may be implemented as a standard protocol for the R&D department of a pharmaceutical company.

[1] Hilfiker, R. (2006). Polymorphism: In the Pharmaceutical Industry. Weinheim: Wiley.

[2] Cruz-Cabeza, A. J., Reutzel-Edens, S. M. & Bernstein, J. (2015). Chem. Soc. Rev. 44, 8619.

[3] Gao, L., Liu, G., Ma, J., Wang, X., Zhou, L. & Li, X. (2012). Controlled Release 160, 418.

[4] Borka, L. (1974). Acta Pharm. Suec. 11, 295.

[5] Gemmi, M., Mugnaioli, E., Gorelik, T. E., Kolb, U., Palatinus, L., Boullay, P., Hovmöller, S. & Abrahams, J. P. (2019). ACS Cent. Sci. 5, 1315.

[6] Nederlof, I., Van Genderen, E., Li, Y. W. & Abrahams, J. P. (2013). Acta Cryst. D69, 1223.

[7] Andrusenko, I., Hamilton, V., Mugnaioli, E., Lanza, A, Hall, C., Potticary, J., Hall, S. R. & Gemmi, M. (2019). Angew. Chem. Int. Ed. 131, 11035.

[8] Andrusenko, I., Potticary, J., Hall, S. R. & Gemmi, M. (2020). Acta Cryst. B76, 1036.

We thank Diamond Light Source Synchrotron Facility for obtaining simultaneous synchrotron powder XRD and differential scanning calorimetry (DSC) data.

The crystal structure of a novel high pressure, high temperature tin oxynitride phase (Sn₂N₂O) was solved via Automated Electron Diffraction Tomography (ADT) [1]. The new phase was synthesized from a Sn-N-O precursor at 20 GPa and 1200-1500°C. Due to strong overlaps of symmetrically non-equivalent reflections, attempts to solve the unknown structure based on X-ray powder diffraction data were not successful. The use of the ADT method allows to collect three dimensional electron diffraction data (3D ED) from single nanocrystals in the TEM via a tilt movement of the crystal and sequential diffraction pattern acquisition [2]. Subsequently, the reciprocal space is reconstructed and unit cell parameters as well as space group information can be derived. The electron diffraction intensities can be extracted and used to solve the crystal structure via approaches like “direct methods”.

The new oxynitride phase crystallizes in space group Pbcn with the unit cell parameters: a=7.83 Å, b=5.53 Å, c=5.54 Å. The crystal structure could be solved ab initio with direct methods and refined taking both the kinematic and dynamic theory of scattering into account. It resembles a Rh₂S₃ type structure where the Sn atoms are sixfold coordinated by O and N atoms. The refined structure compares very well with DFT calculations demonstrating the quality of data achievable with ADT and its applicability for the structure solution of high pressure and high temperature materials.

[1]Bhat S., Wiehl L., Haseen S., Kroll P., Glazyrin K., Gollé-Leidreiter P., Kolb U., Farla R., Tseng J., Ionescu E., Katsura T. & Riedel R. (2020). Chem. Eur. J. 26, 2187-2194

[2]Kolb U., Krysiak Y. & Plana-Ruiz S. (2019). Acta Cryst. B 75, (4) 463-474.

3D electron diffraction (3D ED) has recently emerged as an alternative to x-ray diffraction to elucidate the atomic structure of nano-sized beam sensitive crystals¹. LD-EDT² is a recently developed low dose 3D ED technique for ab initio structure determination of beam sensitive crystals such as hydrated minerals or MOFs. Low dose conditions are achieved by optimizing exposure during specimen tilting. High quality diffraction data can be obtained from very small crystals without damaging the structure, and a precise sampling of the reciprocal space is assured by beam precession. We recently applied LD-EDT on Bulachite³, a hydrated Al arsenate mineral, to solve its atomic structure. Difficulties related to the small size of crystals as well as beam sensitivity due to the presence of H2O molecules inside the lattice were overcome by LD-EDT, where synchrotron x-rays previously failed. The resulting structure⁴ is comprised of layers containing edge-sharing Al-O octahedra, inter-connected with As-O tetrahedra by corner sharing. The localization of light atoms in the lattice showcases the potential of electron crystallography for yielding high quality diffraction data even under low dose conditions.

Nowadays, electrochemical energy storage plays a major societal role due to its widespread technological applications. Host nanostructured materials have a crystal structure with insertion sites, channels and/or interlayer spacings allowing the rapid insertion and extraction of lithium ions with generally little lattice strain. Therefore they are used as electrode materials for batteries. Dynamic processes occurring in batteries can be studied by operando modality. Operando experiments provide a realistic representation of the reaction behavior occurring at electrodes, which permits to checking the structural and electronic reversibility of a battery system, while at least one full cycle is performed. For all these reasons, ex situ studies, which reflect a given state of charge (SOC) of electrode materials are now complemented by operando measurements using complementary tools such as X-ray diffraction (XRD) and spectroscopic techniques such as X-ray absorption spectroscopy (XAS).

X-ray absorption spectroscopy is a synchrotron radiation based technique that is able to provide information on local structure and electronic properties in a chemically selective manner. Operando synchrotron radiation x-ray powder diffraction (SR-XRPD) experiments allow monitoring the extended structure of a material during the intercalation/release process of ions.

The potentiality of the joint XAS-XRD approach in the newly proposed Prussian Blue-like cathodes materials for rechargeable batteries is here underlined.

Prussian blue analogous (PBAs) or metal hexacyanoferrates are bimetallic cyanides with a three-dimensional cubic lattice of repeating -Fe-CN-M-NC- units (where M=transition metals). Because of their peculiar structure exhibiting large ionic channels, interstices in the lattice and redox-active sites they have been proposed as active materials for electrodes in batteries. In our group, a series of PBAs have been synthesized, such as copper hexacyanoferrate (CuHCF), manganese hexacyanoferrate (MnHCF), titanium hexacyanoferrate (TiHCF), multi-metal doped hexacyanoferrate, as well as copper nitroprusside etc. In particular, this talk will be summarize results obtained in the case of copper hexacyanoferrate and copper nitroprusside, as well as the manganese hexacyanoferrate [1-5]. Sodium-rich manganese hexacyanoferrate (MnHCF) is gaining consideration as battery materials for the versatility toward several chemistries beyond lithium, the ease of synthesis, as well as their affordable cost of production. MnHCF is constituted only by earth-abundant elements, and it displays high operational voltages and high specific capacities. Since PBAs act as sponge-like materials towards water molecules, also in case of short time exposure to contamination, and both the electrochemical behavior and the reaction dynamics are affected by interstitial/structural water and adsorbed water, the effect of hydration is critical in determining the electrochemical performance. The electrochemical activity of MnHCF without extensive dehydration was investigated by varying the interstitial ion content through a joint approach using operando x-ray absorption fine structure (XAFS) spectroscopy conducted at the XAFS beamline in ELETTRA and multivariate curve resolution with alternating least squares algorithm (MCR-ALS), with the intent to assess the structural and electronic modifications occurring during sodium release and lithium insertion as well as the overall dynamic evolution of the system. The study is also complemented to the and operando XRPD. It was found that only a minor volume change (about 2%) is recorded upon cycling the electrode material against lithium.

[1] A. Mullaliu, G. Aquilanti, P. Conti, J. R. Plaisier, M. Fehse, L. Stievano, M. Giorgetti. Copper Electroactivity in Prussian Blue-Based Cathode Disclosed by Operando XAS. J. Phys. Chem. C, 122 (2018) 15868-15877.

[2] A. Mullaliu, M. Gaboardi, J. Rikkert Plaisier, S. Passerini, M. Giorgetti. Lattice Compensation to Jahn-Teller Distortion in Na-rich Manganese Hexacyanoferrate for Li-ion Storage: An Operando Study. ACS Appl. Energy Mater., 3, (2020) 5728–5733.

[3] A. Mullaliu, J. Asenbauer, G. Aquilanti, S. Passerini, M. Giorgetti. Highlighting the Reversible Manganese Electroactivity in Na-Rich Manganese Hexacyanoferrate Material for Li- and Na-Ion Storage. Small Methods, (2020) 1900529.

[4] M. Li, A. Mullaliu, S. Passerini, M. Giorgetti. Titanium Activation in Prussian Blue Based Electrodes for Na-ion Batteries: A Synthesis and Electrochemical Study. Batteries, 7 (2021) 5.

[5] A. Mullaliu, M.T. Sougrati, N. Louvain, G. Aquilanti, M.L. Doublet, L.Stievano, M. Giorgetti. The electrochemical activity of the nitrosyl ligand in copper nitroprusside: a new possible redox mechanism for lithium battery electrode materials? Electrochimica Acta, 257 (2017) 364–371.

The following researchers are kindly acknowledged: Angelo Mullaliu, Giuliana Aquilanti, Jasper R. Plaisier, Min Li, Stefano Passerini.

The magnetic response of a system is the result of several contributions to the magnetic anisotropy which come from a plethora of effects. In the case of thin ferromagnetic films, the local-scale and long-range structural details, including film thickness, and interface interactions (intermixing, alloying, oxidation etc.) have a deep impact on the magnetism. Once known, these features can be used to tailor the magnetic response of the system, however, to fully control the system response, a deep knowledge is required.

To contrast the high reactivity of some ferromagnetic films, a passivating overlayer can be used: in these cases, further degrees of freedom add up in the definition of the magnetic response due to the upper interface phenomena. A deep understanding of such complex systems requires to assess and isolate the fine details linked to the interactions at the interfaces, and to those occurring within the film itself. Also, the oxidation prevention provided by the capping layer should be verified in view of application purposes.

Such a challenging task can be pursued only by combining complementary, state of the art techniques. This work presents the results of in-situ synchrotron radiation techniques and Magneto-Optic Kerr Effect (MOKE) measurements on Gr/Co/Ir systems, i.e. Co films intercalated between Graphene and Ir(111) [1]. The contributions to the in-plane and out-of-plane magnetic response of the system were evaluated based on Grazing Incidence X-Ray Diffraction (GI-XRD), X-ray Absorption Near Edge Spectroscopy (XANES), and Extended X-ray Absorption Fine Structure (EXAFS). The Gr/Co/Ir system is particularly interesting as the understanding of its magnetic behaviour requires to explore the thickness and thermal dependencies of local-scale and long-range anisotropies, to assess interface intermixing phenomena, and to evaluate the evolution of Co oxidation states (especially upon exposure to ambient conditions).

The development of effective catalytic processes for the conversion of CO₂ into value-added chemicals or fuels, such as methanol synthesis or the dry reforming of methane (DRM) relies strongly on a rational catalyst design, which in turn requires an in-depth understanding of structure-activity relationships. Due to the inherent complexity of heterogeneous catalytic systems, an arsenal of complementary techniques is required to characterize the catalytic structure (and dynamics thereof) from the atomic-to-nanoscale (under reaction conditions). In this talk, we show how the application of combined X-ray powder diffraction (XRD) and X-ray absorption spectroscopy (XAS) allows obtaining the oxidation state, the local and (nano)crystalline structure of the catalysts providing the basis for the formulation of structure-performance relationships in catalysts for CO₂ valorization reactions.

In the first example, we demonstrate how a combined operando XAS-XRD experiment allowed us to relate the evolution of the structure of In₂O₃ nanoparticles (NPs) to their activity for CO₂ hydrogenation to methanol.^[1] The experiments revealed a reductive amorphization of the In₂O_3−x nanocrystallites with time on stream (TOS), leading ultimately to an over-reduction of In₂O_3−x to (molten) In⁰, in a process that is linked to catalyst deactivation. When the In₂O₃ NPs were supported on a nanocrystalline monoclinic ZrO₂ support, we observed the stabilization of the oxidation state of In via the formation of a solid solution m-ZrO₂:In.^[2] In the second example, we explore a Ni-Fe-based catalyst for the DRM. Combined, operando XAS-XRD experiments allowed us to probe the dynamics of Ni-Fe alloying/dealloying with the formation of FeO to explain the superior stability of the NiFe catalysts compared to a Ni-based analogue, due to a Fe-FeO_x-based redox cycle.^[3] In the last example, combined XAS–XRD experiments are used to shed light on the formation of Ru⁰ nanoparticles (ca.1 nm) via their exsolution from defective, fluorite-type Sm₂Ru_xCe_2−xO₇ solid solutions. The resulting exsolved nanoparticles show a high activity and stability for the DRM.^[4]

In this work, we present new geochemical and structural data in order to document a new occurrence of andradite garnet (garnet general formula {X}₃Y₂(Z)₃O₁₂) “demantoid” variety” in Sardinia, Italy [1]. The crystal structure consists of a framework of alternating ZO₄ tetrahedra and YO₆ octahedra that share corners, with cavities in the X cations coordinated by 8 oxygen atoms in the form of a triangular dodecahedron. The yellowish-green to intense green variety of andradite, called “demantoid”, is a precious and greatly appreciated gemstone, mainly found in Russia, Namibia, Madagascar and Italy (Valmalenco, Lumbardy) [2]. The studied samples come from a new deposit from Domus de Maria municipality, nearby “Sa Spinarbedda” mine. This found is very peculiar, because although the beauty of these samples, it has not been previously described from Sardinia region. In this work we investigated the structural and chemical features of these new demantoid samples by combining electron microprobe analyses (EMPA), laser ablation-inductively coupled mass spectrometry (LA-ICP-MS), single crystal X-ray diffraction (XRSD), IR and X-ray absorption (XAS) spectroscopies. Chemical analyses revealed an enrichment of Ca and Fe and a low content of Ti, Mn and Al, thus confirming the andradite nature of the garnet. The Cr content (~8.73 ppm, mean) has been useful to confirm the demantoid variety of andradite. Fe and Mn K-edge XAS data were collected at the XAFS beamline (ELETTRA, Trieste, Italy) both in transmission (Fe) and fluorescence mode (Mn), using fixed exit Si (111) monochromator [4] to better understand the coordination number of both ions. Position of the absorption edge together with the pre-edge peaks analysis, point to the presence of only Fe³⁺ in octahedral coordination, confirming that the whole Fe content can be allocated in the Y crystallographic site. A more complex situation has been found for Mn where pre-edge peaks analysis on our spectrum indicate that Mn should be mainly in the form of Mn²⁺ and 8-fold coordination, occupying the X crystallographic site, beside a small amount of Mn³⁺ is probably present in octahedral Y site. The infrared spectra of andradite crystals investigated at the SISSI beamline (ELETTRA, Trieste, Italy) show a prominent absorption band at about 3560 cm^-1, suggesting the well-known hydrogarnet substitution of (SiO₄)₄ with (O₄H₄)₄ [5][6]. These absorption features are related to hydroxide, which can be incorporated in the andradite structure in the form of structurally bonded OH groups, according to previous experimental findings [5]. X-ray single-crystal diffraction experiments refinement (Ia3̅d space group) highlighted a unit cell volume (1757.15(2)ų) larger than that reported usually in the literature thus confirming the presence of a slight water content [5]. The dodecahedral site X resulted to be partially occupied in a proportion of ≈96.2% Ca and ≈3% of Mn⁺². The octahedral site Y also resulted to be partially occupied in a proportion of ≈95.6% Fe⁺³ and ≈4.5% Al, while the Mn⁺³ content was too low to be estimated. Then, according to Adamo et al. (2011) [6] the potential partial occupation of tetrahedral site has been checked. Actually, the site resulted occupied only for ≈98%, the other 2% has been refined for O (same position and same thermal factor), suggesting the presence of structural water. Refining the site occupancy factor (s.o.f.) at the Si-site, modelled with the scattering curve of silicon alone in the X-ray structure refinement, we obtained s.o.f. value ≈98%, which barely confirmed potential hydrogarnet substitution [i.e., ((SiO₄)₄ with (O₄H₄)₄].

[1] Grew, Edward & Locock, A. & Mills, S.J. & Galuskina, Irina & Galuskin, Evgeny & Hålenius, Ulf. (2013). Am. Min. 98, 785-811.

[2] Štubňa, J., Bačík, P., Fridrichová, J., Hanus, R., Illášová, Ľ., Milovská, S., ... & Čerňanský, S. (2019). Minerals, 9(3), 164

[3] Geiger, C. A., & Rossman, G. R. (2020). Am. Min. 105(4), 455–467

[4] Di Cicco, A., Aquilanti, G., Minicucci, M., Principi, E., Novello, N., Cognigni, A., & Olivi, L. (2009). J. Phys. Conf. Ser. 190(1), 012043

[5] Amthauer, G. & Rossman, G.R. (1998): The hydrous component in andradite garnet. Am. Mineral., 83, 835–840.

[6] Adamo, I., Gatta, G. D., Rotiroti, N., Diella, V., & Pavese, A. (2011). Eur. J. Mineral. 23(1), 91-100

LiFePO₄ (LFP) as a cathode material in lithium ion batteries has a number of advantages including a long cycle life, a long calendar life and can be used at high discharge currents. A low cost, low energy hydrothermal synthetic route is being investigated where homemade Teflon bombs are used in an oven at 120^oC to synthesise LFP. During synthesis an aqueous LiOH solution is added dropwise to a FeSO₄–H₃PO₄ solution. All solutions are constantly purged with nitrogen during this step to prevent any oxidation. Interestingly it was determine that the rate at which the Li⁺ solution was added to the Fe²⁺ solution (while being stirred at a constant speed) influenced the final product. The addition rate was set to one drop every 1, 2, 3, 4 and 5 seconds. If the Li⁺ was added too slowly a mixture of phases (LFP and Li₃PO₄) was formed and when it was added too fast a completely different final phase was formed. In the latter case no LFP was identified using PXRD, but raman spectroscopy (RS) showed that non-crystalline LFP was present in the sample together with other phases.

A range of different techniques have been combined to probe the effect of the different addition rates on the local and average environments. It was determined that the 3sec addition rate was the optimum rate. Synchrotron X-ray diffraction (SXRD) with Rietveld refinement was used to characterize the average structures of the different environments (Figure 1). Mössbauer spectroscopy (MS) was used to probe the effect of Li⁺ addition on the local environment. Although no impure phases were identified using SXRD in the samples synthesised with the optimum addition rate, MS indicated that there was amorphous phases present. MS also showed that there was more than one Fe environment present in the sample. The major phase was Fe²⁺ in a distorted octahedral environment (LiFePO₄). The other 3 contributions to the total Fe in the sample are due to either structural defects, distortions or disorder [1]. X-ray absorption spectroscopy (XAS), in particular extended X-ray absorption fine structure (EXAFS) (Figure 2) was used to determine what the effect of the different addition rates on the local structure is.

Noble metal nanoparticles, due to their relatively high stability and wide scope of application, attract a lot of researchers’ attention. The catalyst effectiveness directly depends on the dispersion rate and the presence of active catalytic sites, since the higher the dispersion, the greater the surface area available for catalytic reactions. The substrate material also plays a large role in the efficiency of the final product. One of the new and effective methods for the synthesis of the noble metals ultrafine nanoparticles is UV irradiation of their precursor salts. The main advantages of this method are relative simplicity, high recovery rate and environmental friendliness. The nanoparticles synthesized in this way are less susceptible to agglomeration, which eliminates the need for introducing various surfactants and toxic solvents into the system, in contrast to standard methods. Due to the relatively high value of the electrode potential of the Pd²⁺/Pd⁰ pair, as well as low photostability, complex palladium salts are quite easily restored, and the selection of the optimal salt and radiation power allows the process to be rapidly carried out.

In this work, palladium nanoparticles were synthesized in an aqueous solution by UV irradiation using complex palladium oxalate as a precursor. The synthesis consists of UV irradiation of an aqueous dispersion of CeO₂ containing the [Pd(C₂O₄)₂]^2– complex as one of the most photoactive non-toxic precursors. Cerium dioxide was synthesized by a simple one-step method and was selected due to its high thermal stability and relative chemical inertness, as well as its large oxygen storage capacity due to the formation of the Ce⁴⁺/Ce³⁺ redox pair, which allows CeO₂ to efficiently release catalytically active oxygen species. Samples were studied by various laboratory methods, such as TEM, XRF, XRPD, XAFS spectroscopy, and diffuse reflection IR spectroscopy of CO probing molecules.

TEM images did not allow to distinguish Pd nanoparticles from the substrate material but showed the absence of the UV radiation influence on the sizes of CeO₂ nanoparticles. XRF data showed the presence of cerium and palladium atoms in the material. X-ray diffraction patterns indicate the presence of both a cerium dioxide phase and a phase of metallic palladium, while the analysis of XAFS spectra beyond the K edge of palladium also showed the presence of a PdO phase in the system (Fig. 1). The approximate size of palladium nanoparticles was estimated from the infrared spectra after CO adsorption (Fig. 2) and it was less than 2 nm, which is significantly smaller than the average size of Pd nanoparticles obtained by a similar method without a CeO₂ substrate (1.5–9.5 nm) [1].

[1] Navaladian, S., Viswanathan, B., Varadarajan, T. K., & Viswanath, R. P. (2008). Nanoscale research letters 4(2), 181.

The work was supported by grant of President of Russia for young scientists (MK-2730.2019.2).

A description and understanding of the local atomic and electronic structure is essential for knowledge – based design of advanced materials. X-ray absorption spectroscopy (XAS) and related techniques can play a crucial role in this context, allowing an atomistic understanding of materials function. In this talk I will review recent advances in the application of XAS and related techniques to materials for photocatalysis.

TiO₂ is one of the most studied oxide semiconductors for photocatalysis. However, because of its wide band gap only a small fraction of the solar spectrum can be harvested. This limitation can be overcome by doping or inclusion of metallic nanoparticles. By using XAS, including ab – initio full potential simulations, we have shown that V dopants in TiO₂ nanoparticles and thin films occupy substitutional sites, irrespective of whether the oxide matrix has a rutile, anatase or mixed structure; N dopants, instead, are found both in substitutional anionic sites and as N₂ dimers [1, 2]. These structural studies are complemented with a quantification of materials functionality, correlated to the charge carrier dynamics studied by ultra fast optical spectroscopy [3]. We have also applied a high resolution XAS method with differential illumination to prove that sub-bandgap visible light absorption is predominantly due to excitation of electrons from V ions to defective and long-lived Ti sites, thus identifying an element-specific photoexcitation channel [4]. Inclusion of metallic nanoparticles in the oxide matrix extends light absorption to the visibile range thanks to the excitation of the surface plasmon resonance. By using high resolution XAS in TiO₂ sensitized by Au nanoparticles, we have demonstrated charge transfer from Au nanoparticles to long – lived states localized on defective sites localized on the oxide surface [5].

Inclusion of plasmonic nanoparticles can be used also to sensitize CeO₂, a photocatalyst characterized by the ability of Ce to reversibly change between the 4+ and 3+ oxidation states. Using static XAS we have performed an in - depth structural investigation of CeO₂ nanoparticles [6] and of Ag nanoparticles on the CeO₂ surface [7]. More recently, using time resolved XAS with ~ 100 fs time resolution using the FERMI free electron laser, we have demonstrated electron trasfer from plasmonic Ag nanoparticles to the CeO₂ matrix [8].

[1] Rossi et al., J. Phys. Chem. C 2016, 120, 7457−7466. DOI: 10.1021/acs.jpcc.5b12045

[2] El Koura et al., Phys.Chem.Chem.Phys., 2018, 20, 221. DOI: 10.1039/c7cp06742a

[3] Rossi et al., Applied Catalysis B: Environmental 237 (2018) 603–612. DOI: 10.1016/j.apcatb.2018.06.011

[4] Rossi et al., Phys. Rev. B 96, 045303 (2017). DOI: 10.1103/PhysRevB.96.045303

[5] Amidani et al., Angew. Chem. Int. Ed. 2015, 54, 5413 –5416. DOI: 10.1002/anie.201412030

[6] Benedetti et al., J. Phys. Chem. C 2015, 119, 6024−6032. DOI: 10.1021/jp5120527

[7] Pelli Cresi et al., Nanotechnology 28 (2017) 495702. DOI: 10.1088/1361-6528/aa926f

[8] Pelli Cresi et al., Nano Lett. 2021, 21, 1729−1734. DOI: 10.1021/acs.nanolett.0c04547

Room-temperature superconductivity has been a century long-held dream of mankind and a focus of intensive research. Recent progress on findings of room-temperature superconductors among superhydrides stabilized at high pressure conditions is remarkable. Focus is placed on a class of clathrate superhydrides, the best ever-known family of superconductors, that exhibit extraordinarily high-T_c superconductivity (e.g., T_c = 260 K for LaH₁₀ [1-4]).

The first-ever clathrate structure in superhydride is proposed in CaH₆ [5] by my group that shows a potential of high-T_c superconductivity at about 235 K. This clathrate structure accepts the emergence of unusual H cages, in which H atoms are weakly covalently bonded to one another, with Ca atoms occupying the centers of the cages. The high-T_c superconductivity is arising from the peculiar H clathrate structure.

We recently found a common rule of the formation of superconducting clathrate structures in rare earth (RE, e.g., Sc, Y, La, Ce, Pr., etc) superhydrides accompanying the occurrence of three different stoichiometries of REH₆, REH₉, and REH₁₀, some of which exhibit extraordinarily high-T_c superconductivity [1]. Subsequent experiments [3,4,6,7] indeed synthesized the as-predicted clathrate superhydrides YH₆, YH₉, and LaH₁₀ with measured T_c values at 224, 243, and 260 K, respectively, setting up new T_c records among known superconductors. These discoveries open the door of achieving superconductors that could work at room temperature (300 K) in superhydrides.

In the talk, I will give an overview on the status of research progress on superconductive superhydrides, and then discuss the design principle for achieving room-temperature superconductor. Our prediction on a hot superconductor (T_c at ~400 K) in a clathrate superhydride Li₂MgH₁₆ [8] together with future research direction will be discussed.

References:

[1] Peng et al., PRL 119, 107001 (2017).

[2] Liu et al., PNAS 114, 6990 (2017).

[3] Somayazulu et al., PRL 122, 027001 (2019).

[4] Drozdov et al., Nature 569, 528 (2019).

[5] Wang et al., PNAS 109, 6463 (2012).

[6] Kong et al., arXiv 1909.10482 (2019) ; Snider et al., PRL 126, 117003 (2021).

[7] Troyan et al., Adv. Mater. 33, 2006832 (2021).

[8] Sun et al., PRL 123, 097001 (2019).

Nanocarbon materials show attractive functions in device applications, however the structural deviations and ambiguity disturb understanding between the functions and the structures. We have worked on the synthesis of molecular nanocarbon materials based on a simple strategy of macrocyclization of aromatic units. The molecular structures and supramolecular integrated structures can be fully accessed at the precision of molecular level, and unparalleled functions derived from the unique structures were found.

For example, a macrocyclic hydrocarbon molecule, [6]cyclo-2,7-naphthylene ([6]CNAP), synthesized by single bond linkage of six naphthylene units (Figure 1a) has a cyclic structure equivalent to an atom-defective structure of graphene [1]. In this study, [6]CNAP was applied to a negative electrode active material for a rechargeable lithium battery, where graphite is conventionally and commercially used as the material. All-solid-state lithium battery with LiBH₄ as electrolyte was constructed with three layers simply by uni-directional pressing: the composite electrode with [6]CNAP, acetylene black (AB) and LiBH₄ | LiBH₄ | Li (Figure 1b and c). Depending on purification methods, the recyclability of the rechargeable batteries largely differed. Surprisingly, highly purified specimen by sublimation method showed poor recyclability, and the recrystallized specimen from organic solvents showed stable recyclability up to 65 discharge-charge cycles and around twice battery capacity than a graphite electrode. We found that the differences in battery performance were originated from the molecular packing structures in solid states by powder X-ray structural analyses with Rietveld refinement. The key for the high battery performance is the one-dimensional nanopores constructed from the assembly of the central pore of [6]CNAP and π-stacks of naphthylene units. The quantitative battery performance results and the precisely determined packing structures showed that lithium ion is stored by the intercalation between naphthylene units and also in the one-dimensional nanopores to afford the high battery capacity. We successfully revealed the relationship between unique packing structures and battery performance [2].

[1] Nakanishi, W., Yoshioka, T., Taka, H., Xue, J. Y., Kita, H. & Isobe, H. (2011). Angew. Chem. Int. Ed. 50, 5323.

[2] Sato, S., Unemoto, A., Ikeda, T., Orimo, S. & Isobe, H. (2016). Small 12, 3381.

Recently, the traditional way of perceiving crystalline matter as static and brittle has started to change, and nowadays we are witnessing a growing number of examples where crystals display a plethora of flexible response to a variety of stimuli. They were found to move, jump, split, flex, twist, curl, explode, or to display a salient behaviour under UV radiation or heating, but lately, they were also found to respond to the applied external mechanical force [1]. Organic molecular crystals present a majority of examples of crystal adaptability to external stimuli, whilst metal-organic adaptable crystals are still quite rare. In the first report on the mechanical flexibility of coordination polymers, we have shown that crystals of a family of Cd(II) coordination polymers are capable of displaying not only exceptional mechanical elasticity but also variable flexible responses to applied external pressure [2]. They can actually differently tolerate exerted force and the different tolerability is a result of slight differences in the importance of intermolecular interactions in crystal packing.

We aim to understand the feature more deeply and to shed light on the underlying principles of the phenomenon, we have recently discovered unprecedented difference in plasticity of crystals of closely related class of Cd(II) coordination polymers [3]. In addition to variable plasticity, crystals also display remarkable pliability and ductility, not hitherto observed for metal-containing molecular crystals, which we present herein. To understand the phenomenon and rationalize observations, in addition to micro-focus SCXRD and AFM, we have also performed a series of custom-designed experiments and complemented those with an in-depth theoretical analysis. The results pointed at intermolecular interactions as the crucial structural feature in determining the type and extent of these highly unusual mechanical responses of crystalline metal-based polymeric materials.

[1] Commins, P., Israel Tilahun Desta,†Durga Prasad Karothu,† Panda, M. K. & Naumov, P. (2016) Chem. Commun. 52,13941.

[2] Đaković, M., Borovina, M., Pisačić, M., Aakeröy, C. B., Soldin, Ž., Kukovec., B.-M., Kodrin, I. (2018) Angew. Chem. Int. Ed. 130, 15017.

[3] Pisačić, M., Biljan, I., Kodrin, I., Popov, N., Soldin, Ž., Đaković, M. Chem. Mat. accepted.

This work has been fully supported by the Croatian Science Foundation under Project IP-2019-04-1242.

At present, the functional materials structurally switchable by stimuli such as heat, the addition of cations, changes of pH, pressure, or light are the motive of innumerable studies to be ideal models to investigate the relation structure-function and new properties derived from that change. In this work, we studied a family of spirorhodamines (SRAs) in solid-state photochemical reactions. These are photochromic molecules with a switching mechanism based on the differences in the fundamental electronic state between isomers.[1] It involves changes in the molecule structure and is thermally reversible.[2,3] In this work, assuming as the hypothesis that in solid-phase the permanence time in the optically active isomer is associated with its structural characteristics, a family of compounds modifying the substituent was synthesized.

These equilibria were characterized in solid-state by reflection, absorption and emission fluorescence spectroscopy, single-crystal X-ray diffraction,[4] atomic force microscopy coupled to infrared spectroscopy[4] and computational calculations, evaluating the changes produced after irradiating the corresponding close isomer with ultraviolet light for each compound.

[1] Dürr, H., Bouas-Laurent, H. (2003) Photochromism: Molecules and Systems, Eds.

[2] Di Paolo, M., Bossi, M. L., Baggio, R. and Suarez, S. A. (2016) Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater., 72, 684.

[3] Di Paolo, M., Boubeta, F., Alday, J., Michel Torino, M., Aramendía, P., Suarez, S.* and Bossi, M.* (2019) J. Photochem. Photobiol. A,. 384, 112011.

[4] Brazilian Synchrotron Light Laboratory (LNLS) beamlines MX2 and IR1.

In this work, the effects of pressure and temperature on the nonlocalized two-electron multicentric covalent bonds (‘pancake bonding’) in closely bound radical dimers were probed by single-crystal X-ray diffraction on a 4-cyano-N-methylpyridinium salt of 5,6-dichloro-2,3-dicyanosemiquinone (DDQ∙4CN) and I-methylpyridinium salt of tetrabromosemiquinone radical anion (Br₄Q∙NMePyr) as the sample compounds.

The DDQ∙4CN crystal structure can be described as closely bound stacked dimers of radical anions with interplanar separation <3.2 Å, which is known as non-localized two electron covalent bonding. At ambient conditions, the stacks of pancake bonded radical anions are formed by two types of distances: short intra-dimer and long inter-dimer contacts. On cooling, the anisotropic structural compression was accompanied by continuous changes in molecular stacking; the discontinuities in the changes in volume and b and c cell parameters suggest that a phase transformation occurs between 210 and 240 K. At a pressure of 2.55 GPa, both distances between radical dimers shortened to 2.9 Å, and become roughly equal, which corresponds to distances observed in extended-bonded polymers. Increasing pressure further to 6 GPa reduced the interplanar separation of the radicals to 2.75 Å, which may indicate that the covalent component of the interaction significantly increased [1]. The linear strain analysis shows that most deformations of pressure and temperature occur in the direction of pancake bonding.

The Br₄Q∙NMePyr crystal structure is built of infinite stacks of equidistant radical anions with no Peierls distortion [2]. On cooling the structure is compressed monotonically, the distance between radicals changes non-linearly, compress to <3.3 Å, but the space group remains the same. Upon pressure, the structure is compressed monotonically with no phase transformations in all the pressure range (0 – 6.0 GPa), the lowest interplanar distance is <2.9 GPa, which may indicate the increase of the covalent component in pancake bond and a significant decrease of the electron jumping barrier which may influence semiconductivity.

Azulene is a dark-blue, polar, bicyclic aromatic hydrocarbon (Figure 1) that is a non-benzenoid isomer of naphthalene. In addition to its long-standing medicinal and pharmaceutical relevance, the polar nonbenzenoid aromatic framework of azulene constitutes an attractive building block in the design of redox-addressable, optoelectronic, and conductive materials. This presentation will highlight our recent developments in the chemistry of hybrid metal/azulene platforms featuring isocyanide and thiolate junctions X along their molecular axis (Figure 2).

Figure 1. Electronic structure of azulene: resonance forms Figure 2. Two ways of functionalization of azulene at 2- and and origin of a molecular dipole. 6- positions that are important for its fixation on a solid support.

Single crystal X-ray structural analysis of a series of novel 2,6-functionalized azulenes will be presented [1,2]. In particular, heterobimetallic ensembles that incorporate the first examples of a conjugated p-bridge equipped with both isocyanide and thiol junction groups in the same molecular linker will be discussed (e.g., Figure 3B).

Figure 3. Two different functional groups – isonitrile and thiol – used for chemical modification of azulenes.

[1] Applegate, J.C.; Okeowo, M.K.; Erickson, N.R.; Neal, B.M.; Berrie, C.L.; Gerasimchuk, N.N.; Barybin, M.V. (2016) Chem. Sci., 7, 1422–1429. [2] Hart, M.D.; Meyers, J.J.; Wood, Z.A.; Nakakita, T.; Applegate, J.C.; Erickson, N.R.; Gerasimchuk, N.N.; Barybin, M.V. (2021). Molecules, 26, 981. https://doi.org/10.3390/molecules26040981

To investigate the salt formation of acridine with 4-amino salicylic acid (I), 5-chloro salicylic acid (II) and hippuric acid (III), the single crystal X-ray structure analysis have been performed. The present study allows to understandthe effect of molecular conformation adopted by acridine with hydroxyl group during the stabilization of crystal packing of these salt molecules, and to quantify the propensity of the intermolecular interactions to form the supramolecular assembly. The analysis of atom to atom or residue to residue contacts remains a favoured mode of analyzing the molecular packing in crystals. More importantly, they complement each other and are giving the complete picture of how these molecules assemble in molecular crystals. Hirshfeld surfaces, fingerprint plots and enrichment ratios were generated and further analyzedthe intermolecular interactions, and evaluatedtheir quantitative contributions to the crystal packing of the above saidthree salt molecules (I,II & III). The non-covalent interactionisosurfaceshave employed here, which allowsvisualizing where the hydrogen bonding and dispersion interactions contribute within the crystal.

The structure of liquid and glass is usually described by the atomic pair-distribution function (PDF), g(r), which expresses the statistical distribution of distances between atoms. The PDF can be determined by diffraction experiments using x-rays or neutrons. However, liquid is dynamic in nature, and we have to be sensible about what the PDF means for liquid. For crystalline solids the atomic structure is determined by the elastic scattering of x-rays, neutrons or electrons, because the momentum is transferred to the whole rigid body of the sample in scattering. But the elastic scattering intensity from liquid is zero because of the lack of rigidity. The scattering from liquid is purely inelastic, described by the dynamic structure factor, S(Q, ω), where Q is the momentum transfer and E = hω/2π is the energy transfer in scattering. To measure S(Q, ω) we need an elaborate inelastic scattering instruments. In particular for inelastic x-ray scattering (IXS) we need a very high energy resolution with ~ meV and ΔE/E < 10^-7. This can be achieved only with a large backscattering crystal analyzer with a long flight path. However, in regular x-ray diffraction measurement the energy resolution is poor, ~ 1 eV, far exceeding the typical energies of vibrational excitations. As a result, the measured structure function, S(Q), is the S(Q, ω) integrated over energy, thus representing the same-time correlation among atoms. Thus, the PDF, obtained by the Fourier-transformation of S(Q), is the same-time density correlation function which shows the time averaged snapshot of correlations. Therefore, the PDF does not describe the structure in a regular sense. For a long time, the PDF has been used in representing the structure, because it was the only readily available structural descriptor, and various theories have been proposed to predict dynamic properties from the PDF. On the other hand, the dynamic two-body correlation can be directly expressed by the Van Hove function, G(r, t), obtained by the double-Fourier-transformation of S(Q, ω). But, to carry out the double-Fourier-transformation accurately S(Q, ω) has to be measured over a wide Q-E space. Until recently this was unpractical, because the inelastic scattering measurement, typically done with a triple-axis-spectrometer, was extremely time-consuming. But the advent of pulsed neutron sources with large two-dimensional detector arrays and advances in the IXS instrumentation made it possible to determine the Van Hove function in a reasonable time, 4 – 12 hrs. We applied this technique to various liquids, including water, aqueous solutions of salt, metallic alloy liquids, liquid Ga, and organic electrolytes. New physical insights obtained by these measurements will be discussed. Now that this technique is available we should expand the definition of the “structure” of liquid to include the dynamic structure represented by the Van Hove function.

Pd_42.5Ni_7.5Cu₃₀P₂₀ (PNCP) has at present the most excellent glass-forming ability (GFA) among metallic glasses. The critical cooling rate (CCR) reaches of 0.067 K/s and can form a massive bulk glass with a diameter of more than 40 mm [1]. On the other hand, almost the parent alloys of Pd₄₀Ni₄₀P₂₀ (PNP) and Pd₄₀Cu₄₀P₂₀ (PCP) have worse CCRs of about 1 K/s [2] and 100 K/s [3], respectively, indicating that the mixture of Ni and Cu elements causes a better CCR in these bulk metallic glassy alloys.

In order to find a structural origin of the GFAs of these Pd-based glasses, we have carried out anomalous x-ray scattering (AXS) and neutron diffraction (ND) experiments on PNP [4], PCP [5], and PNCP (preliminary results were given in [6]), and the experimental results were analysed by using reverse Monte Carlo (RMC) modelling. The obtained atomic configurations of these alloys were discussed by using a Voronoi tessellation for the short-range atomic arrangements and a persistent homology analysis [7] for the hyper-ordered atomic structures.

Although the general features of the atomic configurations look similar to one another, i.e., most of atomic configurations around all elements are basically icosahedral-type, the main results of these analyses are as follows:

1) A large fraction of “pure” icosahedra are observed around only Ni atoms (5.8%) in PNP [4], whereas that around Cu in PCP is a half value of 2.9% [5]. Very interestingly in PNCP, large fractions of “pure” icosahedra are detected not only around the Ni atoms of 4.8%, but around the Cu atoms of 5.6%.

2) Large sizes of partial persistent homology rings are observed for the Ni/Cu atoms in all the glasses. However, the size highly depends on the GFA of the glasses, i.e., that in PNCP is slightly larger than in PNP, and much larger than in PCP.

In conclusion, the GFA of Pd-based metallic glasses is not understood as clearly characterized structures such as the existence of clusters of crystal-like fragments. It is realized through hyper-ordered structures, i.e., profound structural features in the short- and intermediate-range atomic order in the glasses.

[1] Nishiyama, N. and Inoue, A., (2002), Appl. Phys. Lett. 80, 568.[2] Drehman, A. J., Greer, A. L., and Turnbull, D., (1982). Appl. Phys. Lett. 41, 716.[3] He, Y. and Schwarz, R. B., (1997), Mater. Res. Symp. Proc. 455, 495.[4] Hosokawa, S. et al., (2019). Phys. Rev. B 100, 054204.[5] Hosokawa, S. et al., (2021), J. Non-Cryst. Solids 555, 120536.[6] Hosokawa, S. et al., (2009), Phys. Rev. B 80, 174204.[7] Hiraoka, T. et al., (2016), Proc. Natl. Acad. Sci. USA 113, 7035.

When sample conditions for conventional crystallography are not met (i.e. a large, well-ordered crystal) then x-ray diffraction techniques often do not yield an unambiguous 3D atomic structure. This can occur in powder diffraction and small-angle x-ray scattering (SAXS), where ensembles of crystals or particles in random orientations produce isotropic diffraction around the beam axis. It also occurs for disordered materials, such amorphous solids and liquids, where randomness at the molecular scale has a similar suppression of accessible structural information via x-ray scattering. The accessible structural information is the distribution of atom-pair distances (known as the pair distribution function or PDF). The PDF has no information about local angular structure, such as bond angles, and in many cases does not uniquely determine the 3D structure.

Fluctuation x-ray scattering (FXS) [1,2] aims to measure the local angular structure in disordered materials using a small x-ray beam to enhance angular scattering fluctuations. We have developed a method of inverting FXS data to recover a sum of three- and four-atom distributions in real-space[3]. We call this 3D function the Pair-Angle Distribution Function (PADF). It is a natural generalisation of the widely used PDF to higher dimensions. The PADF contains, for example, a bond angle distribution and massively increases the amount of structural information beyond that of the PDF.

There are exciting opportunities to combine PADF analysis with crystallography, powder diffraction and SAXS. It could yield new routes to crystal structures, nanoscale disorder, amorphous structure and liquid structure. Here we give an introduction to the PADF and report on our early experimental results with synchrotron, x-ray free-electron lasers and electron microscopes. These include applications to self-assembled lipids[4], disordered carbon materials[5], protein crystals[6] and liquids.

[1] Kurta, R.P., Altarelli, M. and Vartanyants, I.A. (2016). “Structural analysis by x-ray intensity angular cross-correlations” in Advances in Chemical Physics (eds S.A. Rice and A.R. Dinner).

[2] Kam, Z. (1977). Macromolecules, 10(5), 927–934.

[3] Martin, A. V. (2017). IUCrJ, 4, 24–36.

[4] Martin, A. V., et al., (2020). Small, 2000828, 1–6

[5] Martin, A. V., et al., (2020). Communications Materials, 1(40), 1–8.

[6] Adams, P.,, et al., (2020). Crystals, 10, 724.

Commonly classical nucleation theory has been used to explain nucleation, but this is now being challenged as atomic scale techniques has been developed to study solutions showing larger clusters before nucleation [1, 2]. Thus, a new theory including these clusters with predictive value is needed. To achieve this, it is essential to investigate the atomic structure of precursors across different elements as well as chemical environments.

In this study the precursors of group 13 metal oxides have been examined. Al, In and Ga form similar oxides and hydroxides such as M(OH)₃, MOOH and M₂O₃ in solvothermal synthesis. The individual systems exhibit complex polymorphism, which can be controlled with different synthesis parameters such as solvent and temperature, however, the actual mechanisms are unknown.

The precursor structures of the group 13 metal oxides have been determined by combining PDF and EXAFS analysis of the three metal nitrates in various solvents. Across element and solvents the structures were determined to be octahedrally coordinated metal-oxygen with further structure.[3] For the gallium system variation of pH, anions and concentration were further investigated using PDF analysis revealing the diverse solution chemistry of gallium [4].

Based on the results, the formation mechanisms of the group 13 metal oxides are discussed, for example reason for the production of AlOOH at most synthesis conditions instead of the desirable γ-Al₂O₃ phase [3,5].

Figure 1. Modelling of both EXAFS and PDF data for the same models.

[1] Bøjesen, E. D. & Iversen, B. B. (2016). CrystEngComm. 43, 8332-8353 [2] Gebauer, D., Kellermeier, M., Gale, J. D., Bergström, L. & Cölfen, H. (2014). Chem. Soc. Rev. 43, 2348-2371. [3] Sommer, S., Nielsen, I. G. & Iversen, B. B. (2020). Chem. – Eur. J. 26, 1022-1026. [4] Nielsen, I. G., Sommer, S., Dippel, A.-C. Skibsted, J. & Iversen, B. B. (2021). Submitted to JACS. [5] Nielsen, I. G., Sommer, S. & Iversen, B. B. (2021). Nanoscale 13, 4038-4050.

Due to its sensitivity to local structure, X-ray absorption spectroscopy is a powerful tool to study disordered systems. One of the most interesting property of XAFS is the sensitivity not only to pair distribution function, but also to three-body distribution, which contains information on bond angles between nearest neighbours. Reverse Monte Carlo (RMC) is a structural modelling method from which this information can be obtained [1], but it requires to know the density of the system being investigated, which may not be available especially in extreme thermodynamic conditions. Being a simulation method, it is also costly in terms of time. In recent years, neural networks (NN) have become a widely used tool to tackle different problems and have also been applied to the analysis of EXAFS data [2]. We wanted to investigate whether the same methodology could be applied to disordered systems and whether it would be possible to obtain information beyond the pair distribution function.

The critical point of any NN is the dataset used for the training process, that should be sufficiently large and heterogeneous. For this purpose, we ran several MD simulations of mono-atomic nickel at various temperatures for different crystal configurations, varying also the first-neighbour distance. The temperature was increased past the melting point to also include liquid configurations. From each configuration, we calculated the number distribution function, bond-angle distribution of the nearest neighbours and the EXAFS signal, using GNXAS suite of programs [3]. The created dataset was then used to optimize and train a set of deep NN to estimate number and bond-angle distribution from a given EXAFS signal.

We used the NN to analyse data of nickel at different temperatures and phases. Results from each NN are averaged and standard deviation calculated to estimate errors. Obtained results show that the NN is able to distinguish between ordered and disordered configurations and is also able to detect small changes in the local ordering of liquid structure, comparable with previously published results [4].

[1] Di Cicco A., Trapananti A., Faggioni S. & Filipponi A. (2003). Phys. Rev. Lett. 91, 135505.

[2] Timoshenko J., Anspoks A., Cintins A., Kuzmin A., Purans J. & Frenkel A. I. (2018). Phys. Rev. Lett. 120, 225502.

[3] Filipponi A. & Di Cicco A. (1995). Phys. Rev. B 52, 15135.

[4] Di Cicco A., Iesari F., De Panfilis S., Celino M., Giusepponi S. & Filipponi A. (2014). Phys. Rev. B 89, 060102.

Molecules and molecular ions, unlike individual atoms, have rotational degrees of freedom. This simple observation means that they can be particularly good building blocks for disordered crystal structures. Such behaviour is not merely a crystallographic curiosity: it is responsible for many important materials properties. For instance, if, in some material, a molecule with a permanent dipole moment is free to rotate at high temperatures but freezes into place at low temperatures, the two phases will have different entropies and dielectric constants. The result will be a dielectric switching material; it is likely to be an electro- and/or barocaloric, where the phase transition responds to an external electric field or pressure; and it may also be pyro- and even ferroelectric if the low-symmetry phase is polar.

Studying such materials requires a combination of experimental and computational techniques. Traditional crystallographic methods remain vital, but entail a time and space average that can obscure the behaviour of the disordered phase. Thus it is also important to use methods such as total scattering, which are sensitive to local deviations from that average; and to study also the dynamics, or how structures change over time. Neutron scattering methods are especially appropriate because they reveal the behaviour of hydrogen atoms, which is essential to understanding these rotating molecules, and provide both structural and dynamic information.

A particular focus of recent interest has been the family of molecular perovskites, in which molecular ions on the “A” site almost always display this sort of order-disorder transition [1]. This site is a cubic interstice of the perovskite framework, which provides both structural stability and the freedom for the ions to rotate. But of course order-disorder behaviour does not require this specific coordination framework, or indeed any framework at all: similar molecular “scaffolding” can be provided by other weak interactions, including van der Waals and hydrogen bonding.

Here we compare “free” to “caged” molecules and molecular ions that undergo entropic transitions. We consider the cyanide-bridged elpasolite (double perovskite) analogues (C₃H₅N₂)₂K[M(CN)₆], C₃H₅N₂ = imidazolium, M = Fe, Co [2]; the molecular material adamantane, C₁₀H₁₆ [3], and the molecular-ionic compound ammonium sulfate, (NH₄)₂SO₄ [4]. We have studied these materials’ structure by Bragg and total neutron scattering, and their dynamics by inelastic and quasielastic neutron scattering, complemented by density-functional theory simulations. Combining these methods provides a detailed picture of the actual rotational and vibrational freedom that molecules have in these materials, and hence of the structural origins of their useful properties. In particular, we show that the limiting cases of free rotation and harmonic oscillation can both be inaccurate and even seriously misleading, with the true situation lying somewhere between these extremes. Our results will direct future attempts at “entropic engineering”: designing molecular materials to have specific order-disorder behaviour.

[1] Kieslich, G. & Goodwin, A. L. (2017). Mater. Horiz. 4, 362–366.

[2] Duncan, H. D., Beake, E. O. R., Playford, H. Y., Dove, M. T. & Phillips, A. E. (2017). CrystEngComm 19, 7316–7321; Phillips, A. E. & Fortes, A. D. (2017). Angew. Chem. Int. Ed. 56, 15950–15953; Phillips, A. E., Cai, G. & Demmel, F. (2020). Chem. Commun. 56, 11791–11794.

[3] Beake, E. O. R., Tucker, M. G., Dove, M. T. & Phillips, A. E. (2017). ChemPhysChem 18, 459–464.

[4] Cai, G. (2020). Studying orientational disorder with neutron total scattering, Ph.D. thesis, Queen Mary University of London, U.K.

Most research on polyoxometalates (POMs) has been devoted to synthetic compounds. However, recent mineralogical discoveries of POMs in mineral structures demonstrate their importance in geochemical systems. In total, fifteen different types of POM nanoscale size clusters in minerals have been found that occur in forty-three different mineral species. The topological diversity of POM clusters in minerals is rather restricted compared to the multitude of moieties reported for synthetic compounds, but the lists of synthetic and natural POMs do not overlap completely. The metal-oxo clusters in the crystal structures of the vanarsite-group minerals ([As³⁺V⁴⁺₂V⁵⁺₁₀As⁵⁺₆O₅₁]^7-), bouazzerite and whitecapsite ([M³⁺₃Fe₇(AsO₄)₉O_8-n(OH)_n]), putnisite ([Cr³⁺₈(OH)₁₆(CO₃)₈]^8-), and ewingite ([(UO₂)₂₄(CO₃)₃₀O₄(OH)₁₂(H₂O)₈]^32-) contain metal-oxo clusters that have no close chemical or topological analogues in synthetic chemistry. The interesting feature of the POM cluster topologies in minerals is the presence of unusual coordination of metal atoms enforced by the topological restraints imposed upon the cluster geometry (the cubic coordination of Fe³⁺ and Ti⁴⁺ ions in arsmirandite and lehmannite, respectively, and the trigonal prismatic coordination of Fe³⁺ in bouazzerite and whitecapsite). Complexity analysis indicates that ewingite and morrisonite are the first and the second most structurally complex minerals known so far. The formation of nanoscale clusters can be viewed as one of the leading mechanisms of generating structural complexity in both minerals and synthetic inorganic crystalline compounds. The discovery of POM minerals is one of the specific landmarks of descriptive mineralogy and mineralogical crystallography of our time.

The development of light, long-lasting rechargeable batteries (and the invention of the lithium-ion battery, now over 25 years ago) has been an integral part of the portable electronics revolution. This revolution has transformed the way in which we communicate and transfer and access data globally. Rechargeable batteries are now playing an increasingly important role in transport and grid applications, but the introduction of these devices comes with different sets of challenges. Importantly, fundamental science is key to producing non-incremental advances and to develop new strategies for energy storage and conversion.

The talk will focus on our work to develop and apply methods that allow devices to be probed while they are operating (i.e., in-situ). This allows the transformations of the various cell components to be followed under realistic conditions without having to disassemble and take apart the cell. To this end, the application of new in and ex-situ Nuclear Magnetic Resonance (NMR), and X-ray diffraction (XRD) approaches to correlate structure and dynamics with function in lithium- and sodium-ion batteries and supercapacitors will be described. To illustrate, we have used NMR, theory and pair distribution function (PDF) analysis methods, to determine the local and longer-range structures of a series of amorphous and disordered Li and Na anode structures, including C, Sn, Ge, Si and P. Both thermodynamic and metastable phases are identified via theoretical (DFT) approaches and compared with NMR, PDF and (in situ) diffraction measurements, the materials often transforming via metastable structures. In the second example, we use in situ X-ray diffraction studies to study the high-rate cycling. Specifically, we are interested in understanding which structural classes of materials can sustain high-rate cycling - and why - and whether the mechanisms for the structural transformations that occur on lithiation/sodiation vary as a function of the rate of battery cycling. Finally, recent work to examine Ni-rich layered cathode materials will be described. These are amongst the most promising candidates for high energy density Li-ion batteries for electric vehicle applications, yet improvements in their capacity retention – particularly under conditions of stress (high/low temperature, fast charging) – are still required for their more widespread use. XRD and NMR spectroscopy are used to understand how Li-ion mobility affects the cycling behaviour of Li_xNi_0.8Co_0.15Al_0.05O₂ and NMC811 (LiNi_0.8Mn_0.1Co_0.1O₂). A long duration cell is developed to follow structural changes over multiple battery cycles and over many months.

The capabilities of 4th generation synchrotron radiation sources and X-ray free electron lasers such as high brightness, coherence and temporal structure of pulses open new horizons in the studies of structure, structural dynamics and properties of materials.

X-ray radiation coherent methods enable to get access to the 3D structure of non-crystalline samples, nanocrystals and nanostructures with a resolution theoretically limited only by the diffraction limit [1]. Such samples include, for example, various biological objects [2], biological cells, viruses and nanosized crystallites of bio macromolecules and their complexes which are difficult to crystallize.

Access to an atomic structure with ultra-high temporal resolution using ultrashort pulses of free electron lasers makes it possible to consider the different tasks of studying chemical reactions, self-organization and destruction of materials mechanisms, the formation of short-range and long-range orders, the study of phase transitions, and the complex dynamics of proteins and polymers at a fundamentally new level.

Novel scientific tasks cover a wide range of practical applications [3], including such priority areas as biotechnology and medicine, the creation of new functional materials (structural, composite, etc.), nanoelectronics and hybrid (sensors, biosensors, etc.).

Today most of the new synchrotron radiation sources have almost 100% transverse coherence, and the modernization of existing mega-facilities (for example, ESRF-EBS, PETRA IV, APS) focus on reducing the emittance (significantly less than 1 nm), increasing coherence, brightness and time resolution.

In the Russian Federation the development of coherent scattering and time resolving methods is becoming one of the priority tasks in connection with the implementation of the program for the development of the synchrotron-neutron infrastructure, including the construction of 4th generation sources: USSR-4 (synchrotron with a free electron laser) and SKIF project.

[1] J. Miao, T. Ishikawa, I. Robinson, M. Murnane Beyond crystallography: Diffractive imaging using coherent x-ray light sources. // Science. 2015. V. 348. 6234. P. 530.

[2] A. Mancuso, O. Yefanov, I. Vartanyants, Coherent diffractive imaging of biological samples at synchrotron and free electron laser facilities // Journal of Biotechnology, Volume 149, Issue 4, 2010, P. 229.

[3] H.Chapman, K. Nugent Coherent lensless X-ray imaging. // Nature Photonics. 2010. V. 4. P. 833.

Over the last few years, photon science community has been experiencing a revolution with the advent of ultra-low emittance storage rings based on Multi-Bend Achromat (MBA). In addition to green fields projects MAXIV (1), SIRIUS (2), and HEPS (3) in operation, commissioning, or construction, respectively, many third-generation facilities undertook major upgrades such as ESRF-EBS (4), APS-U (5), ALS-U (6), SLS-2 (7), DLS-2 (8), etc. All are aiming to achieve unparalleled performances in terms of average spectral brilliance, coherent flux, and nano-focusing capabilities.

After an introduction of the main concepts behind this new revolutionary concept, the new characterization techniques and their potential for new applications will be discussed, for two distinct examples, including the commissioning and operation of the ESRF-EBS (6 GeV) and the project SOLEIL (2.75 GeV) upgrade:

Since 2015 the ESRF has prepared the replacement of its old storage ring based on the double-bend achromat lattice by the EBS storage ring(9) based on the newly developed HMBA lattice with seven bending magnets per cell. During a long shutdown the EBS storage ring was installed in 2019 and went into its commissioning phase in December 2019. The EBS storage ring was successfully commissioned as the first fourth generation high energy synchrotron light source during the first six month in 2020. Nominal beam parameters could be confirmed early on in the process and the beamlines resumed user operation in September 2020 as planned. The expected improvement of the key beam parameters in terms brilliance, coherence and flux were confirmed across the entire beamline portfolio. Details on the commissioning of the beamlines and the performance reached will be presented together with early scientific results.

In 2019, SOLEIL launched a CDR (10) for an upgrade of its 20 years old storage ring with the ambition to produce round electron beams with a record low emittance of less than 50 pm.rad x 50 pm.rad, hence photon beams with an exceptional brilliance exceeding by two orders of magnitude the performances of the current source. The very broad spectral range of Soleil from THz to tens of KeV is a challenge but offers unique scientific opportunities which will be discussed and illustrated by examples in materials science and biology.

[1] Tavares, P. F., et al., “Status of the MAX-IV Accelerators”, IPAC 2019 proceedings, TUYPLM3, 1185-1190 (2019).

[2] Liu, L., “SIRIUS Commissioning Results”, IPAC 2020 (2020).

[3] Jiao Y., “The HEPS Project”, Journal of Synchrotron Radiation, 25, 1611-1618 (2018).

[4] Raimondi P., “Hybrid Multi Bend Achromat: from SuperB to EBS”, 8th International Particle Accelerator Conference, May 2017, Copenhagen, Denmark, 3670-3675,10.18429/JACoW-IPAC2017-THPPA (2017).

[5] Borland, M. et al., “The Upgrade of the Advanced Photon Source”, IPAC 2018 proceedings, THXGBD1, 2872-2877 (2018).

[6] Steier, C. et al., “Design Progress of ALS-U, the Soft X-Ray Diffraction Limited Upgrade of the Advanced Light Source, IPAC 2019 proceedings, 1639-1641 (2019).

[7] Streun, A., et al., “SLS-2: the Upgrade of the Swiss Light Source”, Journal of Synchrotron Radiation, 25, 631-641 (2018).

[8] https://www.diamond.ac.uk/Home/About/Vision/Diamond-II.html

[9] Orange Book: http://www.esrf.eu/home/orange-book.html

[10] CDR SOLEIL, https://www.synchrotron-soleil.fr, to be published

X-rays have become established as an invaluable probe for gaining an atomic insight into the structure of matter through various kinds of interaction processes, such as scattering, absorption, and emission of photoelectrons and fluorescence. Since these interactions were usually weak with the previous X-ray sources, X-ray irradiation was assumed not to modify matter. This situation has been altered by the recent advent of X-ray free-electron lasers (XFELs), which can generate brilliant femtosecond X-ray pulses.

When an XFEL pulse irradiates matter, photoelectrons and Auger electrons are emitted during or shortly after the irradiation of the pulse and trigger cascades of secondary electrons. If the radiation dose exceeds a critical value, the electron excitations strongly change interatomic potential surface and cause subsequent atomic disordering, and may even lead to the Coulomb explosion in the case of high X-ray dose. Given the time scale of electron cascading (typically, a few tens of fs) and inertia of atoms, the onset of atomic disordering is expected to take place behind the start of X-ray exposure. Indeed, it has been predicted that ultrafast X-ray pulse as short as ~10 fs with sufficient intensity can produce high-quality diffraction before the onset of substantial radiation damage, enabling structure determination of macromolecular nanocrystals and even individual biomolecule [1]. A deep understanding of transient XFEL interaction with matter is essential not only because of fundamental interest but for analyzing experiments with intense XFEL pulses.

Up to now, transient XFEL-matter interactions have been relying on theoretical modeling, validated by time-integrated measurements of charge states of ions and emitted fluorescence using a single XFEL pulse. To observe time-dependent X-ray interactions with matter, we developed a femtosecond X-ray pump-X-ray probe method [2] by combining nano-focusing optics [3] and twin XFEL pulses with controlled time separations [4] at SPring-8 Angstrom Compact free-electron LAser (SACLA) [5]. This method was applied to various materials (diamond [2,5], silicon [6], oxides, and protein crystals) and revealed the time scale of the electron excitations and the onset time of the structural changes.

In this talk, the XFEL-induced transient structural changes in matter revealed by the pump-probe experiments are discussed. In addition, preliminary results of the advanced pump-probe experiments using seeded-XFEL pulses [7,8] will be presented.

[1] Neutze, R., Wouts, R., Van der Spoel, D., Weckert, E., Hajdu, J. (2000). Nature 406, 752.[2] Inoue, I., Inubushi, Y., Sato, Y., Tono, K., Katayama, T., Kameshima, T., Ogawa, K., Togashi, T., Owada, S., Amemiya, Y., Tanaka, T., Hara, T., & Makina, Y. (2016). Proc. Natl. Acad. Sci. USA 113, 1492.[3] Mimura, H., Yumoto, H., Matsuyama, S., Koyama, T., Tono, K. et al., (2014). Nature Commun. 5, 3539.[4] Hara, T., Inubushi, Y., Katayama, T., Sato, T., Tanaka, H., Tanaka, T., Togashi, T., Togawa, T., Tono, K., Yabashi, M. & Ishikawa, T. (2014). Nat. Commun. 4, 2919.[5] Inoue, I., Deguchi, Y., Ziaja, B., Osaka, T., Abdullah, M. M., Jurek, Z., Medvedev, N., Tkachenko, V., Inubushi, Y., Kasai, H., Tamasaku, K., Hara. T., Nishibori, E. & Makina, Y. (2021). Phys. Rev. Lett. 126, 117403.[6] Hartley, N., Grenzer, L., Huang, L., Inubushi, Y., Kamimura, N., Katagiri, K. et al. (2021). Phys. Rev. Lett. 126, 015703.[7] Inoue, I., Osaka, T., Hara, T., Tanaka, T., Inagaki, T. et al. (2019). Nature Photon. 13, 319.[8] Inoue, I., Osaka, T., Hara, T. & Yabashi, M. (2020). J. Synchrotron Rad. 27, 1720.

Serial femtosecond crystallography (SFX) at X-ray free-electron lasers (XFELs) enables essentially radiation damage-free macromolecular structure determination using microcrystals that are too small for synchrotron studies [1]. However, SFX experiments often require large amounts of sample in order to collect highly redundant data where some of the many stochastic errors can be averaged out and accurate structure factor amplitudes determined [2]. Recently, an improvement in native-SAD phasing of SFX data was demonstrated by utilizing longer wavelengths that increased the strength of the anomalous signal [3]. This reduced up to 10-fold the number of indexed images needed for successful de novo structure determination. Another approach to reduce the number of indexed images, applicable not only to de novo phasing but also to molecular replacement strategies, is to use polychromatic (pink) X-ray pulses for SFX. Theoretically, faster convergence rates of the Monte Carlo approach can be achieved by increasing the bandwidth or divergence of the X-ray pulses [4, 5].

We used the capability of the Swiss free-electron laser (SwissFEL) to generate large-bandwidth X-ray pulses (Δλ/λ = 2.2 % FWHM) and applied them in SFX with the aim of improving the partiality of Bragg spots and thus decreasing sample consumption while maintaining the data quality. Sensitive data-quality indicators such as anomalous signal from native thaumatin micro-crystals and de novo phasing results were used to quantify the benefits of using pink X-ray pulses to obtain accurate structure factor amplitudes. Compared to data measured using the same setup but X-ray pulses with typical, quasi-monochromatic XFEL bandwidth (Δλ/λ = 0.17 % FWHM), up to four fold reduction in the number of indexed diffraction patterns required to obtain similar data quality was achieved. This novel approach, pink-beam SFX, facilitates the yet underutilized de novo structure determination of challenging proteins at XFELs, thereby opening the door to more scientific break-troughs.

[1] Nass, K. (2019). Acta Cryst. D 75, 211-218.

[2] Nass, K., Meinhart, A., Barends, T. R., Foucar, L., Gorel, A., Aquila, A., Botha, S., Doak, R. B., Koglin, J., Liang, M., Shoeman, R. L., Williams, G., Boutet, S. & Schlichting, I. (2016). IUCrJ 3, 180-191.

[3] Nass, K., Cheng, R., Vera, L., Mozzanica, A., Redford, S., Ozerov, D., Basu, S., James, D., Knopp, G., Cirelli, C., Martiel, I., Casadei, C., Weinert, T., Nogly, P., Skopintsev, P., Usov, I., Leonarski, F., Geng, T., Rappas, M., Doré, A. S., Cooke, R., Nasrollahi Shirazi, S., Dworkowski, F., Sharpe, M., Olieric, N., Bacellar, C., Bohinc, R., Steinmetz, M. O., Schertler, G., Abela, R., Patthey, L., Schmitt, B., Hennig, M., Standfuss, J., Wang, M. & Milne, C. J. (2020). IUCrJ 7, 965-975.

[4] Dejoie, C., McCusker, L. B., Baerlocher, C., Abela, R., Patterson, B. D., Kunz, M. & Tamura, N. (2013). J. Appl. Cryst. 46, 791-794.

[5] White, T. A., Barty, A., Stellato, F., Holton, J. M., Kirian, R. A., Zatsepin, N. A. & Chapman, H. N. (2013). Acta Cryst. D 69, 1231-1240.

Keywords: Pink-beam; serial femtosecond crystallography; de novo protein structure determination; X-ray crystallography; SFX; SAD; single-wavelength anomalous diffraction; XFEL; large-bandwidth

The three probes of the structure of matter in biology (X-rays, neutrons and electrons) have complementary properties and strengths. The balance between these three structural research probes, within their strengths and weaknesses, is perceived to change, even dramatically so at times. Of course for understanding biological systems the required perspectives are:- physiologically relevant temperatures and relevant chemical conditions. These remain very tough challenges because e.g. cryoEM looks never to set foot in room temperature and crystallization often requires non-physiological chemical conditions. X-ray crystallography especially from the synchrotron has brought huge improvements in analytical capability and dominates the PDB. CryoEM has also brought great advantage for structural studies of non-crystallisable complexes. Overall, integrated structural biology techniques and functional assays make a package towards physiological relevance of any given study. X-ray laser serial fsec crystallography experiments aimed at structural dynamics and neutron macromolecular crystallography aimed at determining protonation states of ionisable amino acids are both, as a spin off, yielding room temperature structures, as well as being damage free. Comparisons between room and cryo biological structures are increasing as the X-ray laser and neutron facilities expand in number and grow in capability; structural differences are being increasingly described in many papers. We need to expand these facility provisions for room temperature studies. Likewise the extremely bright sources such as ESRF2 ie "EBS" will bring a larger number of room temperature results through the serial crystallography approach but with X-ray radiation damage effects yet to be quantified.

Dynamical diffraction effects, also known as echoes, produced in thin crystals in both forward and diffracted directions are of highest importance for X-ray optics at ultrafast sources, as XFELs, and for the study of ultrafast phenomena in micron-sized single crystals. These echoes present delays of few fs between each other and the transmitted beam (similar as it happens with sound echoes, but in this case of electromagnetic nature and therefore with the speed of light). The delay relates to a displacement of the monochromatic diffracted beams in the transverse direction to the X-ray beam propagation [1,2]. Such echoes are used in self-seeding forward monochromators at hard xFELs.

We would like to present our work performed at NanoMAX, MAX IV laboratory, Sweden, in which we image the dynamical diffraction wavefront from a 100 um thick Si wafer [3]. The work uses the full coherence and high flux of NanoMAX, together with the technique known as tele-ptychography [4], to image the forward diffracted wavefront at a pinhole located 3 mm downstream the sample. As presented in figure 1, the data collected is reconstructed using a ptychography algorithm in the pinhole plane, obtaining amplitude and phase of the wavefront. The wavefront is propagated back to the focus where, combined to the small size of the X-ray beam provided by NanoMAX, provides a high- resolution (55 nm) image for the detection of forward diffracted echoes.

The work underline how this effect must be taken into account in the imaging and study of samples with thickness of the order of the X-ray extinction length. We also show that a strain induced in the surface can modulate the temporal delay of the dynamical diffraction waves as presented in the second figure attached. All the work is accompanied with the simulation of the effect using a self-written code, that can be used to model both temporal and static strains in single crystal samples, as well as in micro-pillars in which these dynamical effects are also present [5].

[1] A. Rodriguez-Fernandez et al., ActaCryst. A74, 75 (2018);

[ 2] Y. Shvydko and R. Lindberg, Phys. Rev. ST Accel.Beams15, 100702 (2012);

[3] A. Rodriguez-Fernandez et al., "Imaging ultrafast dynamical diffraction wavefronts in strained Si with coherent X-rays" arXiv:2012.08893 (2020)

[4] E. H. R. Tsai et al, Optics Express 34 (2016) 6441;

[5] M. Verezhak et al. "X-ray ptychographic topography, a new tool for strain imaging" PRB (2021);

Hybrid photon counting (HPC) X-ray detectors are crucial ingredients for cutting-edge synchrotron research [1] by providing noise-free detection with advanced acquisition modes. In this regard, the latest HPC detector generation EIGER2 is setting new performance standards that push current horizons in X-ray science. These detectors combine all advantages of previous HPC detector generations while offering (i) 75 µm × 75 µm pixel size, (ii) kilohertz frame rates, (iii) negligible dead time (100 ns) and (iv) count rates of 10⁷ photons per pixel.

Recently, EIGER2 detectors are available both with silicon and with CdTe sensors to provide high quantum efficiency at energies up to 100 keV. Two separately adjustable energy thresholds allow for reduction of high-energy background such as from cosmic radiation or higher harmonics radiation. For one, this active background suppression significantly improves signal-to-noise in laboratory applications where weaker signals are expected. For the other, these benefits advance established methods like crystallography and small angle X-ray scattering and empower new fields of research, such as X-ray photon correlation spectroscopy and coherent studies.

Here, we present results from detector characterization and application experiments, highlighting key properties such as count rate capability, readout and spatial resolution. We will further show the potential capabilities of newly released detector features, such as the double-gating acquisition mode for shot-to-shot background correction. Combined with characterization measurements at beamlines and in the laboratory, these results evidence how the EIGER2 detector systems will advance static and time-resolved X-ray experiments.

[1] Förster, A., et al. (2019) Philos. Trans. R. Soc. Math. Phys. Eng. Sci. 377, 20180241.

Of the over 6,000 confirmed and candidate extrasolar planets discovered to date, those 1-4 times the radius of the Earth are found to be most abundant. MgO (periclase), is expected to be a major component of the deep mantles of terrestrial planets and exoplanets. Its high-pressure transformation from a rocksalt (B1) structure to the B2 (CsCl) structure is expected to occur in rocky exoplanets greater than about 5 Earth masses in size. In this work, the structure and temperature of MgO upon shock compression over the 200-700 GPa pressure range was examined at the Omega-EP Laser facility. Laser drives of up to 2 kJ over 10 ns were used to shock compress single-crystal MgO. At peak compression, the sample was probed with He-α X-rays from a laser-plasma source. Diffracted X-rays were recorded on image plates lining the inner walls of a box attached to the target package. For each shot we measure pressure (velocity interferometry), density (x-ray diffraction) and shock temperature (pyrometry). We also probe orientation-dependence of the shock Hugoniot by conducting laser-driven decaying shock measurements of single crystal MgO [100], [111] and [110], and will discuss the importance of single crystal experiments to better improve phase diagram models of materials at extreme conditions.

Fast compression in the dynamic diamond anvil cell (dDAC) allows for the study of materials at intermediate strain rates that are not accessible using traditional static and dynamic compression techniques [1]. Previous dDAC studies revealed compression-rate dependent phenomena such as rate-dependent phase transformation pathways [2], the formation of metastable phases [3], and shifts in phase transition boundaries from their equilibrium positions [2,3,4]. The fast diffraction set-up at the Extreme Conditions Beamline (P02.2) at PETRA-III offers time-resolved X-ray diffraction with kHz data collection rates, which allows for phase transition boundaries to be accurately determined at compression rates up to ~1000 GPa/s. Future experiments at the European XFEL will allow for data collection rates up to 4.5 MHz, which will extend these studies to compression rates >100 TPa/s.

In order to develop a full understanding of phase transitions under dynamic compression, it is necessary to investigate sample behaviour on both atomistic (crystal structure) and microscopic (crystal morphology) length scales. This allows for kinetic parameters such as nucleation and growth rates to be determined. When crystallite of the high pressure phase have well-defined phase boundaries, imaging techniques can be used to visualize the growth of the new phase. The X-ray phase contrast imaging platform at P02.2 allows for the visualization of samples that are opaque to visible light, where the simultaneous X-ray diffraction measurements allow for pressure determination, phase identification, and structural refinement. Phase contrast imaging allows us to resolve phase boundaries for grains of similar Z, where conventional absorption-based imaging typically fails.

Here, we present results from X-ray imaging experiments on dynamically-compressed Ga (Fig. 1), where we have successfully imaged pressure-induced melting (Ga-I/liquid) and solidification (liquid/Ga-III). Using an imaging configuration in which the sample is positioned upstream from the focal spot of a CRL-focussed X-ray beam allows for the collection of ‘clean’ diffraction patterns with minimal contribution from the gasket material, and produces clearly-defined solid/liquid phase boundaries in the X-ray images.

[1] Jenei, Zs. et al. Rev. Sci. Instrum. 90, 065114 (2019). [2] Lee, G. W., Evans, W. J. & Yoo, C. S. Phys. Rev. B 74, 134112 (2006). [3] Chen, J. Y & Yoo, C. S. PNAS 108 7685-7688 (2011). [4] Husband. R. J. et al. ‘Compression-rate dependence of pressure-induced phase transitions in Bi’, submitted.

Extreme conditions are ubiquitous in nature. Much of the matter in the universe exists under high pressures and temperatures. Of interest, are the planetary interiors of the icy giants, Uranus and Neptune. Which have particularly complex magnetic fields [1].

To understand these complex magnetic fields the conditions and composition of icy giant planetary interiors need to be determined. The interiors of these planets are understood to contain mixtures of water, ammonia and hydrocarbons [2].

Under compression the phase diagram of ice is rather complex. With several phases determined and predicted under high pressure and temperature conditions [3]. High pressure ice above ~1500K and 50 GPa is predicted to undergo a superionic transition, where the hydrogen atoms diffuse into the oxygen sub- lattice [4,5]. These superionic phases are a possible source of the complex magnetic fields of both Uranus and Neptune.

Several high-pressure phases of water have been observed in the superionic region of the phase diagram. A body-centred cubic (bcc) phase, which if superionic would be analogous to ice X structure and with increasing pressure a phase transition to a face centred cubic (fcc) phase has been reported [5].

Experiments carried out at the MEC end station at the LCLS XFEL in December 2020, utilised reverberating shocks to compress water into Off-Hugoniot states within the superionic region of the ice phase diagram [6]. Liquid water samples were confined between a diamond ablator and a rear window, reaching P-T states ranging from ~40 GPa and 1200K to ~200 GPa and 4000K.

The bcc phase of ice has been observed from ~50 GPa and ~1200 K. A mixed phase region starting at ~90 GPa and ~2500 K, has been of observed with the bcc phase and a second phase. With increasing pressure the second phase becomes more prominent with the loss of the initial bcc phase.

The higher-pressure ice initially appears to be the fcc phase as described by Millot et al. However, further examination of the diffraction revealed misfits to the fcc lattice and a lack of refinement has suggested that that this may in fact be a different structure. The structure of this phase has yet to be determined. However, several candidates are proposed from predicted high pressure ices [7].

Ongoing work aims to determine these structures of ice under superionic P-T conditions and with comparison with simulation, understand the magnetic field behaviour of icy giant type planets.

Acknowledgements: The work was supported by the Helmholtz Association under VH-NG- 1141 and ERC-RA-0041. Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. The MEC instrument is supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences under Contract No. SF00515.

[1] W.J. Nellis, J. Phys.: Conf. Ser. 950, 042046 (2017)

[2] M. D. Hofstadter et al., Ice Giants: Pre- Decadal Survey Mission Study Report, NASA-JPL report JPL-D-100520 (2017)

[3] C. G. Salzmann, J. Chem. Phys 150, 06091 (2019)
[4] I. A. Ryzhkin, Sol. Stat. Com. 56, 1 (1985)

[5] M. Millot et al., Nat. 569, 7755 (2019)

[6] M. Millot et al., Nat. Phys. 14, 3 (2018)

[7] A. Hermann et al., PNAS 109, 3 (2012)

Au has long been regarded as an important calibration standard in the high-pressure diffraction community, especially for experiments involving diamond anvil cells. The face centred cubic phase of Au is believe to be stable for hundreds of GPa at room temperature [1,2]. Recent dynamic-compression work has shown that the high-pressure behaviour of Au is not as simple at higher temperatures, and under laser-driven shock-compression, Au was found to transform, on-Hugoniot, from its ambient face centred cubic phase to a body centred cubic phase at 223 GPa before melting around 320 GPa [3].

As well as being used as a calibration standard, Au is also a commonly used material in target packages for laser-driven, dynamic-compression experiments. For experiments that explore the behaviour of various materials at the highest pressures and temperatures achievable (such as the experiments conducted at the National Ignition Facility or at the Omega laser facility) a layer of Au may be placed before the material of interest to act as a shield to prevent x-ray heating of the material of interest before the compression wave has reached the sample. For many of these experiments, the compression wave is not necessarily a shock wave, but the target may instead be ramp-compressed meaning that the compression state does not lie on the Hugoniot.

Given the frequent use of Au in diffraction experiments at extreme conditions, it is important that its high-pressure, high-temperature behaviour is well constrained off-Hugoniot so that we may correctly identify its contribution to diffraction data collected in this regime. To this end, a series of shock and ramp compression experiments have been conducted across various laser-compression platforms to explore the extent of the high-pressure bcc phase of Au. These experiments involve the compression of Au to previously unexplored pressures and temperatures, utilizing diffraction and velocity interferometry as the primary diagnostics. This talk presents a discussion of these results and reconciles this new, unpublished data with existing findings within the field.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

[1] Dubrovinsky, L., Dubrovinskaia, N., et al. (2007). Phys. Rev. Lett. 98, 045503
[2] Boettger, J.C. (2003) Phys. Rev. B. 67, 174107
[3] Briggs, R.J., et al., (2019) Phys. Rev. Lett. 123, 045701

Non-hydrostatic stress is known to change the evolution of unit cell parameters [1] and the compression of bond lengths and angles in the structures of crystals, e.g. [2]. The resulting modifications in the structures can lead to changes in the physical and thermodynamic properties of crystals, and thus change their thermodynamic stability. As a consequence, both reconstructive phase transitions [3] and displacive-type symmetry-breaking phase transitions [4] under deviatoric stress can occur at different temperatures and different mean stress than under hydrostatic pressure. Despite its importance, the effect of non-hydrostatic stress on crystal structures is still poorly understood, because it is challenging to perform experiments under controlled deviatoric stress conditions. On the other hand, mineral host-inclusion systems composed of a mineral entrapped inside another mineral provide the perfect example to characterize a crystal under deviatoric stress. Because the inclusion is entrapped inside another crystal, it will not be under hydrostatic pressure and the deviatoric stress imposed on it will be the result of the difference in the elastic properties of the two crystals and their mutual crystallographic orientations. In this contribution, we describe a methodology to characterize the effect of deviatoric stress on inclusion crystal structures using synchrotron x-ray diffraction, including how to deal with the experimental challenges in the collection of intensity data from a host-inclusion system, and the evaluation of the quality of the results. The quartz in garnet system is an ideal candidate for this study. Quartz has a simple and well-known structure, whose variation with pressure and temperature has been widely characterised, while garnet, being cubic, imposes an almost isotropic strain on the inclusions, thus providing a relatively simple case study. Furthermore, quartz is one of the most common mineral inclusions in different types of rocks, so it qualifies as an interesting case for geological applications.

[1] Bassett, W. A. (2006). J. Phys.: Condens-Mat., 18(25), S921.
[2] Gatta, G. D., Kantor, I., Ballaran, T. B., Dubrovinsky, L., & McCammon, C. (2007). Effect of non-hydrostatic conditions on the elastic behaviour of magnetite: an in situ single-crystal X-ray diffraction study. Phys, Chem. Miner., 34(9), 627-635.
[3] Richter B., Stünitz H. & Heilbronner R. (2016) J. Geophys. Res. -Solid Earth, 121, 8015-8033.
[4] Bismayer U., Salje E. & Joffrin C. (1982) J. Phys., 43, 1379-1388.

The strong interest in MOCl (M = Ti, V, Cr, Fe) compounds stems from their nonlinear optical properties in the IR band (CrOCl) [1], their use as intercalation compounds for cathode materials (FeOCl) [2], their use as parent structures for van der Waals heterostructures [3] and especially from their low-dimensional magnetic phenomena [4-6].

MOCl-type compounds are isostructural at ambient conditions with the space group Pmmn and consist of double layers of distorted MO₄Cl₂ octahedra, which are connected by van der Waals forces. It has been shown that the magnetic behaviour and the dimensionality of MOCl-type compounds is determined by orbital order of the 3d electron of the transition metal [4-6]. For M = V, Cr, Fe orbital order leads to strong intra- and interchain exchange couplings, which results in quasi-two-dimensional (2D) magnetic systems that exhibit antiferromagnetic (AFM) order at low temperatures [4,5]. The transition to the AFM state is characterized by a magneto-elastic coupling in the form of a monoclinic lattice distortion that lifts the geometric frustration of the magnetic order on the orthorhombic crystal structure as well as by the formation of an incommensurate modulation of the structure [4,5].

Applying hydrostatic pressure to those compounds allows us to continuously adjust the intra- and interchain exchange parameters through the modification of the octahedral geometry and the metal-to-metal distances. This provides a unique opportunity to study the interplay between magnetic order and pressure-induced structural changes in dependence of the electronic configuration of the transition metal within one single structure type. Pressurizing MOCl compounds to approximately 15 GPa leads to a normal-to-incommensurate phase transition, characterized by an optimization of the interlayer packing, which is not associated with changes in the electronic or magnetic structure [7]. This gives us, in addition, the possibility to investigate the effect of the high-pressure structural transition on the magnetic order and vice versa.

The high-pressure (HP) low-temperature (LT) single crystal X-ray diffraction experiments, which were conducted at P02.2/PETRA III above and below T_N,1bar for pressures up to 40 GPa and temperatures down to 6 K, provides an insight into the HP-LT mechanisms of FeOCl: The magneto-elastic coupling is governed by a monoclinic lattice distortion below T_N,1bar, whereas an interplay between lattice distortion and significant structural changes takes place above T_N,1bar. These changes enhance, from a geometrical perspective, superexchange interactions up to a pressure of ≈ 15 GPa where the structural HP phase transition gets superimposed on the further structural development. We will present the sequence of phase transitions and the structural development of FeOCl in detail and compare it, where applicable, with the quasi-2D compound CrOCl.

With the described approach and an in-depth analysis of structural changes, we aim at disentangling the magneto-structural correlations in the model system of MOCl as a function of composition, temperature and pressure in order to facilitate the understanding of low-dimensional magnetic systems in general.

This work summarizes developments attained in oral vaccine formulations based on the encapsulation of antigens inside porous silica matrices. These vaccine vehicles protect the proteins from the harsh acidic stomach medium, allowing them to reach the Peyer´s patches, inducing immunity. Focusing on the pioneer research conducted at Butantan Institute, in Brazil, the results report the optimization of the antigens´ encapsulation yield, as well as their homogeneous distribution inside the meso and macro porous network. The characterization plus modelling of pure antigens having different dimensions and their complexes, like silica with hepatitis B virus like particles and diphtheria anatoxin, were performed by Small Angle X-ray Scattering (SAXS), X-ray Absorption Spectroscopy (XAS), X-ray Phase Contrast Tomography (XPCT) and neutron and X-ray imaging. The association of these techniques with complementary ones provided a clear picture of the proposed vaccines. Mice with variable high and low humoral responses presented significant levels of antibodies, proving the efficacy of the proposed oral immunogenic complex.

Over the past 40 years, the use of group representation theory has transformed the study of phase transitions in crystalline materials. From my own perspective, I will present the history and development of the innovative methods and computational infrastructure that have supported this transformation. Highlights will include (1) the tabulation of irreducible representations for crystallographic space groups and their superspace extensions, (2) the determination of isotropy subgroups, (3) the projection and parameterization of symmetry modes, (4) the tabulation of superspace symmetry groups, (5) and the development of the online ISOTROPY Software Suite, which makes all of these advances and data sources immediately and freely accessible to the international research community.

Organic crystal structures, solved and refined from powder data, may be fully wrong, even if they are chemically sensible and give a good fit to the powder patterns.

Two examples are shown.

In both cases, the atomic positions and the molecular packing were completely wrong.

Example 1:

The crystal structure of the commercial organic hydrazone Pigment Red 52:1, Ca²⁺(C₁₈H₁₁ClN₂O₆S)^2-*H₂O was determined from powder data in the usual way by indexing, structure solution by real-space methods, and Rietveld refinement. The resulting structure was chemically sensible and gave a good fit to the powder data. By chance, a single-crystal of poor quality was obtained, and the correct structure was determined by a combination of single-crystal structure analysis and Rietveld refinement. The structure initially determined from powder data turned out to be completely wrong. The correct and the wrong structures differ in the position and coordination of the Ca²⁺ ions, as well as the position and mutual arrangement of the anions (see Figure).

Example 2:

The crystal structure of 4,11-difluoroquinacridone, C₂₀H₁₀F₂N₂O₂, was solved from unindexed powder data by a global fit of millions of random structures to the powder pattern using the FIDEL method [1,2], which uses cross-correlation functions for the comparison of experimental and simulated powder patterns. The structures were subsequently refined by the Rietveld method. Four completely different structures (different space groups, different molecular packings, different H bond topolgies) were obtained. All four structures were chemically sensible, had a good fit to the powder data, gave a good fit to the pair-distribution function and good lattice energies. One is correct, the other were wrong [3].

[1] S. Habermehl, P. Mörschel, P. Eisenbrandt, S.M. Hammer, M.U. Schmidt, Acta Cryst. B70 (2014), 347-359.

[2] S. Habermehl, C. Schlesinger, M.U. Schmidt, in preparation.

[3] C. Schlesinger, A. Fitterer, C. Buchsbaum, S. Habermehl, M.U. Schmidt, in preparation.

Next generation materials of nearly every kind rely on chemical, electronic, and/or magnetic heterogeneity for creating, harnessing, and controlling functionality. Exploration of these phenomena increasingly involve multiple length-scale scattering probes and require sophisticated modeling approaches to characterize and understand them. Total scattering methods, including both Bragg and diffuse scattering signals, are providing key insights into how long-range, nanoscale, and local atomic structure motifs differ in materials and cooperate to deliver their unique properties. The nuances of capturing nanoscale heterogeneities, including correlated defects, chemical short-range order, and stacking fault distributions, represent a modern frontier in the field of crystallography. We will explore this theme through detailed investigation of two distinct materials classes. First, we will present the operando study of nanostructured fluorite catalysts. We will specifically follow the nature of correlated oxygen vacancies at elevated temperatures, including their behavior under acid-gas exposure. Second, we will present structure-property characteristics of new pyrochlore and perovskite high entropy oxides (HEOs). HEOs exhibit a single-phase crystal structure containing five or more different metal cations of the same amount on single crystallographic lattice sites; their compositional and configurational disorder and associated structural diversity offer great potential for unique material characteristics. We will highlight contemporary challenges and opportunities in the quest to extract crystal structure models from experimental data with the detail needed to guide and validate solid state theories, and design new and improved functional materials.

Most of the natural or fabricated fibrous materials exhibit multiscale structures, which critically influence their mechanical, optical, and electronic properties. Therefore, knowing the structure is important to steer the properties or design novel fibrous material. This requires multiscale structural characterization to enrich their structure-properties relationship. State-of-the-art small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques are extremely powerful to characterize such materials from the nanometer to the Ångström scale [1].

In this contribution, multiscale structural insights of different fibrous materials such as electrospun nanofiber scaffolds [1], thermal protective fabrics [2], and fibrous biocomposite tissues would be presented with emphasis on their structure-properties relationship primarily using SAXS and WAXD methods. The schematic of the multiscale structure of the electrospun nanofiber scaffolds is shown in figure 1 as an example. Furthermore, the application of gained structural knowledge to steer the properties of polymeric nanofibers and the design of novel humid responsive nanofibrous scaffolds would be discussed.

[1] A.K. Maurya, L. Weidenbacher, F. Spano, G. Fortunato, R.M. Rossi, M. Frenz, A. Dommann, A. Neels, A. Sadeghpour, Structural insights into semicrystalline states of electrospun nanofibers: a multiscale analytical approach, Nanoscale 11(15) (2019) 7176-7187.

[2] A.K. Maurya, S. Mandal, D.E. Wheeldon, J. Schoeller, M. Schmid, S. Annaheim, M. Camenzind, G. Fortunato, A. Dommann, A. Neels, A. Sadeghpour, R.M. Rossi, Effect of radiant heat exposure on structure and mechanical properties of thermal protective fabrics, Polymer 222 (2021) 123634.

Orientation and conformation in nanoscale amorphous regions often dominate the properties of soft materials such as composites and semicrystalline polymers. Robust correlations between between structure in these amorphous regions and important properties are not well developed due to a lack of measurements with high spatial resolution and a sensitivity to molecular orientation. I will describe our approach to solving this issue using polarized resonant soft X-ray scattering (P-RSoXS), which combines principles of soft X-ray spectroscopy, small-angle scattering, real-space imaging, and molecular simulation to produce a molecular scale structure measurement for soft materials and complex fluids.

Because P-RSoXS is relatively new to the scattering community, I will first cover the basics of the measurement. The fundamental principles of P-RSoXS and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, the spectroscopic basis for P-RSoXS, will be reviewed. The P-RSoXS experiment will be discussed including sample preparation and constraints, which differ considerably from analogous scattering techniques such as conventional small-angle X-ray scattering (SAXS) and small angle neutron scattering (SANS). I will also cover approaches for including gases or liquids in the experiment, and describe available measurement facilities. Data collection best practices will be reviewed.

I will then describe polarized resonant soft X-ray scattering (P-RSoXS) measurements of model systems including polymer-grafted nanoparticles. Analysis will focus on quantitative extraction of orientation details from nanoscale glassy regions. This work is now accelerated by a powerful analysis framework using parallel computation across graphics processing units (GPUs) for the forward-simulation of P-RSoXS patterns. In polymer-grafted nanoparticles, we can apply this framework to fit quantitative and detailed descriptions of amorphous chain orientation with ≈ 2 nm resolution.

Characterising the supramolecular organisation of macromolecules in the presence of varying degrees of disorder remains one of the challenges of structural research. Discotic liquid crystals (DLCs) are an ideal model system for understanding the role of disorder on multiple length scales. Consisting of rigid aromatic cores with flexible alkyl fringes, they can be considered as one-dimensional fluids along the stacking direction and they have attracted attention as molecular wires in organic electronic components and photovoltaic devices [1].

With its roots in single-particle imaging, fluctuation x-ray scattering (FXS) [2] is a method that breaks free of the requirement for periodic order. However, the interpretation of FXS data has been limited by difficulties in analysing intensity correlations in reciprocal space [3]. Recent work has shown that these correlations can be translated into a three-and four-body distribution in real space called the pair-angle distribution function (PADF) – an extension of the familiar pair distribution function into a three-dimensional volume [4]. The analytical power of this technique has already been demonstrated in studies of disordered porous carbons and self-assembled lipid phases [5,6].

Here we report on the investigation of order-disorder transitions in liquid crystal materials utilising the PADF technique and the development of facilities for FXS measurements at the Australian Synchrotron

X-Ray Free Electron Lasers provide a means of conducting crystallography experiments with remarkable time and spatial resolution. These methods can directly recover the electron density of materials. However, there are stringent requirements such as crystal size, number density per exposure, and the crystal order which are required for reconstruction. Membrane proteins, which do not readily crystallise or meet these requirements [1], are particularly interesting to study as they comprise up to 50% of drug targets [2], but less than 10% of the protein structures in the Protein Data Bank [3].

The Pair Angle Distribution Function (PADF) describes the three and four body correlations of the electron density in a sample, and can be recovered from X-ray cross-correlation analysis (XCCA) [4]. Although PADF analysis does not recover the electron density directly, it still contains significant information about the local three dimensional structure of the material. PADF analysis also has the potential to relax the stringent crystal requirements of current single crystal experiments.

We discuss the sensitivity of the PADF to different protein structures [5], and the correlations generated at different length scales; from atomic bonding to tertiary structure. Our aim is to further develop PADF analysis to recover crystal structure factors using X-ray cross-correlation analysis.

[1] Johansson, L.C.; Arnlund, D.; White, T.A.; Katona, G.; DePonte, D.P.; Weierstall, U.; Doak, R.B.; 
Shoeman, R.L.; Lomb, L.; Malmerberg, E.; et al. Lipidic phase membrane protein serial femtosecond 
crystallography. Nat. Methods 2012, 9, 263–265.

[2] Cournia, Z.; Allen, T.W.; Andricioaei, I.; Antonny, B.; Baum, D.; Brannigan, G.; Buchete, N.V.; Deckman, J.T.; Delemotte, L.; del Val, C.; et al. Membrane protein structure, function, and dynamics: A perspective from experiments and theory. J. Membr. Biol. 2015, 248, 611–640.


[3] Berman, H.M.; Battistuz, T.; Bhat, T.N.; Bluhm, W.F.; Bourne, P.E.; Burkhardt, K.; Feng, Z.; Gilliland, G.L.; Iype, L.; Jain, S.; et al. The Protein Data Bank. Acta Crystallogr. Sect. D Biol. Crystallogr. 2002, 58, 899–907.

[4] Martin, A.V. Orientational order of liquids and glasses via fluctuation diffraction. IUCrJ 2017, 4, 24–36.

[5] Adams, Patrick, et al. "The Sensitivity of the Pair-Angle Distribution Function to Protein Structure." Crystals 10.9 (2020): 724.


A painting is made up of complex mixtures of materials, carefully selected by an artist, usually to create a specific optical illusion or esthetic effect. Depending on its material composition and the environmental conditions that a painting is subjected to, various chemical reactions can take place which cause the paint layers to deteriorate over time. Therefore, collecting reliable chemical information from a work of art is essential to understand its composition, past and ongoing conservation issues and to develop preservation strategies. In this sense, X-ray powder diffraction is an important tool as it allows for the direct identification of crystalline phases within the complex mixtures present in a painting [1]. However, an important limitation of this method has been the amount of material that needed to be sampled [2]. In the past decade a new trend has been set towards the application of elemental and chemical imaging techniques, such as macroscopic X-ray fluorescence (MA-XRF) and reflectance imaging spectroscopy (RIS), for the study of painted artefacts as they provide valuable information on the heterogeneous composition within complete paintings [3-5].

Following this trend, the AXES research group has developed a macroscopic X-ray powder diffraction (MA-XRPD) imaging instrument that allows for the identification and visualization of the crystalline materials used in a painting in a non-invasive manner. This instrument uses a low power microfocus X-ray source (IµS, Incoatec) combined with multilayer mirrors to obtain a slightly focused and fairly monochromatic X-ray beam in combination with a large area detector (PILATUS 200K, Dectris). By moving the painting and the instrument relative to each other, a large set of diffraction images (typically >10000) is collected following a raster-scanning approach. Subsequently, this large powder diffraction dataset is azimuthally integrated after which the resulting one dimensional 2θ spectrum at each data point is individually fitted with the XRDUA software package [6] using a model comprising all identified crystalline phases. By plotting the scaling factors as grey-scale values individual images that correspond to the distribution of the crystalline materials can be created [7].

The MA-XRPD instrument can be used in a transmission geometry, suitable for underlaying and strongly absorbing paint layers, or in reflection geometry, which is more sensitive for the (thin) pictorial layers. The latter also has the added advantage that larger works of art can be investigated as the painting remains stationary while the scanning head is translated in three dimensions. Typically a (short) dwell time of 10 seconds is used with a step size of 1-2 mm over a maximum scanning range of 30 x 30 cm.

The MA-XRPD instrument has been used within several museums on well-known masterpieces, such as Van Gogh’s Sunflowers, Vermeer’s Girl with a Pearl Earring, the Ghent altarpiece by the brothers Van Eyck and The Night Watch by Rembrandt. On these works, next to the visualization of the original pigments employed by the artists and later additions or overpaint, also various chemical alteration products that have formed within/on top of the paint layers could be identified. In some cases, the data collected with the MA-XRPD instrument can be exploited to yield other types of highly-specific information, such as the buildup of the paint layer or the orientation of the crystals on the paint surface. Furthermore, the collection of large datasets allows a reliable quantification of various pigment mixtures and to track their differences within and between artworks/time periods.

[1] Artioli, G. (2013). Rendiconti Lincei-Scienze Fisiche E Naturali, 24, S55. [2] Madariaga, J. M. (2015). Anal. Methods, 7, 4848. [3] Alfeld, M., & Broekaert, J. A. C. (2013). Spectrochim. Acta, Part B, 88, 211. [4] Alfeld, M., & de Viguerie, L. (2017). Spectrochim. Acta, Part B, 136, 81. [5] Trentelman, K. (2017). Annu. Rev. Anal. Chem., 10, 247. [6] De Nolf, W., Vanmeert, F., & Janssens, K. (2014). J. Appl. Crystallogr., 47, 1107. [7] Vanmeert, F., De Nolf, W., De Meyer, S., Dik, J., & Janssens, K. (2018). Anal Chem, 90, 6436.

High-strength lightweight magnesium (Mg) alloys have substantial potential for reducing the weight of automobiles and other transportation systems and, thus, for improving fuel economy and reducing emissions. However, compared to other structural metals, the development of commercial Mg alloys and our understanding of Mg alloy physical metallurgy are less mature, and enabling the widespread use of Mg alloys requires significant improvement in strength, fatigue, and formability. The low formability of Mg alloy sheet is due to its strong basal texture in the rolling direction. The addition of Ca and rare earth elements can result in a desired weaker texture. However, despite numerous studies, the mechanisms by which this texture reduction occurs remains unknown, and it is likely that several different mechanisms occur simultaneously or sequentially. This is the topic of this research.

A Mg-3Zn-0.1Ca alloy was deformed under hot plane-strain compression and samples were subjected to annealing on ID3A on ID3A at the Cornell High Energy Syncrhotron Source (CHESS) and ID06 at the European Synchrotron Radiation Facility (ESRF). In-situ far-field and near-field high-energy diffraction microscopy (ff- and nf-HEDM) characterization was performed at CHESS, and in-situ partial intermediate-field HEDM (if-HEDM) and dark-field X-ray microscopy (DFXM) was performed on ID06 at the ESRF. By combining the different modalities, we were able to characterize the microstructure evolution during annealing on different length scales, from the subgrain morphology of individual grains (using DFXM) to the aggregate behavior of several thousands of grains (using HEDM).

The mechanical and functional properties of polycrystalline materials have significant contributions from the 3D interaction of grains that form their micro-structure. Such grain maps can be extracted from existing characterisation techniques that utilise X-rays or electrons. However, complimentary techniques using neutrons have not yet developed to maturity. Furthermore, neutrons provide distinct advantages where, due to their lower attenuation, larger materials can be analysed, such as real-world engineering materials.

Here, a novel 3D grain mapping methodology, known as Trindex, has been demonstrated to reveal the micro-structure of a prototypical cylindrical iron material. While there already exist several methods on grain mapping with neutron imaging, Trindex provides a robust and relatively straightforward approach. Trindex is a pixel-by-pixel neutron time-of-flight reconstruction method which extracts the morphology of grains throughout the sample, in addition to their pseudo-orientations.

Experiments were performed at the SENJU beamline of the Japan Proton Acceleration Research Complex (J-PARC). For the setup, an imaging detector was placed behind the sample with diffraction detectors simultaneously collecting the backscattering from the sample. Such diffraction will be used to confirm grain orientations. Details of the methodology and the resulting 3D grain maps of materials will be presented.

1. Cereser, A., et al. "Time-of-flight three dimensional neutron diffraction in transmission mode for mapping crystal grain structures." Scientific reports 7.1 (2017): 1-11.
2. Peetermans, S., et al. "Cold neutron diffraction contrast tomography of polycrystalline material." Analyst 139.22 (2014): 5765-5771.

The properties and behaviour of materials (metals, alloys, semiconductors, ceramics, polymers, drugs, biomaterials) are to a large extent determined by their phase composition, particle size, crystallinity, stress, defects and crystallographic orientation (texture). Two-dimensional (2D) X-ray diffraction is one of the most appealing techniques for users who are interested in extracting every bit of information about their samples. 2D X-ray diffraction patterns, collected using area detectors contain detailed information about all these important material characteristics. Furthermore, the high sensitivity and resolution of modern detectors (e.g. PIXcel^3D, GaliPIX^3D) make possible the collection of relevant structural information within seconds. This allows following in real time transformation processes of materials, like recrystallization, deformation or phase transitions. XRD2DScan is the Malvern Panalytical software for displaying, processing, and analyzing 2D X-ray diffraction data. The latest version of the software (version 7.0) offers new features such as orientation and crystallite size analysis, image comparison, as well as scripting for easy automation. The application of the software to the characterization of complex anisotropic materials (liquid crystals, polymers, bone, wood, ...) will be illustrated through several examples.

A material responds to its surroundings via residual changes in its structure that change its corresponding properties. The macroscopic structural evolution is instigated by the dynamics of statistical populations of defects that move, interact, and pattern – causing atomic-scale defects to create 3D networks of boundaries that comprise the heterogeneous “real-world” materials. While techniques exist to probe material defects, they are mainly limited to surface measurements or rastered scans that cannot measure the dynamics of irreversible or stochastic processes characteristic of defect dynamics. In this talk, I will introduce time-resolved dark-field X-ray microscopy (tr-DFXM) as a new tool to capture movies that visualize dislocation dynamics in single- and poly-crystals at the mesoscale. I will start by describing the infrastructure we have developed to build and align the microscope, then to interpret and quantify the information captured in our movies. With this new tool, I will then demonstrate how dislocation patterns evolve at high temperatures in aluminum (Fig. 1). Tr-DFXM holds important opportunities for future studies on mesoscale dynamics, as it can inform models that have previously been refined only by indirect measurements and multi-scale models.

This work was performed in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The three-dimensional X-ray diffraction (3dxrd) technique provides a useful tool to investigate polycrystalline materials, grain-by-grain, in a non-destructive way. The approach of the scanning 3dxrd microscopy is to probe the sample by moving a pencil beam horizontally across it (y direction) with a resolution dependent on the beam size. For each step, the sample is rotated of 180° (or 360°, ω angle) in order to collect the diffraction spots of all the grains in the sample [1].

We used a combined approach of scanning 3dxrd and Phase Contrast Tomography (PCT) to investigate the hydration of a widespread hydraulic binder material, namely gypsum plaster. This material forms when the bassanite (calcium sulfate hemihydrate) reacts with water. In-situ 3dxrd measurements allowed to understand the crystallographic lattice, orientation and position of each grain in the sample during the hydration reaction (Figure 1 a,b).

The PCT reconstructions, instead, allowed the visualization of the shape of the crystals in the sample over time and a quantification of density and porosity (Figure 1 c,d).

Monitoring the evolution of the hydration reaction of gypsum plaster with both these techniques appears to be a promising tool to gain insights about the kinetics of the hydration reaction, the crystallization and growth of the hydrated phase and the shape of the final gypsum crystals that build the interlocked and porous gypsum plaster hardened mass.