Materials with negative thermal expansivity (NTE) attracts great attention of scientists because they can be combined with numerous materials with positive thermal expansion (PTE) in order to prepare a composite material with a tailored coefficient of thermal expansion, namely, zero expansion. This allows decreasing a performance deterioration caused by a large difference in expansion coefficients.[1] Among numerous metal-organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs) are highly popular because of the possibility to combine electronic properties of the transition metal ions with structural features of zeolites. They possess large porosity, therefore alkali metals that form dense and hyper coordinated structures stayed out of the focus for its synthesis. On the other hand, magnesium imidazolate has a porous structure, as well as its borohydride(s). Although the preparation of manganese imidazolates is challenging, probably due to the difficulties of formation of non-distorted tetrahedral Mn²⁺-4N geometry preferable in ZIFs, the similarity of magnesium and manganese borohydrides was reason to try synthesis with both metals and compare the results.

Mechanochemical reactions of alkali metal imidazolates and magnesium or manganese borohydride gave novel bimetallic imidazolates AMIm₃ (A=Na, K; M=Mg, Mn) whose crystal structures have been solved from synchrotron radiation X-ray powder diffraction (PXRD) data using global optimization in program FOX[2].Pores of 30-35 ų (5-6 % of the unit cell volume) are incorporated in all structures. Detailed study of temperature-aided structural and microstructural changes, obtained from the synchrotron in situ HT-PXRD data, gave a deeper understanding of crystallization processes in the borohydride-imidazolate system and have elucidated mechanisms of the reactions which occurs during mechanochemical synthesis and thermal treatment of these systems.

Extensive study of thermal expansion properties of a series of isostructural compounds AMIm₃ (A=Na, K; M=Mg, Mn) revealed a common behavior characteristic for a structural type. However, very interesting drastic changes of thermal expansion were noticed when alkali metal imidazolate (NaIm) coexist with compound-of-interest (NaMgIm₃); volumetric thermal expansion coefficient changes from positive α_V = 35 × 10⁻⁶ K⁻¹ to colossal negative values α_V = −460 × 10⁻⁶ K⁻¹ and linear thermal expansion changes from α = 34 × 10⁻⁶ K⁻¹ to α = -210 × 10⁻⁶ K⁻¹ (Figure 1). This is caused by coherent intergrowth, lattice mismatch, a tensile strain, and microstructural properties [3] of mentioned phases and leaves a possibility of design of the material with zero thermal expansivity.

[1] Ren, Z.; Zhao, R.; Chen, X.; Li, M.; Li, X.; Tian, H.; Zhang, Z.; Han, G. (2018) Nat. Commun. 123, 1638.

[2] Favre-Nicolin, V.; Černý, R. (2002) J. Appl. Crystallogr. 35, 734−743.

[3] Matěj, Z.; Kužel, R.; Nichtová, L. (2010) Powder Diffr. 25, 125-131.

The research was supported by OP RDE project No. CZ.02.2.69/0.0/0.0/18_053/0016976 International mobility of research, technical and administrative staff at the Charles University .

The financial support of the SNSF project (SCOPES) “Metal-Hydride Organic Frameworks (HOF) - new solids for gas adsorption and separation” is acknowledged.

Molecules can crystallise either in the presence or absence of the solvent used to crystallise them with a range of intermolecular interactions between both the molecule and the solvent occurring to sustain and propagate the crystal structure. Molecules that crystallise as solvates or clathrates could be considered as host-guest materials, but it is often unclear whether a guest-free material can be obtained by heating the solvated material. If the solvent can be removed this can, in turn, lead to vacant void spaces or a partially closed material that can be used to store a secondary guest (either a gas or secondary solvent). Understanding how these materials behave upon removal of the solvent contained within them is crucial in assessing their potential applications. With the CSD recently reaching 1 million deposited crystal structures [1] there is a large resource of untested solvate structures, which may provide inspiration for new guest-uptake materials.[2]

This work presents an attempt to further understand a previously reported family of halogen-functionalised organic molecules which has been reported in 3 distinct phases (two inclusion phases and one solvent-excluded phase)[3]. The two inclusion phases adopt a 2D halogen-bonding network propagated through a halogen-halogen bonded trimer. The work presented here, initially focusing on the bromine-functionalised host molecule, used liquid-assisted grinding to screen a series of solvents to identify desirable inclusion phases. The grinding experiments also identified a previously unreported inclusion phase. Thermal stability studies demonstrated that these inclusion phases transformed to the solvent-excluded phase upon heating. Further work has involved altering the halogen functionality (using fluorine, chlorine or iodine) to see how this affects the propensity to form the desired inclusion phases and the thermal stability of these phases, as well as exploring whether phase transformation can be observed when samples are exposed to a vapour environment.

Figure 1. Overview of the solvent-dependent phases of a family of halogen-bonded networks.

MOFs, COFs, and HOFs as highly ordered porous architectures attract wide interest owing to their broad potential of application in heterogeneous catalysis, storage, sensing, drug delivery, separation, etc.

Research of organic frameworks assembled by supramolecular interactions without metal or covalent bonds taking part in the framework construction has come in the focus of interest the most lately. A well-orchestrated interplay of supramolecular interactions, molecular inflexibility, and spatial effects characterize the non-covalently bonded organic frameworks. All mentioned aspects affect the molecular and crystal symmetries. We reported recently the preparations and structures of ionic hydrogen-bonded organic frameworks, their polymorphic and solvatomorphic forms were described [1]. Further attempts were made to prepare hydrogen-bonded organic frameworks, either ionic or neutral. Our systematic study inspired by the Maruoka type chiral phase-transfer catalysts resulted in some new series of solvatomorphic hydrogen-bonded organic framework materials. We will present (Fig. 1), that the most important aspects in the HOF formation include (1) the intramolecular interactions which are responsible for the inflexibility of the molecule, (2) the intermolecular interactions which are responsible for framework construction, (3) the terminal spacer groups for void formation, (4) the molecular symmetries which prove to be important in the tightening of the molecule, and (5) all the aforementioned features affect the crystal symmetry which may coincide with the molecular symmetry.

The presented work contributes to the understanding of hydrogen-bonded organic framework formation. It supports the still challenging design and preparation of framework structures with high porosity.

Figure 1. The most important aspects in the HOF formation.

[1] Horváth D. V., Holczbauer T., Bereczki L., Palkó R., May N. V., Soós T., Bombicz P. (2018) CrystEngComm, 20, 1779-1782.

This work was supported by the National Research, Development and Innovation Office-NKFIH through OTKA K124544 and KH129588.

Chirality is a property that real images are non-superimposable on their mirror images. The importance of chirality has commonly been known through drug incidents of thalidomide all over the world ₁ ^1, ₂ ². Chirality exists not only molecules, crystals, membranes and other objects in nature. Crystal chirality is derived from not only molecular chirality but also helical arrangement of molecules in crystals. In the latter case, even if achiral molecules are put in a right-handed or a left-handed helical arrangement in crystals, the crystals occur chirality. It has already been known that the same amount of left-handed and right-handed crystals are obtained when chiral crystals composed of achiral molecules are grown ₃³. Among crystals composed of achiral molecules, about 8% of them are chiral crystals, so it is very important to grow chiral crystals that have particular chirality. However, it is extremely difficult to grow only right-handed or left-handed crystals from achiral molecules. In this study, we succeeded in growing right-handed or left-handed crystals from achiral molecules.

We have focused on Triglycine sulfate (TGS) crystals composed of glycine and sulfuric acid (Figure 1(a)). We found that TGS with particular chirality has grown by doping with L-, or D-alanine (Figure 1(b)). L-alanine-doped TGS (LATGS) crystals showed left-handedness, while D-alanine-doped TGS (DATGS) crystals showed right-handedness (Figure 2). This is an extremely interesting phenomenon. We discuss that this phenomenon is derived from polarity because TGS is ferroelectricity. The relationship between chirality and polarity helps the elucidation of the explicit mechanism of preferred chirality of TGS crystal by alanine.

While small molecule activation processes underpin transformations in catalysis, gathering structural information about the reactive metal-based species responsible can be challenging. Such species are often coordinatively unsaturated or possess labile ligands; they are therefore highly reactive and transient. Building on research trapping reactive species within the cavities of supramolecular assemblies or frameworks,[1] we have been using metal-organic frameworks (MOFs) to "matrix isolate" and structurally characterise catalytically important metal-based species.[2, 3] The building block synthetic approach of MOFs using chemically mutable links, coupled with long range order (crystallinity), and excellent chemical and thermal stability,[4] allows them to be used to stabilise and characterise reactive species.

To garner these insights we use a bespoke, flexible Mn-based MOF, [Mn₃L₂L’] (MnMOF-1, where L = bis-(4-carboxyphenyl-3,5-dimethylpyrazolyl)methane) with a site poised for allowing single crystal-to-single crystal (SCSC) post-synthetic metalation.[2, 3] This contribution will expand these ideas and examine ligand exchange chemistry occurring at trigonal planar Cu(I) sites chemically isolated in the MOF.[5] Insights into catalysis obtained by structurally characterising the initial catalysts and by targeting sequential “snapshots” of the catalytically active structure by single crystal X-ray crystallography will be reported.

1. R. J. Young, M. T. Huxley, E. Pardo, N. R. Champness, C. J. Sumby and C. J. Doonan, Chem. Sci., 2020, 11, 4031-4050
2. W. M. Bloch, A. Burgun, C. J. Coghlan, R. Lee, M. L. Coote, C. J. Doonan and C. J. Sumby, Nat. Chem., 2014, 6, 906-912; A. Burgun, C. J. Coghlan, D. M. Huang, W. Chen, S. Horike, S. Kitagawa, J. F. Alvino, G. F. Metha, C. J. Sumby and C. J. Doonan, Angew. Chem. Int. Ed., 2017, 56, 8412-8416; R. A. Peralta, M. T. Huxley, R. J. Young, O. M Linder-Patton, J. D. Evans, C. J. Doonan and C. J. Sumby, Faraday Discussions, 2020, 225, 84-99.
3. R. A. Peralta, M. T. Huxley, J. D. Evans, H. Cao, M. He, X. S. Zhao, S. Agnoli, C. J. Sumby and C. J. Doonan, J. Am. Chem. Soc., 2020, 142, 13533-13543; R. A. Peralta, M. T. Huxley, Z. Shi, Y.-B. Zhang, C. J. Sumby and C. J. Doonan, Chem. Commun., 2020, 56, 15313-15316.
4. H. Furukawa, K. E. Cordova, M. O’Keeffe and O. M. Yaghi, Science, 2013, 341, 1230444.
5. R. A. Peralta, M. T. Huxley, J. Albalad, C. J. Sumby and C. J. Doonan, unpublished results, 2021.

In recent years, convergent-beam electron diffraction (CBED) has been widely used for refining crystal structure parameters and low-order structure factors. It enables nanometer-scale structure analysis with high sensitivity to the distribution of valence electrons. The determination of low-order structure factors with higher precision is essential to precisely determine the chemical bonding state of materials which are closely related to their physical properties. Till date, it is considered that refinement of structure factors using CBED pattern taken at the Bragg-excited condition increases the sensitivity to the corresponding structure factor [1]. However, the origin of precision and correspondence between precision and sensitivities of CBED patterns in the refinement of structure factors, is still lacking.

In this analysis, a local structure analysis method developed by Tsuda and Tanaka [2] has been applied to potassium tantalate KTaO₃ (KTO). Isotropic atomic displacement parameters and five low-order structure factors were refined using energy-filtered CBED patterns taken at three zone-axis (ZA) and five Bragg-excited conditions. Compared to ZA patterns, the Bragg-excited CBED patterns showed higher precision in the refinement of structure factors. One to one correspondence between higher precision and sensitivity of Bragg-excited CBED pattern has been found only for structure factors of the outer zeroth-order Laue zone (ZOLZ) reflection having larger reciprocal lattice vectors. Smaller correlation coefficients among the refined structure factors in the refinement of Bragg-excited patterns lead to higher precision. From the point of view of higher precision, Bragg-excited patterns are advantageous over ZA patterns. To achieve higher precision and sensitivities in the refinements of structure factors it would be better to use both of the ZA and Bragg-excited CBED patterns. The use of large angle CBED (LACBED) or large angle rocking beam electron diffraction (LARBED) techniques should be effective for this purpose.

[1] Ogata, Y., Tsuda, K. & Tanaka, M. (2008). Acta Cryst. A64, 587.

[2] Tsuda, K. & Tanaka, M. (1999). Acta Cryst. A55, 939.

Phyre2 is a web server to predict protein structure from sequence (www.imperial.ac.uk/phyre2) that processes ~1,000 individual sequences submitted by users every day. Since its introduction in 2011, Phyre2 has processed well over 4M jobs with ~55,000 unique users per year, each submitting ~20 sequences on average. The Phyre2 (Fig 1) web portal [1]provides both a rapid and user-friendly interface to predict protein structure using homology based template modelling and also resources for analysing the results. The papers describing Phyre2 and its predecessors (3D-PSSM and Phyre) have had over 12,000 citations in the literature.

The performance of different protein structure prediction implementations is compared in a biennial exercise, the Community Wide Experiment on the Critical Assessment of Techniques for Protein Structure Prediction; the 14th edition, CASP14, took place in 2020 [2]. The outstanding performance of one program, AlphaFold2 [3] in CASP14 drew the attention of the world's media to this field. The results might lead the casual observer to conclude that the protein structure problem is solved, but at the moment AlphaFold2 itself is not readily accessible to the vast majority of users and the underlying methods employed have not yet been revealed in any detail.

We will show how the carefully designed interface to Phyre2 allows users to generate 3D protein structures from their sequence data in a flexible and straightforward way that makes good models readily available to the community at large.

In addition to a simple mode that allows modelling from single sequences, the Phyre2 web portal proves a range of extra functionality: i) a facility for batch submission of processing of proteomes, ii) searching model genomes for a protein structure, iii) PhyreAlarm, which automatically updates a user if a superior model can be predicted as a result of a newly-deposited structure in the protein data bank, and iv) facilities to analyse a predicted model in terms of accuracy and sequence conservation.

Phyre2 is a resource with the UK node of ELIXIR, the European–wide network of bioinformatics facilities.

Fig 1 – Main results page of the Phyre2 web server showing hits with confidence scores and origin of templates

[1] Kelley et al. (2015) Nature Protocols, 10, 845.

[2] CASP14, https://www.predictioncenter.org/casp14/index.cgi

[3] see, e.g. https://en.wikipedia.org/wiki/AlphaFold

Today the study of two-dimensional (2D) materials has become one of the key objectives of materials science. Unlike their three-dimensional counterparts, 2D materials can simultaneously demonstrate unique transport and mechanical properties due to their dimensionality and quantum size effect. Weak van der Waals interaction between layers in heterostructures of 2D materials, electron confinement inside the layers, and high surface-to-volume ratio lead to remarkable changes in electronic and optical properties of the materials, as well as in their chemical and mechanical response. Besides, a wide range of ways to tune properties using lateral and vertical heterostructures fabrication, chemical functionalization, strain, defect and substrate engineering, makes 2D materials ideal candidates for developing a new class of electronic devices. In their fabrication and application, 2D materials are usually located on top of the substrate or combined into heterostructures, which makes their structures and properties strongly depend on the nature and quality of the environment. Here, we present a novel method for studying the atomic structures of two-dimensional materials and epitaxial thin films on arbitrary substrates. The method can predict successful stages of epitaxial growth and the regions of stability of each atomic configuration with experimental parameters of interest (Figure 1). We demonstrate the performance of our methodology in the prediction of the atomic structure of MoS₂ on Al₂O₃ (0001) substrate. The method is also applied to study the CVD growth of graphene and hexagonal boron nitride on Cu (111) substrates. In both cases, stable monolayer and multilayer structures were found. The stability of all the structures in terms of partial pressures of precursors and temperature of growth is predicted within the ab initio thermodynamics approach.

Prediction of crystal structures has reached a high level of reliability, but much less is known about the mechanisms of structural transitions and pertinent barriers. The barriers related to nucleation of crystal structure inside another one are critically important for kinetics and eventually decide what structure will be created in experiment.

We show here an NPT metadynamics simulation scheme [1] employing coordination number and volume as collective variables and illustrate its application on a well-known example of reconstructive structural transformation B1/B2 in NaCl. Studying systems with size up to 64000 atoms we reach beyond the collective mechanism (Fig.1 (a)) and observe the nucleation regime (Fig.1 (b)). We reveal the structure of the critical nucleus and calculate the free-energy barrier of nucleation and also uncover details of the atomistic transition mechanism and show that it is size-dependent.

Our approach is likely to be applicable to a broader class of structural phase transitions induced by compression/decompression and could find phases unreachable by standard crystal structure prediction methods as well as reveal complex nucleation and growth effects of martensitic transitions.

Figure 1. (a) Collective mechanism - A typical frame of supercell during the course of the B1/B2 transition in NaCl at 40 GPa and 300 K in the system of size of 512 atoms. (b) Nucleation - A typical nucleus of the B2 phase in the B1 phase (with shape of ellipsoid), during the transition at 40 GPa and 300 K in the system of 64 000 atoms. Plane of view cuts the ellipsoid through its centre. Figure was produced using OVITO [2].

[1] M. Badin and R. Martoňák, arXiv:2105.02036

[2] A. Stukowski, Modelling Simul. Mater. Sci. Eng. 18, 015012 (2010).

Keywords: pressure-induced phase transitions; nucleation; martensitic transition; metadynamics

This work was supported by the Slovak Research and Development Agency under Contracts APVV-15-0496 and APVV-19-0371, by VEGA project 1/0640/20 and by Comenius University under grant for young researchers - UK/436/2021.

Metal nanocatalysts typically consist of noble metal nanoparticles (NPs) anchored on a metal oxide support, where the NP surface exposes active sites to catalyse target chemical reactions. The catalyst’s economic viability demands high activity, high selectivity, and high stability. It is well established that the performance of catalytic NPs is closely related to their size, shape and interparticle distance. Synthesis methods that can tailor the structural properties of noble metal NPs are therefore attractive to elucidate performance-structure relationships. In this regard, there is an increasing interest in Atomic Layer Deposition (ALD), a vapour-phase deposition method which proved its efficiency in dispersing noble metal NPs on complex high surface area supports with atomic-scale control over the metal loading (atoms per cm²) and nanoparticle size [1]. However, an improved understanding of how the deposition parameters influence the formation and growth of the noble metal NPs is required to fully exploit the tuning potential of ALD.

We designed a high-vacuum setup for thermal and plasma-enhanced ALD that is compatible with synchrotron-based in situ X-ray fluorescence (XRF) and grazing incidence small-angle X-ray scattering (GISAXS) monitoring [2]. Using this setup, we resolved the dynamics of Pt and Pd NP formation and growth on planar SiO₂ and Al₂O₃ surfaces [3-5]. In situ XRF was used to quantify the evolution of metal loading with the number of ALD cycles, while analysis of the key scattering features allowed us to correlate the amount of deposited material with the evolution of structural parameters such as cluster shape, average size and areal density.

In a first study we focused on the growth of Pt deposits on SiO₂ with the thermal ALD process comprising sequential MeCpPtMe₃ and O₂ exposures at 300°C [3]. The results indicated a nucleation stage, followed by a diffusion-mediated particle growth regime during which the size and spacing of the Pt NPs is largely determined by adsorption of migrating Pt species on the surface and diffusion-driven particle coalescence. Interestingly, diffusion phenomena and ripening of the Pt NPs during ALD could be suppressed by using N₂ plasma as a reactant instead of O₂ in the ALD cycle. By combining O₂-based and N₂ plasma-based ALD processes, we developed a tuning strategy that offers independent control over the Pt NP size and areal density [4].

Secondly, we studied the initial nucleation of Pd NPs deposited at 150°C on oxide substrates (SiO₂ or Al₂O₃) by combining Pd(hfac)₂ and H₂ plasma in an ALD sequence [5]. The results confirmed a long nucleation process and revealed a relatively low NP areal density, in line with the occurrence of surface poisoning during the initial ALD cycles [6]. The reaction of the Pd precursor with the oxide surface leaves site blocking surface species behind, thereby inhibiting the nucleation. To enhance the nucleation, we explored two potential methods to ‘clean’ the surface: (1) introducing trimethylaluminum (TMA) exposures during the initial ALD cycles, and (2) introducing an O₂ plasma exposure, either before or after the H₂ plasma step, throughout the ALD process. Both these approaches had a significant impact on the evolution of NP size and spacing, and the insights obtained were used to develop a strategy that enables precise control of the Pd NP dimensions and coverage [5].

[1] Lu, J., Elam, J. W. & Stair, P. C. (2016). Surf. Sci. Rep. 71, 410.

[2] Dendooven, J., Solano, E., Minjauw, M. M., Van de Kerckhove, K., Coati, A., Fonda, E., Portale, G., Garreau, Y. & Detavernier, C. (2016). Rev. Sci. Instrum. 87, 113905.

[3] Dendooven, J., Van Daele, M., Solano, E., Ramachandran, R. K., Minjauw, M. M., Resta, A., Vlad, A., Garreau, Y. Coati, A., Portale, G. & Detavernier, C. (2020). Phys. Chem. Chem. Phys. 22, 24917.

[4] Dendooven, J., Ramachandran, R. K., Solano, E., Kurttepeli, M., Geerts, L., Heremans, G., Rongé, J., Minjauw, M. M., Dobbelaere, T., Devloo-Casier, K., Martens, J. A., Vantomme, A., Bals, S., Portale, G., Coati, A. & Detavernier, C. (2017). Nat. Commun. 8, 1074.

[5] Feng, J.-Y., Ramachandran, R. K., Solano, E., Minjauw, M. M., Van Daele, M., Vantomme, A., Hermida-Merino, D., Coatia, A., Poelman, H., Detavernier, C. & Dendooven, J. (2021). Appl. Surf. Sci. 539, 148238.

[6] Goldstein, D. N. & George, S. M. (2011). Thin Solid Films 519, 5339.

Soft-matter bicontinuous networks find a double gyroid structure from block copolymer (BCP) self-assembly. A gyroid structure composed of dissimilar blocks has proven its potential as a soft crystal, of which the lattice dimension is variable with molecular weight of the polymer. Using an asymmetric polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA), recently we showed that the self-assembled gyroid films formed via a solvent vapor annealing (SVA) process undergo unique structural distortion due to directional deformation immediately upon deswelling [1]. During the SVA process with PS-b-PMMA films, initially transient cylinders developed from the as-cast morphology transform into a cubic gyroid structure in a swollen state. We then observed that upon solvent evaporation the gyroid lattice contracts along the film normal direction while retaining the swollen lateral dimension. The degree of contraction is turned out to be related to the evaporation speed. Rapid and spontaneous deswelling processes lead to triclinic gyroid structures with z-directional contraction ratios (C_z) of 2.5 and 2.0, respectively.

Our X-ray analysis reveals that symmetries of the resulting gyroid structures are partially broken due to the non-affine transformation, eliciting several forbidden reflections such as {110} and {200} reflections. For further characterization of the symmetry-breaking, we delineate the structural features of noncubic gyroid films by computing electron-density difference maps from grazing incidence small angle X-ray scattering (GISAXS) data. We employed iterative phase retrieval method to solve the phase problem. Level-set approach is accordingly developed to quantitate the structural characteristics of the maps in terms of inversion symmetry-breaking, suggesting its possible application to optical Weyl photonic crystals. This presentation will focus on X-ray data collection and analysis.

[1] Jo, S., Park, H., Jun, T., Kim, K., Jung, H., Park, S., Lee, B., Lee, S., Ryu, D. Y. (2021), Applied Materials Today 23, 101006.

GISAXS measurements were performed at Pohang Accelerator Laboratory (Korea) and Advanced Photon Source (APS) at Argonne National Laboratory (US). The APS is supported by the US department of Energy, Office of Basic Energy Sciences, under contract no. DE-AC0206CH11357. This research was supported by Samsung Research Funding & Incubation Center of Samsung Electronics under Project Number SRFC-MA1801-04.

Thin films of thickness 100 nm or less are typically deposited on a much thicker substrate, making it difficult to obtain the required high-quality total scattering data for analysis in real-space with pair distribution functions (PDF) [1]. In recent years, total scattering in reflection geometry at grazing incidence (GI), that is, below the critical angle of total external reflection, has been used with success to increase the surface sensitivity and scattering intensity [2, 3]. GI-PDF gives high-quality PDFs from films as thin as 3 nm with a 20 x 2.5 µm² focused X-ray beam with 100 keV photon energies at PETRA III [2]. Using this same setup we have developed a novel ultra-high vacuum compatible deposition chamber, that allows for the demanding sample alignment of the thin film sample under vacuum conditions as well as a 180 degree in-plane rotation [4]. Via a rotary feedthrough and bellows combination the surrounding vacuum chamber is not affected by translation of the sample, allowing for film deposition equipment such as a magnetron sputter source. This has been employed at the P07-EH2 beamline with a radio-frequency magnetron sputter source, as pictured in the figure below. We will show how this has been applied to observe the formation of thin films during the initial stages of deposition in real time with sub-second time resolution.

[Fig 1 with figure + picture]

Figure 1. PDFs of a Pt thin film at 10, 20, 30, 40, 50 and 60 seconds of sputter deposition with approximately 1 Å/s and a picture of the equipment installed on the surface diffractometer at beamline P07-EH2, PETRA III, Hamburg, Germany, as seen from the detector side.

[1] K. M. Ø. Jensen et al., IUCrJ 2 (2015), 481

[2] A.-C. Dippel et al., IUCrJ 6 (2019), 291

[3] K. Stone et al., APL Materials 4 (2016), 076103

[4] M. Roelsgaard et al., IUCrJ 6 (2019), 299

Jana2020 is a new program for solving and refining regular, modulated and magnetic structures. The lecture will present new possibilities of this program in the field of magnetic structures.

In the last three years, a series of developments within the FullProf Suite [1], concerned with magnetic structures (both commensurate and incommensurate), have been performed. From the the first publication describing shortly the program FullProf [2] in 1993 many changes and re-writing of the code were done. In particular, the phase convention in the expression of the magnetic structure factor were changed. In 1993, we introduced for the first time the Simulated Annealing (SAnn) procedure for solving magnetic structures in a program called MagSan [2] that was later developed for incommensurate structures and embedded within FullProf. The method to make a symmetry analysis during many years was based in the Bertaut’s and Izyumov proposals [3-5] and we developed the program BasIreps to help the a priori construction of magnetic models to be refined. The use of magnetic space groups (MSG) was possible but, in the absence of appropriate tables or computing tools, the user had to construct the symmetry operators by hand. The treatment of incommensurate magnetic structures either was only possible by using basis vectors of irreducible representations or by constructing a series of 3D operators accompanied by a phase factor that was done by looking at the output of BasIreps and completing the information if the user was able to understand group theory.

The availability of new tools on the Web [6-8] and the creation of the Commission on Magnetic Structures of the IUCr has allowed the development of precise and unambiguous ways of describing magnetic structures using MSG and magnetic superspace groups (MSSG) [8, 9] by mean of magnetic CIF files. The team working in the FullProf Suite has accompanied these developments and created new tools to import these CIF files and convert them to input control files for FullProf. We have now the possibility of treating MSSG within FullProf with up to three independent modulation wave vectors, both for powders and single crystals, with automatic symmetry constraints determination for the amplitudes of modulations [10]. The displacement and thermal amplitudes are implemented but, for the moment, the calculation of structure factors using integration in internal coordinates is not yet available.

One important feature of FullProf is the use of SAnn, using the full powder diffraction pattern in which the components of the magnetic amplitudes are free parameters, in either crystallographic or spherical settings. This is very important for the powder case in which the loss of information may give rise to ambiguous or degenerate solutions. Moreover, the SAnn method may be used as an alternative to refinement because in such cases the least-squares refinement procedure diverges or it is unable to arrive to convergence.

In this talk, after summarizing the full set of changes performed during the last years (interoperability with the Bilbao Crystallographic Server [6, 7] and ISODISTORT [8], the use of magnetic Hall symbols [11], magnetic symmetry modes, etc.) I will present few recent examples of the use of FullProf in the magnetic structure determination of magneto-electric and multiferroic materials.

[1] https://www.ill.eu/sites/fullprof/

[2] Rodriguez-Carvajal J. (1993). Physica B. 192, 55.

[3] Bertaut E.F. (1968). Acta Cryst. A24, 217.

[4] Izyumov Yu. A., Naish V.E. and Ozerov R.P. (1991), Neutron Diffraction of Magnetic Materials, New York: Consultants Bureau.

[5] Rodriguez-Carvajal J. and Bourée F. (2012). EPJ Web of Conferences 22, 10, https://doi.org/10.1051/epjconf/20122200010.

[6] Aroyo M.I., Perez-Mato J.M., Capillas C., Kroumova E., Ivantchev S., Madariaga G., Kirov A. & Wondratschek H. (2006), Z. Krist. 221(1), 15.

[7] Aroyo M.I., Kirov A., Capillas C., Perez-Mato J.M. & Wondratschek H. (2006), Acta Cryst. A62, 115. http://www.cryst.ehu.es.

[8] Campbell B.J., Stokes H.T., Tanner D.E. & Hatch D.M. (2006), J.Appl.Cryst 39, 607. http://stokes.byu.edu/iso/isotropy.php

[9] Perez-Mato J.M., Ribeiro J. L., Petricek V. and Aroyo M. I. (2012), J. Phys.: Condens. Matter 24, 16320.

[10] Rodriguez-Carvajal J. and Villain J. (2019). C.R. Physique 20, 770, https://doi.org/10.1016/j.crhy.2019.07.004.

[11] González-Platas J., Katcho N.A. & Rodriguez-Carvajal J. (2021). J.Appl.Cryst 54, 338

Keywords: magnetic structures, simulated annealing, superspace groups

I thank my colleagues of the Diffraction Group at ILL and all the users of the FullProf Suite for the help in improving the programs.

MagStREXS is a crystallographic software dedicated to the analysis of resonant elastic X-ray scattering (REXS) diffraction data for the determination of magnetic structures that is under development at beamline P09 at PETRA III (DESY).

REXS is a powerful and element specific technique to study charge, spin, and orbital ordering in solids and thin films. Different types of data can be collected in a REXS experiment, although the analysis of these data is complex. The aim of MagStREXS is to facilitate this type of analysis to the non-specialist in this technique, and also to provide tools for the preparation of these experiments.

In this talk an overview of MagStREXS will be presented, together with some magnetic structures that have already been determined with it.

Lanthanide ions play a crucial role in various research fields. Much theoretical effort, that aims understanding and enhancing magnetic anisotropy in multiferroics and molecular magnetic materials, shows that the variation of magnetisation anisotropy is accompanied by important changes of 4f-electron, spin and orbital distributions. However, the experimental determination of the shape of these distributions is a non-trivial task especially in the case of unquenched orbital moment. Here, the procedure of magnetisation density reconstruction in lanthanides with unquenched orbital moment is developed, based on the iterative entropy maximization and the site susceptibility approach. The calculation were performed by recently developed code written as part of a crystallographic CrysPy library [1].

We illustrate the possibilities of the method by the first joint magnetisation density reconstruction and susceptibility refinement of locally anisotropic lanthanide pyrochlores RTi2O7 (R=Tb, Ho, Er and Yb) [2]. An oblate asphericity of Tb3+ density and prolate these of Ho3+ and Yb3+ was revealed (fig.1). Reconstructed distributions and refined susceptibility parameters are compared with these predicted by the crystal field theory in frame of single ion anisotropy model using McPhase software [3].

1. GitHub page of CrysPy library: https://ikibalin.github.io/cryspy/
2. H. Cao et al. Phys. Rev. Lett. (2009) 103, 056402
3. M. Rotter et al J. Phys.: Conf. Ser. (2011) 325 012005.

Magnetic x-ray standing waves (MXSW) - a combination of x-ray standing waves (XSW) [1] and x-ray magnetic circular dichroism (XMCD) - is a new method for direct investigation of magnetic structure of crystals and thin films on the atomic level. In the regular XSW technique a standing wave emerging in the region where incoming and Bragg reflected waves interfere is employed to study atomic positions in element specific manner. The standing wave has a periodicity of the lattice and moves by half of its period as the sample is rocked through the reflection domain. This movement across the lattice causes modulations in the amount of emitted fluorescence - their character is characteristic for a distribution of given atomic kind. This gives - in contrary to diffraction methods - a direct, element specific structural information. In MXSW, additional magnetic sensitivity is achieved by using circularly polarised incoming wave and magnetising the sample. The normalised difference between fluorescence yields recorded for each helicity/magnetic field orientation (XMCD signal) is proportional to the distribution of magnetic atoms and their magnetic moments. This makes MXSW site, element and magnetic sensitive method.

The theoretical framework of MXSW method is based on dynamical theory of x-ray diffraction and time-dependent perturbation theory. The first is used to describe the phenomena of the scattering of x-rays by the crystal lattice and yields a form of the wavefield inside the crystal for circularly polarised incident wave. The latter provides a tool to evaluate the absorption cross-section for the considered wavefield. What is obtained finally is an angular dependence of XMCD signal, which similarly as a single fluorescence yield in XSW method, exhibits variations dependent on the distribution of magnetic atoms.

The Fig. 1 shows an exemplary, simulated MXSW signal for the magnetite crystal, (004) reflection. The insets present schematically the magnetic structure and the positions of the standing wave at the low (marked by green colour) and high (blue) angular side of the reflection domain. Iron ions in the magnetite structure are arranged in two sublattices – octahedrally (marked by blue colour) and tetrahedrally (green) coordinated ones. Since the magnetic moment on each of two sublattices is different and oriented opposite, the contribution of the sublattices to the overall XMCD signal changes depending on the position of the nodes and antinodes of the standing wave. The variations are characteristic for this arrangement of the iron atoms and their shape would be different for any other one. Therefore, the MXSW signal directly provides information about the magnetic structure.

The first experiment aiming at proving the feasibility of the method and confirming the established theory was performed at PETRA III synchrotron on the single crystal sample of Pt₃Co alloy. The measurements were conducted at the Pt L₃ absorption edge. A clear variation in XMCD signal of the magnetic origin was observed. As a next step, an experiment on magnetite is planned to show the power of the method to probe the arrangement of the magnetic ions.

[1] Zegenhagen, J., Kazimirov, A., The X-Ray standing Wave Technique: Principles and Applications (2013).

The local minima of optimized non-linear functions are a reason for ambiguity of the obtained solutions in crystal structure analysis and magnetic structure analysis (Figure 1). In this study [1], semidefinite programming relaxation (SDR) was applied for the first time to the determination of magnetic structure. Use of SDR allows us the following things (i) completing the global optimization procedure in a very short time (less than several seconds in many cases), (ii) judging whether the obtained solution is truly global one, there are multiple good candidates, or the irreducible representations considered are wrong with 100 % probability. The solid foundation is provided by the duality theorem for convex optimization problems (Figure 2).

In general, the global optimization of SDR is applicable for estimating not only magnetic moment vectors but also atomic occupancies at a fixed set of coordinates x₁, …, x_m from the absolute values of structure factors. Therefore, the method can be also used to judge if x_i is an atomic site or a void.

In many cases, this problem has a unique minimum solution. In some cases, there are a few distinct solutions, all of which can be constructed from the output of SDR. In a very few cases, the existence of multiple solutions is suggested by the SDR result. This often occurs when the atomic coordinates x₁, …, x_m in the unit cell are periodic or almost periodic as in Figure 3. If the symmetry of the atomic coordinates is considered, the existence of such multiple solutions can be largely eliminated.

As a result, SDR can provide a numerical answer to the classical problem of the uniqueness of solutions in crystal structure analysis [2]. Global optimization of the SDR method is now being implemented into Z-Rietveld software [3] distributed for users of J-PARC (Japan Proton Accelerator Research Complex).

Laser Powder bed fusion (L-PBF) has attracted a lot of interest in recent years, not only for its profound advantage of producing metallic components of complex geometries but also for the possibility of manipulating microstructures and crystallographic textures. Additionally, recent observations on wrought austenitic steels have revealed the strong dependence of the transformation induced plasticity (TRIP) effect in metastable stainless steels on the crystallographic texture [1–3]. Taking the aforementioned observations into consideration, we can now process TRIP steels such as 304L by L-PBF, in order to produce differently textured specimens and manipulate the TRIP effect. In this contribution, in situ uniaxial tension and compression tests with neutron diffraction, are utilized for monitoring of the microstructural evolution during deformation. The present study highlights how different microstructures, produced by L-PBF, lead to different deformation behavior in austenitic stainless steels and paves the way for tailored microstructures in different types of steels and for studies under different loading conditions.

References

[1] E. Polatidis et al., “The interplay between deformation mechanisms in austenitic 304 steel during uniaxial and equibiaxial loading,” 2019, doi: 10.1016/j.msea.2019.138222.

[2] E. Polatidis et al., “Suppressed martensitic transformation under biaxial loading in low stacking fault energy metastable austenitic steels,” Scr. Mater., vol. 147, pp. 27–32, Apr. 2018, doi: 10.1016/j.scriptamat.2017.12.026.

[3] E. Polatidis, J. Čapek, A. Arabi-Hashemi, C. Leinenbach, and M. Strobl, “High ductility and transformation-induced-plasticity in metastable stainless steel processed by selective laser melting with low power,” Scr. Mater., vol. 176, pp. 53–57, Feb. 2020, doi: 10.1016/j.scriptamat.2019.09.035.

Phase transformations in a single crystal of a metastable β titanium alloy (Ti-15Mo in wt %) were investigated in situ during heating by synchrotron x-ray diffraction. Metastable β titanium alloys contain such type and amount of alloying elements that the high‑temperature β phase (body-centred cubic) can be retained in a metastable state during fast cooling to room temperature; i.e. the formation of low-temperature α phase (hexagonal close-packed) is prevented. Ti alloys from this class generally undergo a wide range of phase transformations due to their metastable nature. First, nano-sized particles of metastable ω phase form in this class of Ti alloys during fast cooling by a difusionless displacement mechanism, which can be characterized as a collapse of neighbouring (111)_β planes into their intermediate position. During ageing or heating, ω particles grow by a combined displacement and diffusion process which is accompanied by rejection of alloying elements from the ω phase into the surrounding β matrix. At higher temperatures, lamellae of the thermodynamically stable α phase precipitate in the material; this process can be assisted either directly or indirectly by the previous β+ω microstructure.

In situ x-ray diffraction was measured using 60 keV photons at the high-energy beamline ID11, ESRF, Grenoble, France. This experiment was performed using an oriented single crystal of Ti-15Mo prepared in an optical floating zone furnace. A slice of the single-crystalline material with the [100]_β crystallographic axis parallel to the primary beam was placed in a special quartz chamber furnace which allowed measuring in a high vacuum. X-ray diffraction patterns were acquired in situ during heating with a constant heating rate of 5 °C/min.

Fitting of the temperature dependence of intensity of selected representative single-crystalline diffraction spots showed that at the beginning of linear heating, up to approximately 350°C, the volume of ω phase decreased, which is likely connected with displacement-accompanied ω to β reversion. Between 350°C and 420°C, the volume fraction of ω particles increased which is the consequence of diffusion-driven coarsening of ω phase particles. Subsequently, as the temperature approached the stability limit of the ω phase, the volume of ω decreased. A complete dissolution was observed at 560°C. Finally, a rapid growth of the α phase commenced at about 580°C. It was also verified that during linear heating, none of the crystallographic variants of ω and α phase is preferred.

Many mechanical structures are submitted to repeated loadings during their life span and can break under stress lower than the ultimate tensile stress. This phenomenon, called fatigue of materials, has attracted the scientific community attention due to its effect in many industrial sectors, such as the transport, aeronautic and energy. Fatigue design is thus crucial in engineering and it requires the accurate characterization of material behavior under cyclic loadings to ensure the safety and reliability of structures throughout their life. It is presently common to find mechanical systems subjected to several billion cycles, in what is called the gigacycle fatigue domain or very high cycle fatigue (VHCF) domain [1]. The characterization of the fatigue behavior of materials have been largely investigated with fatigue tests requiring long testing time with standard laboratory. To overcome this inconvenient new approaches using ultrasonic fatigue machines have been developed during the last decades. In particular, the present research group developed recently a new method for the fast determination of fatigue behavior interpreting diffraction patterns with a temporal resolution of ∼1 µs during an ultrasonic fatigue test and loading frequency of about 20 kHz. The present study points on the estimation of the amount of energy stored by the specimen during its deformation due to an ultrasonic fatigue loading. This energy is a crucial parameter as it is strictly related to the fatigue damage and can be estimated from the intrinsic dissipation and the mechanical work supplied to the specimen. X-ray diffraction analysis were performed to measure the supplied work by integrating over one fatigue cycle of the product of the strain rate by the stress. In particular, pure copper and steel specimens were loaded using a 20 kHz ultrasonic fatigue machine mounted on the six-circle diffractometer available at the DiffAbs beamline on the SOLEIL synchrotron facility in France. Then, in order to obtain the mechanical work: 1) from the shift of Bragg peaks is possible to estimate the total stress applied to the sample, 2) from both the broadening and shift of peaks one can measure the mean elastic lattice strain distribution, and 3) from the peak broadening the fluctuation of elastic strain is deduced, providing information about intragranular strain heterogeneity and dislocation density.

[1] Bathias, C. & Paris, P. (2005). Gigacycle Fatigue in Mechanical Practice. New York: Marcel Dekker.

Important problem studied in this work is the anisotropy of mechanical properties for textured polycrystalline materials. The mechanical behaviour during in-situ loading tests for magnesium AZ-31 alloy was studied using neutron diffraction. The lattice strains were measured during tensile by using angle-dispersive neutron diffraction (TKSN 400 at NPI in Řež, Czech Republic) and changing sample orientation with respect to the scattering vector. The measurements were done for sets of poles corresponding to different orientations of the grains in strongly textured Mg alloy. Subsequent experiment was performed using time of flight (TOF) neutron diffraction at the pulsed reactor IBR-2 in Joint Institute for Nuclear Research (Dubna, Russia), using EPSILON-MDS instrument equipped with 9 detectors. The experiments allowed to develop an experimental methodology based on the so-called crystallite group method in order to determine the evolution of the stresses localised in polycrystalline grains having different crystallographic orientations. The components of stress tensor were determined directly from measured lattice strains corresponding to chosen orientations of crystallite lattice.It was found that the crystallites having two main orientations, named A and B, are harder when compared with other ones. For these orientations the basal slip system cannot be activated because the load is applied in direction parallel to the basal plane. Orientation B was completely transformed to twins (having T orientation) during the compression test. In the case of the soft orientations C and D, the direction of the load is inclined from the basal plane, i.e. the basal system can be activated. Using the experimental data the evolution of stress tensor and von Mises stress were determined for selected groups of grains. A large difference in the hardness of crystallites having different lattice orientations was found. The highest von Mises stress appeared on twins, which was compensated by low stresses localised on soft orientations C and D.

The novelty of our study is in original methodology used for direct determining of stress tensor for groups of polycrystalline grains having different orientations (especially for preferred texture orientations). The stress evolution measured during sample loading allowed us to find out the critical resolved shear stress (CRSS) values for different slip systems and twinning process.

Research on lead-free piezoceramics is a trending topic [1]. A significant component of this search is the characterization of the effect of texture on the properties of polycrystalline electroceramics. The present contribution describes an integrated methodology, systematized in a software package, to solve the following tasks: (a) interpretation by numerical simulation of XRD patterns produced by textured samples; (b) forecast of the effective elasto-electrical properties of piezoceramics, starting from the knowledge of the corresponding single-crystal tensors and the texture determined in (a).

Part (a) considers 1D and 2D diffraction experiments, with Bragg-Brentano, grazing incidence and transmission geometries. The inverse pole figure of the symmetry axis of fiber-textured piezoceramics is proposed and refined by a Rietveld-type procedure [2].

The calculations in part (b) are performed using a variant of the Voigt-Reuss-Hill approximations. Particular precautions are taken with regard to the selection of the quantities considered as independent variables [3].

The computer programs developed to solve the proposed tasks are shown, the use of the MPOD database [4] in this type of work is described, and representative case studies are presented.

Fig. 1 shows as an example the computerized modelling of the variation of the representative longitudinal surfaces of the elastic compliance s(h) and the charge constant d(h) of the lead-free piezoceramic 0.95(Na_0.5Bi_0.5)TiO₃-0.05BaTiO₃ (BNBT5) as the texture evolves from relatively sharp to a random distribution.

Figure 1. Modelled effect of axial texture on elastic compliance and piezoelectric charge constant of lead-free BNBT5 piezoceramic. As the width of the orientation distribution (Ω) increases, the elasticity tends to isotropic and the piezoelectricity collapses to zero.

[1] Villafuerte-Castrejón, M. E., Morán, E., Reyes-Montero, A., Vivar-Ocampo, R., Peña-Jiménez, J. A., Rea-López, S. O., & Pardo, L. (2016). Materials 9, 21. [2] Burciaga-Valencia, D. C., Villalobos-Portillo, E. E., Marín-Romero, J. A., Del Río, M. S., Montero-Cabrera, M. E., Fuentes-Cobas, L.E. & Fuentes-Montero, L. (2018). J. Mater. Sci: Mater. Electron. 29, 15376. [3] Villalobos-Portillo, E. E., Fuentes-Montero, L., Montero-Cabrera, M. E., Burciaga-Valencia, D. C. & Fuentes-Cobas, L. E. (2019). Mater. Res. Express 6, 115705. [4] Fuentes-Cobas, L. E., Chateigner, D., Fuentes-Montero, M. E., Pepponi, G & Grazulis, S. (2017). Adv. Appl. Ceram. 116, 428.

Sponsorship by the Consejo Nacional de Ciencia y Tecnología (México), Projects 257912 and 270738, is appreciated. Support from the Project MAT2017-86168-R“Piezocerámicas ecológicas para la generación de ultra-sonidos” (CSIC, Spain), is acknowledged.

Production of nanostructures of extended covalent systems has remained a long-standing challenge, mainly due to the elevated activation energies required for their crystallization.[1] Such solids tend to exhibit outstanding mechanical properties, i.e. superhardness, the most illustrative case being diamond. Moreover, if nanostructuration is achieved (ideally in the ≈10 nm size range), further enhancement of the hardness can be obtained. For instance, diamond nanorods show an increase of the hardness by 86% compared to the bulk (from 80 GPa to 150 GPa).[2] Superhard materials are of great industrial importance, with applications as cutting and polishing tools, coatings and abrasives. Diamond is indeed the traditional choice for such purposes, but it has well-known limitations: it is brittle, oxidizes to carbon dioxide at 800–900 °C in air and reacts with Fe‑containing solids during cutting, not to mention the difficulty and cost of its production associated to the high-pressure machinery needed.

While several possible diamond substitutes have been suggested, boron carbide (B_4+δC) stands as one of the few superhard phases that can be reached at room pressure. Boron carbide crystallizes in the R-3m spacegroup and its network is based on B icosahedra linked to each other through both direct B-B bond and CBC chains, as depicted in Figure 1. B_4+δC exhibits an intrinsic hardness of 38 GPa, yet far from the industrially profitable range. Plenty of effort has been devoted to the optimization of boron carbide’s particle size and consequent amelioration of its mechanical properties. Approaches using different reactants, lower temperatures (down to 600°C) and/or liquid-phase reactions have not been able to enable further lower the B_4+δC particle size. In this work, instead of using pristine reagents, we demonstrate the capacity to produce 10 nm B_4+δC nanoparticles from a nano-precursor, namely NaB₅C. The structure of this cubic compound (space group Fd-3c) resembles that of perovskites, where B₅C octahedra form an anionic network that leaves cavities filled by Na⁺ cations (Figure 1 left). 5-7 nm NaB₅C nanoparticles were synthesized by using a high temperature liquid-phase procedure in molten salts.[3] The intrinsic carbon and boron mixture in a composition lying well within the range of the B_4+δC solid solubility makes it an interesting precursor to yield boron carbide. Indeed, upon calcination, the NaB₅C nanostructures are transformed to B_4+δC with nanostructuration preservation at circa 10 nm. After hot-pressing densification, the synthesized powders show enhancement of their mechanical properties above any previous record. We have used powder X-ray diffraction to shed light on the transformation from NaB₅C to B_4+δC at the atomic level. The implications of the new morphology of B_4+δC on the mechanical properties will be discussed as well as the importance of the templating effect remaining from the original NaB₅C nanostructures.

In this presentation, I will highlight research opportunities and challenges in probing structural dynamics of molecular systems using X-ray Photon Correlation Spectroscopy (XPCS). The development of new X-ray sources, such as 4th generation storage rings and X-ray free-electron lasers (XFELs), provides promising new insights into molecular motion. Employing XPCS at these sources allows to capture a very broad range of timescales and lengthscales, spanning from femtoseconds to minutes and atomic scales to the mesoscale. Here, I will discuss the scientific questions that can be addressed with these novel tools for two prominent examples: the dynamics of supercooled water [1,2] and proteins [3]. Finally, I will provide practical tips for designing and estimating feasibility of XPCS experiments as well as on detecting and mitigating radiation damage.

[1] F. Perakis, K. Amann-Winkel, F. Lehmkühler, M. Sprung, D. Mariedahl, J. A. Sellberg, H. Pathak, A. Späh, F. Cavalca, D. Schlesinger, A. Ricci, A. Jain, B. Massani, F. Aubree, C. J. Benmore, T. Loerting, G. Grübel, L. G. M. Pettersson and A. Nilsson, Proc. Natl. Acad. Sci. U.S.A. 114, 8193-8198 (2017)
[2] F. Perakis, G. Camisasca, T. J. Lane, A. Späh, K. T.Wikfeldt, J. A. Sellberg, F. Lehmkühler, H. Pathak, K. H. Kim, K. Amann-Winkel, S. Schreck, S. Song, T. Sato, M. Sikorski, A. Eilert, T. McQueen, H. Ogasawara, D. Nordlund, W. Roseker, J. Koralek, S. Nelson, P. Hart, R. Alonso-Mori, Y. Feng, D. Zhu, A. Robert, G. Grübel, L. G. M. Pettersson, and A. Nilsson, Nature Comm. 9, 1917 (2018)
[3] F. Perakis and C. Gutt, Phys. Chem. Chem. Phys., 22, 19443-19453 (2020)

Additives provide a versatile strategy for controlling crystallization processes, enabling selection of properties including crystal sizes, morphologies, and structures. The additive species can also be incorporated within the crystal and even the crystal lattice itself, leading for example to enhanced mechanical properties. However, while many techniques are available for analysing particle shape and structure, it remains challenging to characterize the structural inhomogeneities and defects introduced into individual crystals by these additives, where these govern many important material properties. Here, we exploit coherent diffraction imaging methods to visualize the distribution of additives within as well as the effects additives have on the internal structure of individual calcite crystals. Highlighted are how factors including supersaturation, solution composition and additive-crystal interactions govern the distribution of additives in single crystals. Further, emphasized is the emergence of a range of complex strain and zonation patterns depending on the nature of the additive, diverging in part and locally from commonly suggested distribution models. This work contributes to our understanding of the factors that govern the structure-property relationships of crystalline materials, where a controlled utilization of additives will ultimately inform the design of next-generation materials.

Cateretê, the coherent X-ray scattering beamline at the new Brazilian synchrotron 5bent-achromat source, Sirius [1] is dedicated to coherent diffraction imaging (CDI) as well as X-ray photon correlation spectroscopy (XPCS) studies. Making the most of the coherence properties of the ultra-low emittance of the Sirius accelerator, will enable to perform 3D imaging of micrometer sized specimen down to few nanometers spatial resolution.

The Cateretê beamline is equipped with an undulator source, in a low-beta straight section, and two cryo-cooled focussing mirrors creating a 41 x 36 mm² (FWHM at 9 keV) coherent beam at 88 m from the source. The beamline operates in the 4 to 24 keV energy range using a horizontally deflecting 4-bounce crystal monochromator (4CM). Moving the 4CM laterally by a few mm, enables to operate the beamline in pink beam mode, maintaining the beam position unchanged. The experimental station is located 88 m from the source, followed by a 28 meters vacuum chamber hosting the Medipix (3k x 3k pixels²) in-vacuum detector.

The beamline, now under commissioning, will enable to perform imaging in reciprocal space, with a particular focus on in situ imaging as well as cryo-imaging experiments [2], [3]. To date, we measured and obtained the first three-dimensional reconstruction of a 6 microns cube zeolite crystal. XPCS studies of zeolite nucleation and growth have also been performed and will be presented.

An operando reaction cell, enabling to image catalysts under realistic catalytic conditions and a cryogenic sample environment are under development. The latter will allow 2D and tomographic data acquisition of specimens loaded in capillaries or flat substrates such as Si₃N₄membranes. The cryo-system is based on a low-flow cryo-cooled He gas preserving the sample stability and operates in a controlled humidity atmosphere preventing ice formation.

I will describe the Cateretê beamline and present the latest results obtained using plane-wave CDI as well as XPCS.

[1] L. Liu, N. Milas, A. H. C. Mukai, X. R. Resende, and F. H. De Sá, “The sirius project,” J. Synchrotron Radiat., vol. 21, no. 5, pp. 904–911, 2014.

[2] A. R. Passos et al., “Three-dimensional strain dynamics govern the hysteresis in heterogeneous catalysis,” Nat. Commun., vol. 11, no. 1, pp. 1–8, 2020.

[3] C. C. Polo et al., “Correlations between lignin content and structural robustness in plants revealed by X-ray ptychography,” Sci. Rep., vol. 10, no. 1, pp. 1–11, 2020.

Acknowledgements: MCTI, CNPq, Fapesp (2014/25964-5).

Topological defects are at the heart of many intriguing phenomena in fields as diverse as biology and materials science. Ability to manipulate the topological order at will has transformative implications for nanotechnology, particularly for next generation spintronic devices, solar cells, photonics, reconfigurable electronics, catalysts, and energy and information storage. To achieve such control, we must deepen our understanding of topological textures. It is therefore essential to comprehend their nature in 3D.
While electron microscopy methods achieve very high spatial resolution even in 3D, for this they rely on destructive slicing/milling techniques that (1) induce excessive strain on the samples, potentially significantly altering the energy landscape; and (2) render time-dependent studies impossible. On the other hand, X-rays have high penetration depth that allows them to access whole-volume information and are (mostly) non-destructive, preserving the structures under study. Moreover, X-rays do not interfere with electric and magnetic fields (as well as with visible light photons), allowing studies to be performed under external influences.
In this talk, we will show how Bragg coherent diffractive imaging, with help of Landau phase-field modelling, can be extended to the studies of ferroelectric domains, polar vortices [1] and 1D strings [2] in individual nanoparticles under external electric fields. Our results show that topological structures in ferroic materials can modulate the structural phase transition driven by electric field. When analyzing projections of toroidal moment, we also observed controllable chirality, which can be applied in next generation electronics. Tracking of the domain morphology and the vortex core lines suggests that some ferroic materials feature topological structures of the same universality class as hypothetical cosmic strings. This suggests that our methodology can be applied to the studies as exciting and fundamental as cosmology. We will further discuss how the same methodology can be adapted to the studies of large-scale topological textures in photonic networks imaged using ptychographic X-ray computed tomography [3]. We will emphasize the similarities between imaged topological entities and discuss implications of next generation synchrotron sources for the field.

[1] D. Karpov, Z. Liu, T. dos Santos Rolo, R. Harder, P. V. Balachandran, D. Xue, T. Lookman, and E. Fohtung, “Three-dimensional imaging of vortex structure in a ferroelectric nanoparticle driven by an electric field”, Nat. Comm. 8, 280 (2017)[2] D. Karpov, Z. Liu, A. Kumar, B. Kiefer, R. Harder, T. Lookman, and E. Fohtung, “Nanoscale topological defects and improper ferroelectric domains in multiferroic barium hexaferrite nanocrystals”, Phys. Rev. B 100, 054432 (2019)[3] High-resolution three-dimensional imaging of topological textures in gyroid networks (manuscript in preparation).

On one hand, coherent diffraction imaging (CDI) in Bragg geometry has emerged as a unique 3D microscopy of nanocrystals thanks to 3rd generation synchrotron sources. Away from absorption edges and at space-group allowed reflections, it provides not only the electronic density, but also, encoded in the phase, the atomic displacement field with respect to the mean lattice, which in turn reveals crystal strain, defects and domains [1–3]. On the other hand, some crystal structures have crystallographic reflections which are forbidden by the space-group symmetry but can nevertheless be observed at a suitable X-ray absorption edge, due to the anisotropy of the tensor of scattering (ATS) [4]. They are several orders of magnitude weaker than allowed reflections, but the absence of Thomson scattering allows the observation of various electronic phenomena related to electronic orders (magnetic, charge, orbital), static and dynamic atomic displacements.
The new generation of synchrotron sources, such as the ESRF “Extremely Bright Source”, opens opportunities to perform CDI on such weak reflections. Here we report on the measurement of the (115) forbidden reflection of a GaN nanopillar at the Ga K edge. Sufficient statistics could be obtained in a total accumulation time of ~30 minutes for an entire rocking curve to retrieve the phase of the scattering function. Such measurement at high temperature would provide an image of the inhomogeneity of thermal motion in the crystal [5], which would be particularly interesting close to surfaces, inversion domain boundaries [3] and crystal defects. This proof-of-principle experiment demonstrates that forbidden reflections are a new opportunity for CDI with the new synchrotron sources.

[1] Robinson, I. & Harder, R. (2009). Nature Materials 8, 291.
[2] Clarke, J., Ihli, J., Schenk, A. S., Kim, Y.-Y., Kulak, A. N., Campbell, J. M., Nisbet, G., Meldrum, F. C. & Robinson, I. K. (2015). Nature Materials 14, 780.
[3] Labat, S., Richard, M.-I., Dupraz, M., Gailhanou, M., Beutier, G., Verdier, M., Mastropietro, F., Cornelius, T. W., Schülli, T. U., Eymery, J. & Thomas, O. (2015). ACS Nano 9, 9210.
[4] Dmitrienko, V. E. (1983). Acta Cryst. A 39, 29.
[5] Beutier, G., Collins, S. P., Nisbet, G., Ovchinnikova, E. N. & Dmitrienko, V. E. (2012). Eur. Phys. J. Special Topics 208, 53.

The authors ackowledge the ESRF for beamtime allocation under project number MI-1377.

A solution to the crystallographic “phase problem” was proposed by David Sayre immediately after the announcement of Shannon’ Information Theorem, requiring the diffraction to be sampled more than twice as finely as the Bragg peak spacing [1]. The implicit need for X-ray coherence has been happily solved with the development of the latest synchrotron sources, where Bragg Coherent Diffraction Imaging (BCDI) experiments are routinely performed. The fringed diffraction patterns can be oversampled so as to overdetermine the phase problem. Iterative algorithms that converge on the solution. Despite meeting all the oversampling requirements of Sayre and Shannon, current iterative phase retrieval approaches still have trouble achieving a unique inversion of experimental data in the presence of noise. We propose to overcome this limitation by employing Machine Learning in a Convolutional Neural Network model which combines supervised training with unsupervised refinement. Remarkably, our model can be used without any prior training to learn the missing phases of an image based on minimization of an appropriate “loss function” alone. We demonstrate significantly improved performance with experimental Bragg CDI data over traditional iterative phase retrieval algorithms [1,2].

Cellulose is our most abundant biopolymer, and hence an important renewable raw material for many materials. Her, we present a small and wide angle X-ray scattering (SAXS/WAXS) study of regenerated cellulose textile fibers, air-gap spun from an ionic liquid solution.[1] Figure 1 shows SAXS and WAXS patterns from two fibers produced with two different draw ratios, DR=2 and 15, respectively. Drawing the fibers result in an increased degree of orientation of the crystalline domains (Figure 1c and d). By analyzing the azimuthal angular dependence of the WAXS pattern, both the crystal degree of orientation and the degree of orientation of amorphous cellulose chains can be obtained, as well as their relative contributions to the total scattering. Thus, offering an accurate determination of the degree of crystallinity. The anisotropic cross-like 2D SAXS pattern, having scattering predominantly perpendicular and parallel to the fiber axis, suggests an internal colloidal structure with oriented crystalline lamellae of ca. 10 nm thickness, embedded within a continuous matrix of amorphous cellulose. The lamellae are oriented with their normal parallel with the fiber axis.

[1] Gubitosi, M., Asaadi, S., Sixta, H., Olsson, U. (2021). Cellulose. 70, 3554

Structure determination of nano-size crystals is always a challenging problem. For quite lots of materials, it is very difficult to synthesize large/good enough crystals for single crystal X-ray diffraction studies. Powder X-ray diffraction (PXRD) is the major method for their atomic structure determination, PXRD is a quite mature technique and lots of powder structures were solved. However, for complicated structures with huge unit cell dimensions or those with crystal sizes smaller than 100nm, it is quite often to have severe peak overlapping problems, which makes it extremely difficult to solve the structure from PXRD alone. Electrons which interact with matter much stronger than X-ray can produce single-crystal-like diffraction from nano-crystalline materials, which makes it possible to collect single-crystal-like diffraction data.

The 3D electron diffraction technique can be used for collecting 3D electron diffraction data. Compared with traditional electron diffraction methods, this technique gives lower dynamical effects and much higher data completeness. Using the intensities abstracted from the data, complicated structures can be directly solved using the similar methods as single-crystal X-ray diffraction. Combining it with other techniques, such as PXRD or even SXRD, more complicated structures can be solved.

A strategy to enhance surface properties of nanocrystals is tailoring their bulk crystalline structure. As an example, the performance of metal nanocatalysts is correlated to lattice distortion induced by the mechanical anisotropy of the crystal structure [1]. We demonstrated that the stress caused by interior interfaces in core@shell nanocrystals results in larger lattice deformations than the elemental lattice mismatch [2]. Plasmonic applications push further the interest for a thorough characterization of the influence of the structural anisotropy on the thermal dynamic disorder.

Here we access the thermal disorder in Pd nanocrystals with molecular dynamics simulation. We focus on cubic nanocrystals, which have a particularly pronounced influence of mechanical anisotropy. We find a marked dependence of dynamic disorder on the crystallographic direction that enhances as crystal size decreases (see Fig. 1). 10 nm nanocrystals show a clear separation of the directional-dynamic disorder profiles. Contrary to theoretical models that ignore mechanical anisotropy, the directional profiles deviate from one another starting with the shortest pair distances.

We extracted an analytical model suitable for include the anisotropic thermal disorder we report here within existing analysis methods of both Bragg and PDF powder scattering profiles. Based on experimentally validated atomistic simulations, the model is calibrated with well-known characteristic material properties such as the bulk MSD and structural mechanical anisotropy (i.e., contrast factor). Finally, we used the whole pair distribution function modelling method [3] to test the model against the analysis of powder X-ray diffraction patterns simulated via Debye scattering equation.

Cadmium selenide nanocrystals (CdSe NCs) are frequently used in optoelectronic devices, as they possess unique optoelectronic properties that are highly sensitive to their size, shape and microstructure. Due to the high sensitivity of the properties to the microstructure features, the structure and microstructure of CdSe NCs must be controlled precisely during the synthesis. The CdSe NCs crystallize in thermodynamically stable wurtzitic structure (space group ), in metastable zinc blende structure (space group ) and in a mixture of both structures [1]. As a result, another critical issue of the CdSe NCs synthesis is the control of phase composition and formation of microstructural defects, as both issues affect the optoelectronic properties additionally [2,3].

The aim of this study was to correlate the size and morphology of CdSe NCs with their phase composition and with the formation of microstructure defects, and to explain the effect of the microstructure defects on the optoelectronic properties of the CdSe NCs. The CdSe NCs under study were produced using hot injection at temperatures between 225°C and 250°C. X-ray diffraction and transmission electron microscopy with high resolution revealed that the CdSe NCs have a size between 3 and 10 nm, and crystallize predominantly in the metastable zinc blende crystal structure. While NCs having a size smaller than 4 nm were practically defect-free, larger particles contained planar defects (stacking faults), which number increased with increasing NC size. When the planar defects appeared randomly in the interior of the NCs, then they led to an anisotropic broadening of the X-ray diffraction lines as typical for isolated stacking faults [4]. When the planar defects appeared on every second cubic lattice plane {111}, then they accomplished the transition of the zinc blende structure of CdSe to the thermodynamically stable wurtzitic modification [5]. A combination of XRD measurements and simulations using DIFFaX revealed that the interplanar spacing along the stacking direction apparently depends on the density and ordering of the planar defects. Our approach is discussed together with the approach of Moscheni et al. [6].

In general, the planar defects located in the interior of the CdSe NCs deteriorate their photoluminescence quantum yield. Additional planar defects originate from the oriented attachment of CdSe NCs along the {111} crystallographic planes. These defects disturb the crystallographic coherence of attached NCs. Consequently, agglomerated NCs are not recognized as large NCs but as separated NCs both by XRD and by photoluminescence.

[1] Bawendi, M. G., Kortan, A. R., Steigerwald, M. L. & Brus, L. E. (1989). J. Chem. Phys. 91, 7282.

[2] Viswanatha, R. & Sarma, D. D. (2009). Chem.: Asian J. 4, 904.

[3] Orfield, N. J., McBride, J. R., Keene, J. D., Davis, L. M. & Rosenthal, S. J. (2015). ACS Nano 9, 831.

[4] Warren, B. E. (1990). X-ray Diffraction. New York: Dover Publication.

[5] Martin, S., Ullrich, C., Šimek, D., Martin, U. & Rafaja, D. (2011). J. Appl. Cryst. 44, 779.

[6] Moscheni, D., Bertolotti, F., Piveteau, L., Protesescu, L., Dirin, D. N., Kovalenko, M. V., Cervellino, A., Pedersen, S., Masciocchi, N. A. & Guagliardi, A. (2018). ACS Nano 12, 12558.

Understanding and governing the complex behavior in magnetic materials at the nanoscale is the key and the challenge not only for fundamental research but also to exploit them in applications ranging from catalysis,[1] to data storage,[2] sorption,[3-4] biomedicine,[5-6] and environmental remediation.[7] In this context, spinel ferrites (M²⁺Fe²O⁴, where M²⁺ = Fe, Co, Mn, etc.) represent ideal magnetic materials for tuning the magnetic properties through chemical manipulations, due to their strong dependence on the cation distribution, spin-canting, interface, size, shape, and interactions. Furthermore, when coupled with other phases (heterostructures), they can display rich and novel physical properties different from the original counterparts (exchange coupling, exchange bias, giant magneto-resistance), allowing them to multiply their potential use.[8] For example, the possibility to tune magnetic anisotropy and saturation magnetization by coupling magnetically hard and soft materials have found usage recently in applications based on magnetic heat induction, such as catalysis or magnetic fluid hyperthermia (MFH).[9] Therefore, it is crucial to engineer core-shell nanoparticles with homogeneous coating and low size dispersity for uniform magnetic response and to maximize the coupling between the hard and soft phases (i.e. the interface).[10] Even though some studies have reported interesting results in the field of magnetic heat induction, a systematic study on an appropriate number of samples for a better comprehension of the phenomena to optimize the performance is needed.

In this contribution, the capability of coupled hard-soft bi-ferrimagnetic nanoparticles to improve the heating ability is exploited to understand the influence of the different features on the performances. This systematic study is then based on the correlation between the heating abilities of three magnetically hard cobalt ferrite cores, covered with magnetically soft spinel iron oxide and manganese ferrite having different thickness, with their composition, structure, morphology and magnetic properties. Direct proof of the core-shell structure formation was provided by nanoscale chemical mapping, with identical results obtained through STEM-EELS, STEM-EDX, and STEM-EDX tomography. ⁵⁷Fe Mössbauer spectroscopy and DC/AC magnetometry proved the magnetic coupling between the hard and the soft phases, thanks also to the comparison among core-shell NPs, ad-hoc prepared mixed cobalt-manganese ferrites NPs, and cobalt ferrite NPs mechanically mixed with manganese ferrite NPs. The heating abilities of the aqueous colloidal dispersions of the three sets of core-shell samples revealed that, in all cases, core-shell nanoparticles showed better performances in comparison with the respective cores, with particular emphasis on the spinel iron oxide coated systems and the samples featuring thicker shells. This scenario entirely agrees with the hypothesis made based on magnetic parameters (saturation magnetization, Néel relaxation times, effective anisotropy) of the powdered samples, and demonstrated the importance of a sophisticated approach based on the synergy of chemical, structural, and magnetic probes down to a single-particle level.

[1] Polshettiwar, V. et al. Chem. Rev., 2011, 111, 3036–3075

[2] Wu, L. et al. Nano Lett., 2014, 14, 3395–3399

[3] Cara, C. et al. J. Mater. Chem. A, 2017, 5, 21688–21698

[4] Cara, C. et al. J. Phys. Chem. C, 2018, 122, 12231–12242

[5] Lim, E. et al. Chem. Rev., 2015. 115, 327-394

[6] Mameli, V. et al. Nanoscale, 2016, 8, 10124–10137

[7] Westerhoff, P. et al. Environ. Sci. Nano, 2016, 3, 1241–1253

[8] Gawande, M.B. et al. Chem. Soc. Rev. 2015, 44, 7540–7590

[9] Lee, J.-H. et al. Nat. Nanotechnol.,2011, 6, 418–422

[10]Sanna Angotzi, M. et al. J. Nanosci. Nanotechnol., 2019, 19, 4954–4963

Lead bromide perovskite nanocrystals (NCs) APbBr₃ in which A: Cs, FA: CH(NH₂)₂, MA: CH₃NH₃ are very promising high-color purity light emitters due to their pure green emission and excellent optical properties. In this present work, the lead bromide perovskite APbBr₃ (A: Cs, FA, MA)nanocrystals have been synthesized by the hot injection method according to. Imran et al ¹ synthesis approach in which the benzoyl bromide was used as halide precursor which can be easily injected into a solution of metal cations to provoke the nucleation and the growth of Lead bromide perovskite NCs. By precisely tuning the relative amount of cation precursors (cesium carbonate and lead acetate for Cs perovskite, formamidine acetate and lead acetate for FA perovskite, and methylamine and lead oxide for MA perovskite), ligands (oleylamine and oleic acid), solvents (octadecene), benzoyl bromide, and the injection temperature (170°C Cs perovskite, 75°C for FA perovskite, 65 °C for MA perovskite), we have been able to synthesize inorganic and organic-inorganic lead bromide perovskite APbBr₃ colloidal nanocubes with excellent control over the size distribution, very high phase purity, and excellent optical properties such as a high green photoluminescence emission efficiency and narrow full width at half-maximum. The resultant lead bromide perovskite nanocrystals (NCs) APbBr₃ present important optical properties, which are among the best-promoting characteristics for a pure green light-emitting device according to the updated recommendation 2020 (Rec. 2020) standard ².

References:

1: Imran, Muhammad, et al. "Benzoyl halides as alternative precursors for the colloidal synthesis of lead-based halide perovskite nanocrystals." Journal of the American Chemical Society 140.7 (2018): 2656-2664.

2: Zhu, Ruidong, et al. "Realizing Rec. 2020 color gamut with quantum dot displays." Optics express 23.18 (2015): 23680-23693.

Most nanocrystals are expected to show deviations from a perfect crystal lattice inside the grains, which is referred to as modulation waves[1], because of their significant surface effects, leading to exceptional physical and chemical properties. Conventional X-ray diffraction fails to reveal modulation waves owing to the assumption of the periodic structure, whereas electron diffraction from a single grain is one of the most powerful probes to distinguish the core structure from the surface structure on the atomic level. It is, however, still challenging to investigate modulation waves from the core to the surface, which is the atomic-level core-shell structure. In this study, we have demonstrated that synchrotron X-ray total scattering makes it possible to visualize the core-shell structure on the picometer level in Pd nanocrystals.

X-ray total scattering provides a potential for visualization of modulation waves[2]; nevertheless its applications have been very limited because the approach is extremely demanding of experimental data. We have developed the high-resolution and high-accuracy total scattering measurement system, OHGI (Overlapped High-Grade Intelligencer), at SPring-8[3,4] to overcome the limitations. Recent studies have demonstrated that our total scattering data are of the highest quality in terms of both Bragg and diffuse scattering[5-7]. With this system, Pd nanocrystals were measured under hydrogen pressure. The total scattering data were converted into atomic pair distribution functions (PDF) on the basis of the principle of maximum entropy[8]. The resulting PDFs were virtually free from spurious ripples at no expense of real-space resolution. We have attempted to model modulation waves from the PDFs on the basis of an fcc Pd lattice. The model suggests that the interatomic distances between Pd atoms in the shell region are longer than those in the core by a few picometers. In addition, we found that the core-shell structure undergoes significant changes by hydrogenation. The picometer-level core-shell structure can explain that implied by neutron diffraction, where both tetrahedral and octahedral sites are occupied by hydrogen atoms in the surface[9]. In this presentation, I will discuss the relationship between the modified core-shell structure and hydrogen-storage kinetics in Pd nanocrystals.

[1] Hudry, D., Howard, I. A., Popescu, R., Gerthsen, D. & Richards, B. S. (2019). Adv. Mater. 31, 1900623.

[2] Palosz, B., Grzanka, E., Gierlotka, S. & Stelmakh, S. (2010). Z. Kristallogr. 225, 588.

[3] Kato, K., Tanaka, Y., Yamauchi, M., Ohara, K. & Hatsui, T. (2019). J. Synchrotron Rad. 26, 762.

[4] Kato, K. & Shigeta, K. (2020). J. Synchrotron Rad. 27, 1172.

[5] Svane, B., Tolborg, K., Kato, K. & Iversen, B. B. (2021). Acta Cryst. A77, 85.

[6] Pinkerton, A. (2021). Acta Cryst. A77, 83.

[7] Beyer, J., Kato, K. & Iversen, B. B. (2021). IUCrJ 8, 387.

[8] Kato, K. et al., submitted.

[9] Akiba, H., Kofu, M., Kobayashi, H., Kitagawa, H., Ikeda, K., Otomo, T. & Yamamuro, O. (2016). J. Am. Chem. Soc. 138, 10238.

Permanent magnets are key enablers driving the 21^st century’s diverse electromagnetic technologies [1]. Ceramic magnets based on iron oxides are corrosion resistant and cost-effective permanent magnetic materials with minimal ecological footprint, compared to their lanthanide-based counterparts (such as SmCo₅; Nd₂Fe₁₄B etc.) [1,2]. Among the ceramic magnets, the hexaferrites (AFe₁₂O₁₉; A = Ba/Sr) constitute the bulk of industrially produced permanent magnets [3,4]. A permanent magnet’s properties emerge hierarchically and are influenced by the structure on various length scales. From atomic interactions in the unit cell (~ 1–10 Å), through the interactions between crystallites/domains (~10 nm–1 µm), to the consolidated macroscopic forms (~ 0.1 mm–0.1 m), magnetism evolves over length scales spanning 10 orders of magnitude [5]! For maximal magnetic performance, the structure of a permanent magnet must be optimized at all levels. Control over the structure is obtained by controlling the synthesis and processing parameters. Additionally, these fabrication methods need to be economical, effective and compatible with industrial scale synthesis processes.

Recent work from our group has demonstrated the fabrication of high-performance nanostructured SrFe₁₂O₁₉ hexaferrite permanent magnets from solid-state processing of ferrihydrite – a poorly crystalline, structurally disordered nanomaterial [6,7]. This fabrication method is low-cost, scalable and compatible with industry processes. In the presence of Sr²⁺ ions, ferrihydrite is seen to act as a building block for the SrFe₁₂O₁₉ hexaferrite, irrespective of synthesis technique (hydrothermal/microwave/solid-state synthesis) [7–9]. While the transformation of ferrihydrite to hexaferrite has been documented in previous studies, a detailed understanding of the conversion process in situ is lacking. The fundamental question that remains to be answered: how does long-range crystalline order in the hexaferrite magnet arise from the nanoscale-disordered ferrihydrite precursor?

Here, we report on our efforts towards addressing this question using in­ situ­ synchrotron X-ray scattering studies to investigate the ferrihydrite-hexaferrite transformation. Ferrihydrite samples (with Sr²⁺) were heated while scattering data was collected in situ at the P02.1 beamline at PETRA III. The P02.1 beamline allows for 2 operating modes separately optimized for X-ray Bragg scattering and total scattering[10]. In situ X-ray scattering experiments were performed in both modes. Combining Rietveld modelling of Bragg scattering data and Pair Distribution Function (PDF) modelling of total scattering data provided detailed insight into the real-time structural evolution of disordered ferrihydrite to crystalline hexaferrite. PDF analysis shed light on the evolution of the short- and intermediate-range structural features during the transformation. Rietveld analysis helped ascertain the long-range order, nanoscale morphology and crystallite growth mechanism. This clear picture of the ferrihydrite-hexaferrite transformation over multiple relevant length scales is expected to aid future efforts in engineering better permanent magnets. Meanwhile, beyond permanent magnetic materials, these insights are also expected to contribute toward a broader understanding of the evolution of crystalline order from nanoscale disorder.

[1] Gutfleisch, O., Willard, M. A., Brück, E., Chen, C. H., Sankar, S. G., & Liu, J. P. (2011) Adv. Mater. 23, 821.

[2] Sugimoto, M. (2010) J. Am. Ceram. Soc. 82, 269.

[3] Pullar, R. C. (2012) Prog. Mater. Sci. 57, 1191.

[4] de Julian Fernandez, C., Sangregorio, C., de la Figuera, J., Belec, B., Makovec, D., & Quesada, A. (2020) J. Phys. D. Appl. Phys. 54, 153001.

[5] Skomski, R. (2003) J. Phys. Condens. Matter. 15, R841.

[6] Christensen, M. & Vijayan, H. Enhanced magnetic properties through alignment of non-magnetic constituents (2020) European Provisional Patent P5698EP00-CLI 2020.

[7] Vijayan, H., Knudsen, C. G., Mørch, M. I., & Christensen, M. (2021) Mater. Chem. Front. 5, 3699.

[8] Granados-Miralles, C., Saura-Múzquiz, M., Bøjesen, E. D., Jensen, K. M. Ø., Andersen, H. L., & Christensen, M. (2016) J. Mater. Chem. C. 4, 10903.

[9] Grindi, B., BenAli, A., Magen, C., & Viau, G. (2018) J. Solid State Chem. 264, 124.

[10] Dippel, A.-C., Liermann, H.-P., Delitz, J. T., Walter, P., Schulte-Schrepping, H., Seeck, O. H., et al. (2015) J. Synchrotron Radiat. 22, 675.

While simple associations exist between piezoelectric properties and processing history, there is considerable scope for design of materials based on a more detailed molecular understanding of the re-arrangements which underpin the piezoelectric phenomenon in silk fibroin.[1] Crystallinity, and the two-phase model of semi-crystalline model of polymers, are often used to understand the properties of protein based materials where there is considerable thermodynamic drive to short range ordering of polymer chains, folding, which is not present in melt processed thermoplastics. Our investigations aim to probe the relationship between structure and dynamics in silk fibroin based materials and correlate these with the piezo-electric signal.

Recently, we have used a triggered and summative data acquisition scheme to synchronise of X-ray scattering data with a piezoelectric cycle of a compressed electro-spun fibroin mat.[2] This mode, provided a steady perturbed state can be sampled, the summation of multiple similar stages to provide superior statistics than would be possible by sampling a single cycle. The setup is shown in Figure 1A. At rest this poorly ordered system exhibits a limited number of very broad peaks but quite a high degree of chain folding.[3] With compression there is marked increase in the scattered intensity, both in the small (SAXS) and the wide (WAXS) angle regimes, as well a shift and reduction in broadness of the WAXS peaks (Figure 1B). We interpret the increase in the SAXS signal as an increase in scattering from grain boundaries and the WAXS as the formation of new crystalline domains. However, the limited number of very broad diffraction peaks make these data unsuitable for structural determination.

In order to provide an alternative, but complementary, perspective on the structural dynamics and the nature of the potential surface along which the polymer folds, during the piezo cycle we have turned to a computation approach. Density functional theory (DFT) calculations were performed within the framework of the projector augmented wave potentials parametrised by Perdew et al., [3] and the Tkatchenko-Scheffler correction [4] with a self-consistent screening to account for the weak correlations. Full structural optimisation of orthorhombic C₂₀O₈N₈H₃₂ was performed. The calculated lattice parameters (a = 9.409 Å, b = 6.984 Å, c = 9.221 Å) and the corresponding diffraction pattern (black vertical lines) are compared with the experimental data in Figure 1C.

Keywords: piezoelectricity; biopolymer; synchrotron wide angle X-ray scattering; millisecond resolved diffraction

The authors acknowledge beamtime on the SAXS/WAXS beamline at the Australian Synchrotron, part of ANSTO. The computations were performed on resources provided by the Swedish National Infrastructure for Computing (SNIC) at National Supercomputer Centre (NSC) in Linköping, Sweden.

[1] Rockwood, D. N., Preda, R. C., Yücel, T., Wang, X., Lovett, M. L. & Kaplan, D. L. (2011). Nature Protocols 6, 1612.

[2] Sencadas, V., Garvey, C., Mudie, S., Kirkensgaard, J. J. K., Gouadec, G. & Hauser, S. (2019). Nano Energy 66, 104106.

[3] Perdew, J. P., Burke, K. & Ernzerhof, M. (1996). Physical Review Letters 77, 3865-3868.

[4] Tkatchenko, A. & Scheffler, M. (2009). Physical Review Letters 102, 073005.

High-throughput synthesis using inkjet printing allows the deposition of hundreds of nanoparticle compositions on a single substrate. It also introduces the challenge to characterize the phases and structures of these nanoparticles in an automated high-throughput way. Here, we develop a method to screen hundreds of nanoparticle combinations, collect the x-ray diffraction image, transfer the data to pair distribution functions and analyze the phase information. It has been successfully applied to characterize the phase compositions and atomic structures in an iron, nickel, cobalt nanoparticle array. Combining this method with inkjet printing and optical screening, it is possible to achieve the fully automated high-throughput searching for the optimal combinatorial nanoparticle catalysts.

Functional nanomaterials are frequently synthesized by the facile sol-gel method. In a broader sense, the process can be described as the conversion of molecular precursors in solution into inorganic solids via hydrolysis, condensation and aggregation [1]. It allows the targeted control of structural characteristics e.g. particle/crystallite size and polymorphism of a material. This is of particular importance for quantum materials, where the charge, spin, orbital and lattice are intrinsically coupled due to strong electronic interactions [1]. Since the sol-gel method is a non-equlibrium process, the synthesis of pure nanocrystalline samples is challenging if various stable and metastable phases exist, often leading to co-crystallization. Subtle changes in the synthesis parameters, such as temperature, pH and complexing agent, can strongly influence the resulting structural and physical properties of the materials. Despite this knowledge and the popularity of this synthesis method, studies on the parameters driving the crystallization process are rare and a deep understanding of the formation mechanisms is usually lacking.

The Bi₂O₃-Fe₂O₃ system is known to be challenging from a synthetic point of view, as sillenite-type Bi₂₅FeO₃₉, mullite-type Bi₂Fe₄O₉ and perovskite-type BiFeO₃ have a strong tendency to co-crystallize [3]. The target compound Bi₂Fe₄O₉ shows multiferroic behaviour close to room-temperature [4] and a spin liquid state just above the transition [5]. Its exotic magnetism materialises due to five competing magnetic exchange interactions involving two distinct Fe-sites, which drive antiferromagnetic coupling in the ab–plane and non-collinear ferromagnetic ordering along the c-axis [6]. Below a critical size of ~120 nm, size-dependent properties can be observed due to significant changes in the structural lattice [7].

In this study, we investigate how the synthesis parameters in a sol-gel approach affect the crystallization pathways and kinetics of Bi₂Fe₄O₉. We follow the transformation of molecular precursors into the fully crystalline structures using in situ total scattering and Pair Distribution Function (PDF) analysis with a second-scale time resolution. In total, five different precursors were synthesized using the respective metal nitrates and meso-erythritol as the complexing agent. The phases qualitatively appearing during crystallization as well as their transition and growth kinetics can be controlled by the synthesis medium and ratio of metal nitrate to complexing agent. More specifically, we observe multiple crystallization pathways including the initial formation of rhombohedral BiFeO₃ and subsequent transition into orthorhombic Bi₂Fe₄O₉, co-crystallization of BiFeO₃ and Bi₂Fe₄O₉, or the direct formation of Bi₂Fe₄O₉ from the precursor. During crystal growth, the lattice parameter b decreases significantly, although Bi₂Fe₄O₉ is known to exhibit positive thermal expansion [8] highlighting the influence of the crystallite size on the lattice. In addition, the overall crystallization process is predetermined very early in the synthesis process and mainly governed by the gel structures formed during evaporation of the solvent and organic components, as suggested by ex situ PDF analysis.

[1] Niederberger, M. (2007). Acc. Chem. Res. 40, 793. [2] Samarth, N. (2017). Nat. Mater. 16, 1068.

[3] Carvalho, T. T. & Tavares, P.B. (2008). Mater. Lett. 62, 3984.

[4] Singh, A. K., Kaushik, S. D, Kumar, B., Mishra, P. K., Venimadhav, A., Siruguri, V. & Patnaik, S. (2008). Appl. Phys. Lett. 92, 132910.

[5] Beauvois, K., Simonet, V., Petit, S., Robert, J., Bourdarot, F., Gospodinov, M., Mukhin, A. A., Ballou, R., Skumryev, V. & Ressouche, E. (2020). Phys. Rev. Lett. 124, 127202.

[6] Ressouche, E., Simonet, V., Canals, B., Gospodinov, M. & Skumryev, V. (2009). Phys. Rev. Lett. 103, 267204.

[7] Kirsch, A., Murshed, M. M., Litterst, F. J. & Gesing, Th. M.(2019). J. Phys. Chem. C 123, 3161.

[8] Murshed, M. M., Nénert, G., Burianek, M., Robben, L., Mühlberg, M., Schneider, H., Fischer, R. X. & Gesing, Th. M. (2013). J. Solid State Chem. 197, 370.

Keywords: Crystallization; Pair Distribution Function analysis; Phase transition; In situ total scattering; X-ray diffraction; Synthesis

“Funded by the Deutsche Forschungsgemeinschaft (DFG – German Research Foundation), project number 429360100”

The local structures of four citric acid cross linked cyclodextrin nanosponges (CD); goethite (CDG), hydroxyapatite (CDHA) and goethite/hydroxyapatite (CDGHA) functionalized cyclodextrin nanosponges, prepared by ultrasound-assisted polycondensation polymerization, was studied the using atomic pair distribution function (PDF) technique. The PDFs were analyzed by comparing experimentally determined PDFs from samples under study and those from known control samples and the overall structural information extracted through visual inspections of PDFs. The samples do show the feature of cyclodextrin network linked by citric acid, with strong sharp peaks in the low-r region and weak broader peaks in the mediate and high-r region. CD and CDHA show the feature of polymer cyclodextrin, since there is only noise and density modulation after 13 Å in their PDFs, while the CDG and CDGHA show the feature of crystallinity (signal even after 13 Å), which is approximately the largest atomic distance in cyclodextrin. The short-range order, which is the spacing of neighbor glucose and glucose connected by citric acid networks, is similar for all samples despite their difference in crystallization. CD and CDHA have quite similar cyclodextrin network according to their similarity in PDF while CDG and CDGHA also have cyclodextrin network but contains crystalline goethite.

See separate file

X-ray absorption spectroscopy (XAS) has imposed as a powerful method to track structural and chemical dynamics of metal ions hosted in nanoporous frameworks, such as zeolites and metal-organic frameworks (MOFs), for selective redox catalysis applications [1]. Analysis of the XANES and EXAFS regions offers a highly complementary view with respect to diffraction-based methods guaranteeing a unique sensitivity to the local electronic and structural properties of metal centers. These are often disorderly distributed in the crystalline matrix, and occur as dynamic mixtures of different species, responding to the physico-chemical environment while undergoing a rich redox chemistry mediated by host-guest interactions. Continuous instrumental developments at synchrotron sources today enable in situ/operando XAS studies at high time and energy resolution, allowing to monitor such dynamic systems with unprecedented accuracy [1]. In this contribution, the potential of these methods, empowered by advanced data analysis strategies and synergic integration with multi-technique laboratory characterization and computational modelling, will be exemplified by selected research results.

A first example will focus on the Cu-exchanged chabazite (Cu-CHA) zeolite, currently representing the catalyst of choice for deNO_x applications in the automotive sector via NH₃-assisted Selective Catalytic Reduction [2]. Here, the potential of Multivariate Curve Resolution (MCR) of time-resolved XANES datasets, quasi-simultaneous XANES/PXRD, and EXAFS Wavelet Transform analysis will be highlighted, to accurately quantify condition/composition-dependent Cu-speciation in CHA zeolites and therein establish robust structure-activity relationships, essential to design improved catalysts. A second case study will consider local structural and chemical transformations of Pt ions in Pt-functionalized UiO-67 MOFs [3], tracked by parametric refinement of time-resolved operando EXAFS under conditions yielding either isolated Pt^II sites anchored to the MOF framework (potentially interesting for C−H bond activation) or very small Pt⁰ nanoparticles inside the MOF cavities (potentially interesting for hydrogenation reactions).

[1] S. Bordiga et al., Chem. Rev. 2013, 113, 1736. C. Garino et al., Coord. Chem. Rev. 2014, 277-278, 130. E. Borfecchia et al., Chem. Soc. Rev. 2018, 47, 8097.

[2] A. Martini et al, Chem. Sci. 2017, 8, 6836. C. W. Andersen, et al., Angew. Chem. Int. Edit. 2017, 56, 10367. K. A. Lomachenko et al., J. Am. Chem. Soc. 2016, 138, 12025. C. Negri et al., J. Am. Chem. Soc. 2020, 142, 15884.

[3] S. Øien, et al., Chem. Mater. 2015, 27, 1042. L. Braglia, et al., Phys. Chem. Chem. Phys. 2017, 19, 27489. L. Braglia, et al., Faraday Discuss. 2017, 201, 265.

This investigation is devoted to metal-organic frameworks (MOFs) with UiO-67 topology, the materials with a three-dimensional porous structure and high surface area. Due to the diversity of species, MOFs are used in such areas as luminescent sensors, catalysts, filters, storage and transportation of light gases, and many others [1]. Using noble metals to functionalize metal-organic frameworks is a promising way for constructing new materials for catalytic applications [2, 3]. Although numerous successful synthesis of MOFs functionalized by metal ions and metal nanoparticles were reported, the exact mechanisms of structural evolution of the metal sites in many cases are still unknown. Determination of these mechanisms as well as investigation of the intermediate active sites formed during the synthesis is important for tailoring the specific catalytic properties of materials. In this work, we investigate structural changes in UiO-67 functionalized by Pd and Pt depending on the activation conditions by a combination of theoretical and experimental techniques.

Functionalization of UiO-67 by Pd and Pt was achieved via substitution of 10% standard biphenyl dicarboxylate linkers by MCl₂-2,2-bipyridine-5,5-dicarboxylic acid (MCl₂bpydc, M = Pd, Pt) [4, 5]. The obtained materials were further activated by heating to 300 °С in inert (He) and reducing (H₂/He) atmospheres. Evolution of the atomic and electronic structure was monitored by in situ extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) spectroscopies and X-ray powder diffraction (XRPD). All spectroscopic data for Pd K- and Pt L₃-edges were analysed simultaneously by MCR-ALS approach [6] to determine the number of pure species formed during the activation and their spectra.

To interpret the experimental data, we have performed DFT-calculations and XANES simulation by FDMNES code for different potential intermediates. The atomic models included the initial MCl₂bpydc linker and a number of possible reaction pathways in presence of H₂ substitution of both chlorine atoms by hydrogen atoms with formation of Cl₂ molecule, substitution of one chlorine by hydrogen atom with formation of HCl molecule; detachment of one or two chlorines with formation of HCl molecules, detachment of MCl₂ fragment from the linker with its substitution by two hydrogens bonded to nitrogen atoms of the linker; and simulating inert conditions: simple detachment of MCl₂ fragment, detachment of chlorines with formation of Cl₂ molecule. All reaction pathways were ranged according to the calculated reaction enthalpies and XANES spectra were calculated for the most probable ones.

The reaction pathways with the lowest reaction enthalpies were verified by good agreement between calculated and experimentally observed XANES spectra. For UiO-67-Pd, detachment of PdCl₂ is the most probable pathway in both inert and H₂ atmospheres which correlate with experimental results. For UiO-67-Pt, four different structures have been identified. In the presence of hydrogen, detachment of one chlorine atom should occur first. The second possible transition in the same environment is the detachment of PtCl₂ from the linker with the addition of two hydrogen atoms to nitrogen atoms with the further formation of Pt nanoparticles at temperatures above 200 °C. While formation of bare Pt-sites occurs from 200 to 300 °C in the inert flow [7, 8]. Thus, the XANES spectroscopy supported by theoretical calculations allowed verifying and describing intermediate states from the experimental spectra.

[1] Evans J. D., et al., Coord Chem Rev. (2019) 380 378-418. [2] Tanabe K. K., Cohen S. M., Chem Soc Rev. (2011) 40 (2) 498-519. [3] Wang Z., Cohen S. M., Chem Soc Rev. (2009) 38 (5) 1315-29. [4] Braglia L., et al., Phys Chem Chem Phys. (2017) 19 (40) 27489-27507. [5] Bugaev A. L., et al., Faraday Discuss. (2018) 208 287-306. [6] Jaumot J., et al., Chemom Intell Lab Syst. 140 (2015) 1-12. [7] Bugaev A. L., Skorynina A.A., et al., Catal. Today. (2019), 336, 33-39. [8] Bugaev A. L., Skorynina A.A., et al., Data Brief. (2019) 25, 104208.

Keywords: XANES; XRD; MOFs; MCR; DFT

This research was supported by the Russian Science Foundation, project № 20-43-01015.

Many catalysts for energy related applications, in particular metallic nanoalloys, readily undergo atomic-level changes during the electrochemical reactions driving the applications. The origin, dynamics and impact of the changes on the performance of the catalysts under actual operating conditions are, however, not well understood. This is largely because they are studied on model nanocatalysts under controlled laboratory conditions. We will present results from recent studies [1, 2, 3] on the dynamic behavior of metallic nanoalloy catalysts inside an operating proton exchange membrane fuel cell. Results show that their atomic structure changes profoundly, from the initial state to the active form and further along the cell operation. The electrocatalytic activity of the nanoalloys also changes. The rate and magnitude of the changes may be rationalized when the limits of traditional relationships used to connect the composition and structure of nanoalloys with their electrocatalytic activity and stability, such as Vegard’s law, are recognized. In particular, deviations from the law can well explain the behaviour for Pt-3d metal nanoalloy catalysts under operating conditions. Moreover, it appears that factors behind their remarkable electrocatalytic activity, such as the large surface to volume ratio and “misfit” between the size of constituent atoms, are indeed detrimental to their stability inside fuel cells. The new insight into the atomic-level evolution of nanoalloy electrocatalysts during their usage is likely to inspire new efforts to stabilize transient structure states beneficial to their activity and stability under operating conditions, if not synthesize them directly.

1. V. Petkov et al. Nanoscale 11, 5512 (2019).
2. Zh. Kong et al. J. Am. Chem. Soc. 142, 1287 (2020).
3. Z.-P. Wu et al. Nature Commun. 12, 8597 (2021)

The topic of renewable energies is vastly received as an x-factor towards our energy problems in this modern world times. This notion holds tight following the current global outcry of dilapidating fossil fuels. The science fraternity continually aims at tabling innovative strategies towards engineering renewable energy sources. This transcends to efforts of making chemical fuels which are easily storable using solar energy.

Water reduction catalysts (WRCs), as widely known, are currently used for the splitting of water to H₂ and O₂. The hydrogen (H₂) generated, is eyed as a prominent potential fuel source. These catalysts are often tailored with different transition metal elements somewhat coupled with effective macro-cyclic organic scaffolds [1]; as suitable approach to store energy at times of reduced power supply by harnessing solar energy [2,3].This renowned WRC science was preceded by the prominent scientific stun of the ruthenium(III) complex {[Ru^III(byp)₃]³⁺}, as a photo-synthesizer [4]. Interestingly, different other light harvesting moieties are lately being considered, exhibiting greater photo-stability, longevity and rigidity as elemental prerequisites [5], many of whom are based on polypyridyl entities.

In this presentation we discuss aspects of the ligand design strategy and cobalt coordination chemistry as exhibited in the value chain in the scheme just above. X-ray crystallographically characterised structures will be used to discuss different relative geometric preferences and characteristics of the respective analogues.

Alternative fuel sources are needed to replace fossil fuels to reduce the emission of greenhouse gases contributing to global warming. Hydrogen gas is one popular choice to replace fossil fuels [1] as an energy storage medium, due to its high energy density per unit weight. Hydrogen can be generated renewably by sunlight driven, photocatalytic water-splitting. Metal oxides, including those with a Ruddlesden-Popper layered perovskite structures are being studied as potential photocatalysts [2]. The structure contains multiple cationic sites, which allows for different combinations of metal cations for tuning the bandgap. The layered structuring also allows for the intercalation of different cations within the structure that allows for modifications post synthesis, therefore further optimising the photocatalyst [3].

KLaTiO₄ is a n=1 Ruddlesden-Popper that can be used as a Hydrogen Evolution Catalyst (HEC), producing 9.540 μmol of H₂ gas per hour from 20 mg of catalyst, when using methanol as sacrificial electron donor and platinum co-catalyst, and illuminated by a Hg lamp with a 305 nm cut-off filter. The main disadvantage of KLaTiO₄ is its high bandgap (4.09 eV) that is above the visible light region, which makes it a poor choice for a HEC that uses solar energy. Reduction of the bandgap of KLaTiO₄ for sunlight driven hydrogen evolution was attempted by cationic and anionic doping. The crystal structures, and sample purity, was determined using synchrotron X-ray powder diffraction (PXRD) and Rietveld refinement.

Cationic doping of KLaTiO4 was achieved by partially replacing lanthanum with praseodymium or ytterbium, yielding two solid solution series: KLa_xPr_1-xTiO₄ and KLa_xYb_1-xTiO₄ (x = 0.005, 0.01 and 0.03). While none of the samples from KLa_xPr_1-xTiO4 series produced hydrogen, all the KLa_xYb_1-xTiO₄ were able to produce H₂. In comparison to KLaTiO4, ytterbium-doped samples have reduced catalytic activity compared to KLaTiO₄, as seen in figure 1.

Anionic doping of KLaTiO₄ was attempted with nitrogen. Attempts to synthesise KLaTiO₃N were done by using TiN as a reagent in place of TiO2 with annealing the sample under N₂ flow at 800 °C. PXRD patterns of initial samples show good crystallinity, and no observable structural difference to KLaTiO₄. When tested as HEC in identical testing condition stated above all nitrogenated samples had similar rates of hydrogen evolution.

NMR spectroscopy provides an element-specific, sensitive probe of the local environment, enabling detailed information to be extracted. However, in the solid state the vast majority of this information remains unexploited, owing to the challenges associated with obtaining high-resolution spectra and the ease with which these can be interpreted. Recent advances enabling accurate and efficient calculation of NMR parameters in periodic systems have revolutionized the application of such approaches in solid-state NMR spectroscopy, particularly among experimentalists. As NMR is sensitive to the atomic-scale environment, it provides a potentially useful tool for studying disordered materials, and the combination of experiment with first-principles calculations offers a particularly attractive approach. There are, however, significant experimental and computational challenges in the application of NMR spectroscopy to disordered materials. For example, there is no longer a single arrangement of atoms in a simple model structure that matches the material under study, and many different atomic arrangements may be required to gain insight into the interpretation and assignment of NMR spectra, and ultimately, into the structure of the material under study.

The crystal chemical flexibility of pyrochlore-based (A₂B₂O₇) oxide materials has resulted in a wide range of applications, including energy materials, nuclear waste encapsulation and catalysis. There is, therefore, considerable interest in understanding the structure–property relationships in these materials, i.e., investigating how cation/anion disorder and local structure vary with composition. Here we combine a range of ⁸⁹Y, ¹¹⁹Sn and ¹⁷O NMR experiments with periodic planewave calculations to explore cation disorder in ¹⁷O-enriched (Y,La)₂(Sn,Ti,Zr,Hf)₂O₇ phases. We show how a variety of NMR crystallographic approaches from cluster-based approaches, to ensemble-based modelling and the use of grand canonical ensembles can provide insight into the atomic-scale structure and disorder in these materials.[1-6]

[1] Reader, S. W., Mitchell, M. R., Johnston, K. E., Pickard, C. J., Whittle, K. R., & Ashbrook, S. E. (2009). J. Phys. Chem C 113, 18874.

[2] Mitchell, M. R., Reader, S. W., Johnston, K. E., Pickard, C. J., Whittle, K. R., & Ashbrook, S. E. (2011). Phys. Chem Chem. Phys. 13, 488.

[3] Mitchell, M. R., Carnevale, D., Orr, R., Whittle, K. R., & Ashbrook, S. E. (2012). J. Phys. Chem . 116, 427.

[4] Fernandes, A., Moran, R. F., Sneddon, S., Dawson, D. M., McKay, D., Bignami, G. P. M., Blanc, F., Whittle K. R. & Ashbrook, S. E. (2018). RSC Advances 8, 7089.

[5] Moran, R. F., McKay, D., Tornstrom, P. C., Aziz, A., Fernandes, A., Grau-Crespo R., & Ashbrook, S. E. (2020). J. Am. Chem. Soc. 141, 17838.

[6] Fernandes, A., Moran, R. F., McKay, D., Griffiths, B., Herlihy, A., Whittle K. R., Dawson, D. M. & Ashbrook, S. E. (2020). Magn. Reson. Chem. in press, DOI: 10.1002/mrc.5140.

Structure elucidation of amorphous molecular solids presents one of the key challenges in chemistry today. Knowledge of the atomic-level structure in such materials would be of great value for example to direct the optimisation of pharmaceutical formulations. However, the lack of long-range structural order prevents atomic-level characterization of these materials using methods like single crystal X-Ray diffraction. Solid state NMR on the other hand yields atomic-level information on amorphous materials and molecular dynamics (MD) can generate candidate sets of possible disordered structures. Directly relating these two techniques has been out of reach so far, due to the prohibitive cost of computing chemical shifts on large ensembles of large MD structures using DFT. Recently, a method based on machine learning, dubbed ShiftML (1), has emerged as a quick and accurate way to predict the chemical shifts of organic solids, even for large systems.

Here, using a machine learning model of chemical shifts, we determine the complete atomic-level structure of the amorphous form of a drug molecule by combining dynamic nuclear polarization-enhanced solid-state NMR experiments with predicted chemical shifts for MD simulations of large systems (2). From these amorphous structures we then identify H-bonding motifs and relate them to local intermolecular interaction energies.

1. Paruzzo, F. M.; Hofstetter, A.; Musil, F.; De, S.; Ceriotti, M.; Emsley, L., “Chemical shifts in molecular solids by machine learning.” Nat Commun 2018, 9, 4501. doi.org/10.1038/s41467-018-06972-x

2. Cordova, Balodis, Hofstetter, Paruzzo, Nilsson Lill, Eriksson, Berruyer, Simões de Almeida, Quayle, Norberg, Svensk Ankarberg, Schantz, Emsley, "Structure determination of an amorphous drug through large-scale NMR predictions." Nat Commun 2021, doi.org/10.1038/s41467-021-23208-7

Complex structures with subtle atomic-scale details are now routinely solved using complementary tools such as X-ray and/or neutron scattering combined with electron diffraction and imaging. Identifying unambiguous atomic models for oxyfluorides, needed for materials design and structure−property control, is often still a considerable challenge despite the advantageous optical responses, magnetic properties, and energy storage capability of numerous oxyfluorides. Amongst the long-stranding challenges are the lack of tools to resolve fluorine and oxygen and to characterize fluoride-ion and MF_n polyhedral dynamics. In this work, NMR crystallography is used in combination with single-crystal X-ray diffraction, X-ray absorption spectroscopy, and property measurements to provide a comprehensive structural picture of a series of new oxyfluoride materials and highlight the presence of previously unidentified selective fluorine-mediated dynamics.

This talk will focus on insights from ¹⁹F NMR across early transition metal oxyfluoride materials including newly discovered hafnium oxyfluorides, spin singlet Mo(IV) cluster compounds, and emerging hybrid organic–inorganic low-dimensional compounds. The first system has relevance to fluoride-doped HfO₂ electronic materials [1]; the second example features a rare triangular metal oxyfluoride cluster, [Mo₃O₄F₉]⁵⁻ (Fig. 1) [2]; and the third series of compounds are structurally diverse and provide fundamental insights into competition between centrosymmetric and noncentrosymmetric crystallization [3]. Identifying the anion (dis)order is central to building design rules for noncentrosymmetric crystals with technologically relevant properties. 1D and 2D solid-state ¹⁹F NMR experiments are supported by ab initio calculations to shed light on the anion sublattice and to assign the numerous distinct fluorine environments. In compounds with ⁹³Nb and ⁵¹V, coupling between the metal and fluorine nuclei can be used to further aid the interpretation. Variable-temperature measurements reveal fluorine dynamics that are strongly correlated to polyhedral degrees of freedom. The dual scattering and spectroscopy approach is used to demonstrate the sensitivity of ¹⁹F shielding to small changes in bond length, on the order of 0.01 Å, even in the presence of hydrogen bonding, metal−metal bonding, and electrostatic interactions.

[1] Flynn, S., Zhang, C., Griffith, K. J., Shen, J., Wolverton, C., Dravid, V. P., Poeppelmeier, K. R. (2021). Inorg. Chem. 60, 4463.

[2] Ding, F., Griffith, K. J., Koçer, C. P., Saballos, R., Wang, Y., Zhang, C., Nisbet, M., Morris, A. J., Rondinelli, J. M., Poeppelmeier, K. R. (2020). J. Am. Chem. Soc. 142, 12288.

[3] Nisbet, M. L., Pendleton, I. M., Nolis, G. M., Griffith, K. J., Schrier, J., Cabana, J., Norquist, A. J., Poeppelmeier, K. R. (2020). J. Am. Chem. Soc. 142, 7555.

Three-dimensional electron diffraction crystallography (microED) can solve structures of sub-micrometer crystals, which are too small for single crystal X-ray crystallography. However, R factors for the microED-based structures are generally high (15-30% for small molecules) because of dynamic scattering. Thus, R factor may not be reliable provided that kinetic analysis is used. Consequently, there remains 1) ambiguity to locate hydrogens and 2) assignment of nuclei with close atomic numbers, like carbon, nitrogen, and oxygen. On the other hand, ¹H solid-state NMR is readily available using fast MAS probes and ¹³C, ¹⁴N, ¹⁵N, and ¹⁷O are completely different nuclei for NMR observation. Thus, information from solid-state NMR and microED is complementary.

Herein, we demonstrate combined approach using solid-state NMR and microED to solve crystalline structure. First, well established NMR crystallography approach is employed. Isotropic chemical shifts are very sensitive to local environment, thus crystalline structure, however, there are no intuitive way to predict chemical shifts from structures. GIPAW procedure paves a way to estimates chemical shifts of crystalline materials in a very high accuracy. This makes isotropic chemical shift as a reliable measure for structure validation. While wrong position of ¹H and misassignment of carbon/nitrogen/hydrogen result in poor agreement between experimental and calculated chemical shifts, right structure can be easily chosen among candidates. We show that this approach, which is well established with XRD structures, equally works well with microED. The crystalline structures are determined by microED and validated by isotropic chemical shifts [1]. To further validate the structure, next, we demonstrate another measure using dipolar-based ssNMR experiments in addition to isotropic chemical shifts. In principle, dipolar couplings provide useful information for structure elucidation, as the size of coupling is inversely proportional to the cube of internuclear distances. However, spin dynamics is often complicated due to presence of multiples of intra- and intermolecular couplings for small molecules, making structure elucidation difficult. On the other hand, it is readily calculated for given structures if the spin system is simple enough (< 8 spins). Here we utilize ¹H-¹H selective recoupling of proton (SERP) experiments [2-4] and ¹H-¹⁴N phase-modulated rotational-echo saturation-pulse double-resonance (PM-RESPDOR) as dipolar-based NMR experiments [5, 6]. While the former selects a subset of ¹H-¹H spin systems, the latter simplifies the spin system by decoupling ¹H-¹H interactions. As a result, SERP and RESPDOR probe ¹H-¹H and ¹H-¹⁴N networks, respectively. The structure is solved by microED and then validated by evaluating the agreement between experimental and calculated dipolar-based NMR results [7]. As the measurements are performed on ¹H and ¹⁴N, the method can be employed for natural abundance samples. Furthermore, the whole validation procedure was conducted at 293 K unlike widely used chemical shift calculation at 0 K using the GIPAW method.

[1] C. Guzmán-Afonso, Y.-l. Hong, H. Colaux, H. Iijima, A. Saitow, T. Fukumura, Y. Aoyama, S. Motoki, T. Oikawa, T. Yamazaki, K. Yonekura, Y. Nishiyama*, Nat. Commun. 10, 3537 (2019).

[2] N.T. Duong, S. Raran-Kurussi, Y. Nishiyama*, V. Agarwal*, J. Phys. Chem. Lett. 9, 5948-5954 (2018).

[3] N.T. Duong, S. Raran-Kurussi, Y. Nishiyama*, V. Agarwal*, J. Magn. Reson. 317, 106777 (2020).

[4] L.R. Potnuru†, N.T. Duong†, S. Ahlawat, S. Raran-Kurussi, M. Ernst, Y. Nishiyama* and V. Agarwal*, J. Chem. Phys. 153, 084202 (2020).

[5] N.T. Duong, F. Rossi, M. Makrinich, A. Goldbourt, M.R. Chierotti, R. Gobetto, Y. Nishiyama*, J. Magn. Reson. 308, 106559 (2019)

[6] N.T. Duong, Z. Gan, Y. Nishiyama*, Front. Mol. Biosci. 8, 645347 (2021).

[7] N.T. Duong, Y. Aoyama, K. Kawamoto, T. Yamazaki, Y. Nishiyama, under review.

The determination of active site protonation states is critical to gaining a full mechanistic understanding of enzymatic transformations; yet proton positions are challenging to extract using the standard tools of structural biology. Here we make use of a joint solid-state NMR, X-ray crystallography, and first-principles computational approach that unlocks the investigation of enzyme catalytic mechanism at this fine level of chemical detail. Through this process, we are developing a high-resolution probe for structural biology that is keenly sensitive to proton positions – rivaling that of neutron diffraction, yet able to be applied under conditions of active catalysis to microcrystalline and non-crystalline materials. For tryptophan synthase, this allows us to peer along the reaction coordinates into and out of the α-aminoacrylate intermediate. By uniquely identifying the protonation states of ionizable sites on the cofactor, substrates, and catalytic side chains, as well as the location and orientation of structural waters in the active site, a remarkably clear picture of structure and reactivity emerges. Most incredibly, this intermediate appears to be mere tenths of angstroms away from the preceding transition state in which the β-hydroxyl of the serine substrate is lost. The position and orientation of the structural water immediately adjacent to the substrate β-carbon suggests not only the fate of the hydroxyl group, but also the pathway back to the transition state and the identity of the active site acid-base catalytic residue. Reaction of this intermediate with benzimidazole (BZI), an isostere of the natural substrate, indole, shows BZI bound in the active site and poised for, but unable to initiate, the subsequent bond formation step. When modeled into the BZI position, indole is positioned with C-3 in contact with the α-aminoacrylate Cβ and aligned for nucleophilic attack.

Structural analysis by XRD still remains a considerable challenge for materials that can’t be isolated as single crystals. In NMR crystallography structural constraints are extracted from the modern solid-state NMR techniques, and along with DFT (density functional theory) calculations.[1-4] NMR crystallography has been used to derive de novo structures and to aid the refinement of X-ray powder diffraction data.[1-4] In this work, computational integration of advanced solid-state NMR with PXRD (powder X-ray diffraction) and modelling is used to understand the structure of metal coordination polymers that are produced by the etching of metal nanoparticles in acidic solution.[6-8] Notably, these coordination polymers have some structural disorder which gives rise to broadened diffraction peaks. Solid-state NMR was applied to determine the number of molecules in the asymmetric unit and give insight into the geometry at the metal center. Then, the PXRD pattern of the coordination polymers was partially indexed to find probable unit cells. The position of heavy atoms was then optimized within the unit cell using the Free Objects for Crystallography (FOX) software. Finally, Rietveld refinement and DFT optimization was used to obtain a final structural model. The final NMR and PXRD derived structure is validated by comparing the experimental and simulated PXRD pattern and NMR parameters. This protocol was verified on scandium acetate which has a known single crystal structure from the literature. The protocol was then successfully applied to microcrystalline gallium and aluminum coordination polymers. We anticipate that this methodology could be extended to similar kind of coordination polymers with inherent heterogeneous character.

Figure 1. Schematic representation of the NMR crystallography approach used for finding the crystal structure of the coordination polymer.

[1] Ashbrook, S. E. & McKay, D. (2016). Chem. Commun. 52, 7186–7204.

[2] Bouchevreau, B., Martineau, C., Mellot-Draznieks, C., Tuel, A., Suchomel, M. R., Trébosc, J., Lafon, O., Amoureux, J.-P. & Taulelle, F. (2013). Chem. – A Eur. J. 19, 5009–5013.

[3] Thomas, B., Rombouts, J., Oostergetel, G. T., Gupta, K. B. S. S., Buda, F., Lammertsma, K., Orru, R. & de Groot, H. J. M. (2017). Chem. – A Eur. J. 23, 3280–3284.

[4] Xu, Y., Southern, S. A., Szell, P. M. J. & Bryce, D. L. (2016). CrystEngComm. 18, 5236–5252.

[6] Rossini, A. J., Hildebrand, M. P., Hazendonk, P. A. & Schurko, R. W. (2014). J. Phys. Chem. C. 118, 22649–22662.

[7]Chang, B., Martin, A., Thomas, B., Li, A., Dorn, R., Gong, J., Rossini, A. & Thuo, M. ACS Mater. Lett. 2, 1211–1217.

[8] Chang, B. S., Thomas, B., Chen, J., Tevis, I. D., Karanja, P., Çınar, S., Venkatesh, A., Rossini, A. J. & Thuo, M. M. (2019). Nanoscale. 11, 14060–14069.

For over 60 years, nanomaterials have consistently attracted the attention of the scientific community. In the field of nanomedicine, recent effort toward optimizing the therapeutic efficacy of newly discovered active compounds has resulted in the development of original supramolecular systems that execute multiple functions. However, the true potential of these systems has not been entirely utilized. Advancing these materials calls for precise structural analysis of individual elements and a description of the mutual relations between them. This is a stringent requirement, as these systems exist at the borderline between crystalline and amorphous solids, for which high-quality diffraction data are inherently unavailable. This contribution thus addresses our attempt to formulate an efficient experimental-computational strategy for obtaining deep insight into the structure of complex polycrystalline composites with micro- and nanodomain architecture. To determine the atomic-resolution structure of these systems, we apply a procedure based on ¹H NMR crystallography extended to describe the component-selective data. This strategy is based on the combined application of domain-selective solid-state NMR spectroscopy (ss-NMR), crystal structure prediction (CSP), and density functional theory (DFT)-based calculations of NMR chemical shifts. This combination of experimental and theoretical approaches enables one to determine the structural arrangements of molecules in situations which are not tractable by conventional spectroscopic techniques. Its applications should be of particular importance for systems in which phase transformations can occur, and new polymorphic forms can be spontaneously created under the influence of the matrix environment. The potential of this combined analytical approach is highlighted using the recently developed biodegradable, injectable polyanhydride microbead formulation of decitabine (5-aza-2'-deoxycytidine, DAC), an archetypal DNA methyltransferase inhibitor used as an efficient therapeutic for epigenetic cancer therapy. In this innovative drug-delivery formulation, which was developed to circumvent the problem of hydrolytic lability of the active compound, a mixture of microcrystalline domains of decitabine and nanodomains of sebacic acid (SA) is embedded in the semicrystalline matrix of poly(sebacic acid-co-1,4-cyclohexane-dicarboxylic acid) (PSA-co-PCH) carrier. The proposed method, which employs the confluence of computational data with measured NMR parameters, thus provides for a way to distinguish between alternative candidate structures exclusively existing in the composite assembles, and to select the ones that are the most compatible with available information. As the obtained results also opened a route toward the structure refinement of synthetic polymers with a limited amount of spectroscopic data available, finding a procedure for the reliable generation of a representative set of CSPs of synthetic polymers is thus of paramount importance. This contribution thus demonstrates the synergy effects of the proposed combination of several experimental and computational procedures, which considerably extends the NMR crystallography approach into the area of intricate mixtures and nanostructured composites. Potentiality of this approach will be also highlighted in de-nuovo determination of the crystal structure of chemotactic N-formyl-L-Met-L-Leu-L-Phe-OH tripeptide.

NMR crystallography uses a combination of solid-state NMR (SSNMR), X-ray diffraction (XRD), and quantum chemical calculations for the determination and/or refinement of crystal structures.^1,2 Currently, the majority of NMR crystallographic studies reply upon the measurement and calculation of isotropic chemical shifts (CS) or CS tensors and their computation by density functional theory (DFT) methods; by contrast, electric field gradient (EFG) tensors of quadrupolar nuclei are used much less extensively.^3–6 EFG tensors at the origins of quadrupolar nuclei are sensitive to their surrounding electronic environments, including longer-range interactions that do not greatly influence chemical shifts, yielding unique sets of quadrupolar parameters for each magnetically distinct environment. Furthermore, EFG tensors are less computationally demanding to compute than CS tensors. Since EFG tensors are sensitive probes of local atomic environments, we believe that it is crucial to explore and develop quadrupolar NMR-based crystal structure prediction (CSP) methods within the context of modern plane-wave DFT computational packages. In particular, such methods would be very useful for the study and characterization of organic solids, including pharmaceutical drug products, nutraceuticals, and a wide variety of multi-component crystals.⁵

Herein, we demonstrate the use of experimentally-measured and computationally-derived ³⁵Cl EFG tensor parameters in a new NMR crystallographic protocol for the refinement of crystal structures, which are developed and optimized on a training set of four organic HCl salts with known crystal structures. The stages of this protocol include: (i) selection/assignments of molecular fragments, charges, motion groups, and potential unit cells; (ii) simulated annealing using the Polymorph software package to generate tens of thousands of candidate structures, (iii) coarse geometry optimizations using DFT-D2* methods (which include dispersion effects),^7–9 and (iv) subsequent fine geometry optimizations. Between each of these stages, filters involving the unit cell dimensions, EFG tensor parameters, and static lattice energies have been optimized to select for the best candidate structures. The robustness of this new protocol is demonstrated via comparison of EFG tensors, PXRD patterns, and overlays of the known and refined crystal structures. Finally, this new protocol is demonstrated in several blind tests for the structural determination and refinement of organic HCl salts with unknown structures.

(1) Taulelle, F. Encycl. Magn. Reson. 2009, 1–14.
(2) NMR Crystallography; Harris, R., Wasylishen, R., Duer, M., Eds.; John Wiley & Sons Ltd.: Chichester, U.K., 2009.
(3) Ashbrook, S. E.; McKay, D. Chem. Commun. 2016, 52, 7186–7204.
(4) Bryce, D. L. IUCrJ 2017, 4, 350–359.
(5) Hodgkinson, P. Prog. Nucl. Magn. Reson. Spectrosc. 2020, 118–119, 10–53.
(6) Widdifield, C. M.; Farrell, J. D.; Cole, J. C.; Howard, J. A. K.; Hodgkinson, P. Chem. Sci. 2020, 11, 2987–2992.
(7) Grimme, S. J. Comput. Chem. 2006, 27, 1787–1799.
(8) Holmes, S. T.; Vojvodin, C. S.; Schurko, R. W. J. Phys. Chem. A 2020, 124, 10312–10323.
(9) Holmes, S. T.; Schurko, R. W. J. Phys. Chem. C 2018, 122, 1809–1820.

Structure determination using Reverse Monte Carlo (RMC) relies on atomistic moves where, after each move, the target property is computed and compared to experiment. The move is accepted if improving the agreement and accepted only with a probability if not. Since of the order a few hundred million moves need to be performed, this requires very rapid evaluation of the property in question. Typical applications include X-ray and neutron scattering and EXAFS in single-scattering mode. Different experimental probes are sensitive to different structural aspects, however, and it can thus be advantageous to combine with, e.g., spectroscopic data to narrow down the range of solutions.

To this end we have developed SpecSwap-RMC [1-3] which performs RMC on a large library of potential structures with precomputed scattering and spectroscopic signals associated with each structure. A subset of structures is selected and all properties built from the selected structures and compared to the experimental data. The RMC is then performed by exchanging structures instead of moving atoms. A set of weights is then generated based on how often each structure is found in the sample set when probed. These SpecSwap-RMC weights can then be used to reweigh the library, to extract an average structure that is consistent simultaneously with all the supplied data.

I will give examples of applications to liquid water, where we combine X-ray diffraction (XRD) and multiple-scattering EXAFS [2], to ice where we use SpecSwap-RMC to analyse what structures have actually been measured in XAS on various samples [4], and discuss XRD, NMR, XAS and XES [5] data on liquid water.

[1] M. Leetmaa, K.T. Wikfeldt, L.G.M. Pettersson, J. Phys.: Cond. Mat. 22 (2010) 135001

[2] K.T. Wikfeldt et al., J. Chem. Phys. 132 (2010) 104513

[3] https://github.com/leetmaa/SpecSwap-RMC.

[4] I. Zhovtobriukh, P. Norman, L.G.M. Pettersson, J. Chem. Phys. 150 (2019) 034501

[5] I. Zhovtobriukh et al., Science China 62 (2019) 107010

Materials containing microporous networks are an important topic of study for the development of improved technologies for a wide variety of applications including catalysis and gas storage. Widespread interest in metal– and more recently covalent–organic frameworks (MOFs/COFs) endures due to wide-ranging topologies and functionalities imbued by apparently limitless combinations of structural building units. However, while the focus remains primarily on crystalline products, semantics of how to interpret said crystallinity can vary widely in different communities, sometimes leading to oversight of important aspects of the structure that have essential implications on the material properties, or help to understand formation and functionalization processes [1].

The characterization of layered COFs in particular is difficult due to the presence of only a few, low-angle peaks in their diffraction patterns. This has led to a longstanding, dichotomous relationship between expectations based on energetic calculations and the structures observed by diffraction. We have recently demonstrated an experimental resolution, by considering the total rather than just Bragg scattering, and pair distribution function (PDF) analysis, to show how high apparent symmetries can emerge from random, local offsets of the layers [2].

Equipped with a fresh tool-set to characterize these structures, this talk will discuss our on-going efforts in this area — leveraging different length-scale sensitivities of real- and reciprocal-space vantage points for building and fitting models to obtain a more precise depiction of the structural states contained within.

[1] Grunenberg, L., Savasci, G., Terban, M. W., Duppel, V., Moudrakovski, I., Etter, M., Dinnebier, R. E., Ochsenfeld, C. & Lotsch, B. V. (2021). J. Am. Chem. Soc. 143, 3430.
[2] Pϋtz, A. M., Terban, M. W., Bette, S., Haase, F., Dinnebier, R. E. & Lotsch, B. V. (2020). Chem. Sci. 11, 12647.

Development of novel electrode materials for intercalation type batteries have in the past focused on highly crystalline materials with the capability to retain long-range order during cycling. However, recent years have seen an increased interest for disordered materials, e.g. with the discovery of multiple high capacity electrodes based on disordered rock-salt structures or even completely amorphous materials exhibiting higher capacities than their crystalline counterparts [1,2]. Furthermore, it was recently showed by Ceder and co-workers, that long-range order is not a prerequisite for maintaining percolating intercalation pathways [3]. Still very little is known about the structural mechanisms behind order-disorder transitions induced by ion-intercalation or about ion-storage mechanisms in disordered mate-rials. This is in spite that fact that understanding these processes may also provide enhanced insights about how disorder influences the properties of traditional ordered electrodes.

Using operando synchrotron X-ray total scattering with pair distribution function analysis, we have studied a series of battery electrode materials, which undergo severe disordering during charge or discharge, i.e. during ion-extraction or -intercalation [4]. This allows us to map out the structural evolution during battery charge and discharge at the atomic-scale, and begin to understand the ion-storage mechanisms in such materials. The studied materials cover both Li-, Na and Mg-ion electrode materials composed of transition metal (Tm) oxides and phosphates with both layered and 3D-framework structures, e.g. Na_xTmO₂, Na_xFePO₄, Li_xTiO₂, Li_xV₂O₅ etc.[4] Our findings reveal that the order-disorder transition can occur both reversibly and irreversibly, via topotactic or completely reconstructive transitions and entail several disordering phenomena such as cation disorder, nano-crystallization, amorphization etc. This talk will illustrate the large variety in order-disorder phenomena within battery electrodes and highlight our methodology for the operando total scattering studies and pair distribution function analysis.

[1] Lee,, J., Kitchaev, D. A., Kwon, D.-H. Lee, J. K,. Papp, C.-W., Liu, Y.-S., Lun, Z., Clément, R. J., Shi, T., McCloskey, B. D., Guo, J., Balasubramanian, M., Ceder, G. (2018) Nature 556, 185-190.

[2] Uchaker, E., Zheng, Y. Z., Li, S., Candelaria, S. L., Hu, S., Cao, G. Z. (2014) J. Mater. Chem. A 2, 18208-18214.

[3] Lee, J., Urban, A., Li, X., Su, D., Mautier, G., Ceder, G. (2014) Science 343, 519-522.

[4] Christensen, C. K., Ravnsbæk, D. B. (2021) J Phys Energy DOI: 10.1088/2515-7655/abf0f1

To close the carbon cycle, the direct hydrogenation of CO₂ to methanol (CH₃OH) plays a key role allowing to convert a major greenhouse gas into a valuable energy carrier and platform chemical.^[1] Supported bimetallic catalysts are gaining increasing attention for CO₂ hydrogenation reaction due to the possibility of tuning their catalytic properties by judicious choice of the ratio of the alloying elements. The development of highly active and selective catalysts for CO₂ hydrogenation relies hence on obtaining a fundamental understanding of the relationship between a catalyst’s structure and its activity. However, heterogeneous catalysts are complex systems, typically composed of various phases and sites that exhibit different functionalities which requires the use of multiple and complementary techniques for their characterization. ^[2] X-ray absorption spectroscopy and atomic pair distribution function analysis (PDF) of X-ray total scattering data can provide detailed information on the structure of bimetallic supported nanoparticles. XAS, being element selective, allows to study the electronic state and geometry of each metal via XANES analysis (X-ray absorption near edge structure analysis) and their local atomic structure between ~1-5 Å by EXAFS (extended X-ray absorption fine structure) analysis. Probing the longer-range order (i.e. above ca. 5 Å) via EXAFS analysis is however challenging. PDF can interrogate the local to nanoscale structure of supported bimetallic nanoparticles, extending substantially the atomic length scale that can be studied, from ~1 Å up to several nanometers. In this presentation, we will show how XAS (Ni and Ga K-edges) and PDF analyses provide structural information of a series of Ni_xGa_y nanoparticles supported on SiO₂ (total metal loading of ca. 5 w.%). The PDF analysis was performed via a so-called differential PDF approach, i.e. subtracting the signal of the SiO₂ support and, thus, allowing us to characterize the nanocrystalline phases (disordered or intermetallic alloys) of the supported nanoparticles. Ga K-edge XANES and EXAFS reveal the presence of GaO_x species while Ni XANES and EXAFS confirm the presence of Ni⁰. Thus, combining the information obtained via XAS and PDF techniques is highly important to obtain a full atomic to nanoscale description of heterogeneous catalysts.

Crystalline phases are usually characterised by their periodic structures and space group symmetry. However, some crystalline materials have periodic structures only on average and deviate on a local scale. Several different locally ordered structures can exist with identical average periodic structure and space group symmetry, making them difficult to distinguish using regular crystallographic techniques.

Using high-quality single-crystal x-ray diffuse scattering the local order in thermoelectric half-Heusler Nb_1-xCoSb is investigated, for which different local orderings are observed. Half-Heusler materials have been intensely studied for their thermoelectric properties, but a general issue is their high thermal conductivity due to their simple structure. The defective half-Heuslers such as Nb_1-xCoSb have high vacancy concentrations (x=1/6), giving them much lower thermal conductivities than other half-Heusler compounds. From measurements on different samples of Nb_1-xCoSb, it is shown that crystals with identical stoichiometry and average crystal structure, but with different locally ordered structures, can be made by changing the synthesis method. The local structures in these samples are analysed using the three-dimensional difference pair distribution function (3D-ΔPDF).

A new method is shown which allows isolation of the substitutional correlations in the 3D-ΔPDF, showing that the vacancy distributions follow a vacancy repulsion model. Furthermore, the local structural relaxations around vacancies are quantised from analysis of Bragg peaks and 3D-ΔPDF. From the found short-range correlations, a physical model of the system is simulated using Monte-Carlo methods, and it is shown that the different samples correspond to the ground state and simulated quenched states of the model.

Advanced x-ray scattering techniques can unravel hidden local structures and for Nb_1-xCoSb these local structures can be controlled by the synthesis conditions. If the local structure of crystalline materials can be more generally related to the properties, then a new frontier in materials research will be available.

Aluminosilicate-based oxide-glasses are natural materials forming volcanic magmas [1] and frequently the main constituent of manufactured products like ceramic glazes, fiber optic materials and, more recently, biocompounds [2]. To characterise the atomic structure of these materials requires techniques sensitive to the very local structural environment, like spectroscopies (i.e. Nuclear Magnetic Resonance - NMR, Extended X-ray Absorption Fine Structure – EXAFS) and scattering methods (i.e. Total Scattering), due to their lack in periodic order that prevents the application of conventional crystallography. The oxide-glass structure is shaped by silicon centered corner-sharing tetrahedra, which can be combined, depending on composition, with aluminium centered motifs, while large cations like sodium, potassium and calcium tend to depolymerize the network, affecting, in this way, some of the glass properties, such as thermal expansion and glass transition temperature, as demonstrated in a previous study [3]. The glass structural complexity increases when their composition involves some intermediate element, like zinc and beryllium, whose role in the network can vary as a function of the bulk composition, see [4] for some examples. This is the case of the present study that is based on a structural modeling of 2 series of different aluminosilicate-based oxide-glasses with different zinc amounts (3 samples each series). These samples have been prepared by melt-quenching route at 1350°C and then measured by combining EXAFS spectroscopy (BM23 beamline, ESRF, France) with both neutron (SANDALS instrument, ISIS, UK) and synchrotron (ID11 beamline, ESRF, France) Total Scattering data. Zn K-edge EXAFS has been applied at the beginning, in order to evaluate some of the bond distances and the Zn geometrical environment, and this information is used later as constraints for total scattering data modelling, performed by the Empirical Potential Structure Refinement (EPSR) method [5]. The refinements show good residuals, as displayed in Figure 1 (on the left-hand side) and the results indicate that zinc is mostly 4-fold coordinated, but with some 3-fold, 5-fold and 6-fold species. In such complex glasses, therefore, the parameters describing the polymerization degree, like NBO (Non-Bonding-Oxygens), BO (Bonding Oxygens) and triclusters are not predictable by theoretical models, based on prior assumptions of the structural role of zinc. Figure 1 (on the right-hand side) shows the variations of NBO with ZnO mole fraction, comparing the results of this work and of theoretical calculations. Furthermore, the data modelling gave access to a wide number of structural parameters like bond angles, cluster size and cation charge compensating characteristics, that are valuable for further structure-properties studies.

Preservation and public accessibility of primary experimental data are cornerstones necessary for the reproducibility of empirical sciences. Many crystallography journals recommend that authors of manuscripts presenting a crystal structure deposit their primary experimental data (X-ray diffraction images) to one of the dedicated resources created in recent years. We present the Integrated Resource for Reproducibility in Molecular Crystallography (IRRMC). In its first five years, several hundred crystallographers have deposited over 9000 datasets representing more than 5,700 diffraction experiments performed at over 60 different synchrotron beamlines or home sources all over the world. We describe several examples of the crucial role that diffraction data can play in improving previously determined protein structures. In addition to improving the resource and annotating and curating submitted data, we have been building a pipeline to extract or generate the metadata necessary for seamless, automated processing. Preliminary analysis shows that about 95% of the data received by our resource can be automatically reprocessed. A high rate of reprocessing success shows the feasibility of automated metadata extraction and automated processing as a validation step that ensures the correctness of raw diffraction images. The IRRMC is guided by the Findable, Accessible, Interoperable, and Reusable data management principles. Data from IRRMC have already enabled several novel research projects.

Macromolecular crystallography (MX) is the dominant means of determining the three-dimensional structures of biological macromolecules. Over the last few decades, most MX data have been collected at synchrotron beamlines using a large number of different detectors produced by various manufacturers and taking advantage of various protocols and goniometry. These data came in their own formats, some proprietary, some open. The associated metadata rarely reached the degree of completeness required for data management according to Findability, Accessibility, Interoperability and Reusability (FAIR) principles. Efforts to reuse old data by other investigators or even by the original investigators some time later were often frustrated.

In the culmination of an effort dating back more than two decades, a large portion of the research community concerned with High Data-Rate Macromolecular Crystallography (HDRMX) agreed in 2020 to an updated specification of data and metadata for diffraction images produced at synchrotron light sources and X-ray free electron lasers (XFELs) [1]. This Gold Standard builds on the NeXus/HDF5 NXmx application definition and the International Union of Crystallography (IUCr) imgCIF/CBF dictionary and is compatible with major data processing programs and pipelines. It will ensure effortless automatic data processing, facilitate manual reprocessing of data independent of the facility at which they were collected, and enable data archiving according to FAIR principles, with a particular focus on interoperability and reusability.

Direct consequences of the Gold Standard are an unambiguous definition of the experimental geometry, a record of the synchrotron and beamline where the data were collected, and additional optional metadata that will make subsequent submission of the structural model to the PDB more straightforward. Just as with the IUCr CBF/imgCIF standard from which it arose and to which it is tied, the Gold Standard is intended to be applicable to all detectors used for crystallography. In particular, the application of the Gold Standard does not require the use of HDF5. Corresponding metadata definitions exist in CBF/imgCIF. All hardware and software developers in the field are encouraged to adopt and contribute to the standard.

The Gold Standard provides a convenient and consistent way to record the essential minimal data and metadata needed to process a wide range of macromolecular diffraction experiments including single axis, single crystal rotation experiments using single-module detectors, XFEL serial crystallography experiments using powerful multi-module detectors producing tens of thousands of images from huge numbers of small crystals, as well as synchrotron experiments producing large number of wedges from micro-crystals. Examples from all of these and more will be discussed.

[1] Bernstein, H.J., Förster, A., Bhowmick, A., Brewster, A.S., Brockhauser, S., Gelisio, L., Hall, D.R., Leonarski, F., Mariani, V., Santoni, G., Vonrhein, C. and Winter, G. (2020). Gold Standard for macromolecular crystallography diffraction data. IUCrJ, 7(5) 784 -- 792.

The work was supported in part by funding from Dectris Ltd., from the U. S. Department of Energy (BES KP1605010, KP1607011, DE-SC0012704), from the U. S. National Institutes of Health (NIGMS P30GM133893, R01GM117126).

Auto-Rickshaw [1,2] is a system for automated crystal structure determination. It provides computer coded decision-makers for successive and automated execution of a number of existing macromolecular crystallographic computer programs thus forming a software pipeline for automated and efficient crystal structure determination.

Auto-Rickshaw (AR) is freely accessible to the crystallography community through the EMBL-Hamburg AR Server [3].

Recently, it has been installed at the ASCI cluster at the Australian Synchrotron which uses Docker and Kubernetes system for launching AR jobs in high-throughtput manner. The synchrotron AR server is accessible to users from the MX beamline computers.

AR at the MX beamlines can be invoked through command line or a web-based graphical user interface (GUI) for data and parameter input and for monitoring the progress of structure determination. It can be also invoked via automatic data processing if the parameter inputs have been pre set at the AR-GUI during X-ray diffraction experiment.

A large number of possible structure solution paths are encoded in the system and the optimal path is selected as the structure solution evolves. The platform can carry out experimental (SAD, SIRAS, RIP or various MAD) and MR phasing or combination of experimental and MR phasing. The system has extended extensively for evaluation of multiple datasets for various phasing protocols as well as for evaluation of ligand binding and fragment screening.

The new implementation and features will be discussed during the presentation.

References

[1] Panjikar, S., Parthasarathy, V., Lamzin, V. S., Weiss, M. S. & Tucker, P. A. (2005). Auto-Rickshaw - An automated crystal structure determination platform as an efficient tool for the validation of an X-ray diffraction experiment. Acta Cryst. D61, 449-457.

[2] Panjikar, S., Parthasarathy, V., Lamzin, V. S., Weiss, M. S. & Tucker, P. A. (2009). On the combination of molecular replacement and single-wavelength anomalous diffraction phasing for automated structure determination Acta Cryst. D65,1089-1097.

[3] http://www.embl-hamburg.de/Auto-Rickshaw

Structural information, mainly derived by X-ray crystallography and Cryo-Electron Microscopy, is the quintessential prerequisite for structural-guided drug discovery. However, accurate structural information is only one piece of information necessary to understand the big picture of medical disorders. To provide a rapid response to emerging biomedical challenges and threats like COVID-19, we need to analyze medical data in the context of other in-vitro and in-vivo experimental results. Recent advancements in biochemical, spectroscopical, and bioinformatics methods may revolutionize drug discovery, albeit only when these data are combined and analyzed with effective data management framework like Advanced Information System proposed in 2017. The progress on AIS is too slow, but creating such a system is a Grand Challenge for biomedical sciences. By definition, a Grand Challenge is a challenging and extremely difficult long-term project that is not always appreciated by those looking for immediate returns.

Diffraction-limited synchrotron radiation sources (DLSRs) using the advanced accelerator technologies deliver high-brilliance X-rays at high repetition rates. The DLSRs are expected to provide X-ray diffraction (XRD) measurements with benefits such as a reduction of the total time required for a complete scan and an improvement of temporal resolution. At the proposed SPring-8-II facility [1], one of the DLSRs, anticipated experiments using XRD techniques require X-ray imaging detectors with a frame rate over 10 kHz, high pixel count, a count rate over 100 Mcps/pixel, and single-photon sensitivity. To meet these demands, we have been developing a high-speed X-ray imaging detector CITIUS (Charge Integration Type Imaging Unit with high-Speed extended-Dynamic-Range Detector) [2] for SPring-8 and SACLA. As for SPring-8, our first milestone is to install a 20M-pixel CITIUS detector in 2023. It has a frame rate of 17.4 kHz and a raw data rate of 1.4 TB/s. Such a high raw data rate demands the careful design of the data handling scheme from the transfer, on-the-fly processing, storage, to post-analysis.

In this presentation, we describe our plan on the data acquisition and analysis scheme and the current status of the development. Our baseline implementation of the data-processing flow is composed of two steps. At the first step, detector images are processed by on-the-fly processing such as accumulation and a veto mechanism, which reduces the peak data-stream rate from 1.4 TB/s to ~400 GB/s. The processing algorithms are implemented onto custom PCB boards (Data Framing Board, DFB). Each DFB has three field-programmable gate arrays (FPGAs). Then generated processed data are transferred via PCI Express 3.0 bus to PC server memory. The second step is to compress the images by PC servers. We are investigating several information-lossless compression algorithms including the one presented in [3]. The peak data rate after the compression is further reduced to ~10 GB/s. The compressed images are to be stored in cache storage with a capacity of about 4-day measurements. The cached data are transferred to the high-performance computing system for post-analysis, and long-term storage. We also present the results of the experiment using an X-ray photon correlation spectroscopy technique. We also present the infrastructure in detail to execute this flow.

[1] “SPring-8-II Conceptual Design Report” (Nov. 2014) http://rsc.riken.jp/eng/pdf/SPring-8-II.pdf. [2] T. Hatsui, “New opportunities in photon science with high-speed X-ray imaging detector Citius, and associated data challenge”, Presentation at the 2nd R-CCS International Symposium (2020) [3] R. Roy et al., the proceedings of CCGrid2021, accepted.

The structural dynamics of chemical systems can be investigated by in situ or operando X-ray experiments. Advanced and fast computational methods are needed to cope with the huge amount of data collected, and to extract precious information hidden in data through a model-free analysis. Data analysis approaches based on multivariate analysis are particularly suited to this aim, as they are able to efficiently process in a probe-independent way multiple measurements, by considering them as a whole data matrix [1].

We have developed a fully automatic and big-data set of computing procedures based on principal component analysis, which is able to process with the same algorithms in situ/operando X-ray diffraction and XAFS data to extract qualitative and quantitative information. The multivariate approach has been adapted to treat crystallographic data, by optimizing the directions of the principal components [2], or by including kinetic models in the extraction of the reaction coordinate [3]. The procedure includes several pre-processing strategies that can be applied on crystallographic and XAFS data; among them a peak-shift correction to disentangling lattice variations from changes of the atomic parameters [4]. The procedures have been implemented in the computer program RootProf [5], available from www.ic.cnr.it/ic4/en/software/. It can be also used for fast on-site analysis while running in situ experiments (Fig.1).

Here we show how in situ experiments coupled with new data analysis methods can disclose the structural mechanism underlying: i) the thermal adsorption of gas in zeolites [4]; ii) the non-isothermal solid-state synthesis of materials based on poly-aromatic molecular complexes [6]; iii) the temperature-induced transitions of metal halide perovskites [7].

Figure 1. The RootProf program processes data from in situ experiments to locate atoms responding to an external stimulus.

[1] Guccione, P., Lopresti, M., Milanesio, M., Caliandro R. Crystals 11, 12.

[2] Caliandro, R., Guccione, P., Nico, G., Tutuncu, G., Hanson, J.C. (2015). J. Appl. Cryst. 48, 1679.

[3] Guccione, P., Palin, L., Belviso, B. D., Milanesio, M., Caliandro R. (2018). Phys. Chem. Chem. Phys. 20, 19560.

[4] Guccione, P. Palin, L., Milanesio, M., Belviso B.D., Caliandro, R. (2018). Phys. Chem. Chem. Phys. 20, 2175.

[5] Caliandro, R., Belviso, B. D., (2014). J. Appl. Cryst. 47, 1087.

[6] Palin, L., Conterosito, E., Caliandro, R., Boccaleri, E., Croce, G., Kumar, S., van Beek, W., Milanesio M. (2016). CrystEngComm 18, 5930.

[7] Caliandro, R., Altamura, D., Belviso, B. D., Rizzo, A., Masi, S., Giannini. C. (2019). J. Appl. Cryst. 52, 1104.

In the last years a growing number of studies have been devoted, both experimentally and theoretically, to understanding the structural properties of disorder systems and chemical processes occurring in solution and more clear pictures are emerging. This was possible by the improvements of the experimental techniques and the development of more sophisticated and reliable theoretical models. As we will detail in this presentation, experimentally in the last years X-ray absorption spectroscopy (XAS) played a major role in unravelling many structural aspects of disordered systems and it was exploited to gain unprecedent information on chemical reactions occurring in solution. This was possible by coupling experiments with theoretical simulations and multivariate analysis, and by better exploiting the X-ray absorption near edge spectroscopy (XANES) that is very sensitive to three-dimensional structures. Here, we will show specific applications to several liquid systems and chemical reaction occurring in the ms time scale. Aqueous solutions containing lanthanoid and actinoid ions are analysed with the aim of providing a unified description of the hydration properties of these series. We will show how the combined approach using XAS and molecular dynamics simulations can be applied to the study of complex systems such as ionic liquids and deep eutectic solvents, that represent an innovative research field. Lastly, we will show how it is possible to shed light into mechanistic properties of bimolecular reactions in solution by combining XANES, UV-Vis with multivariate data analysis.

Tektites and impactites are mainly amorphous silicate glass bodies of impact genesis. The conditions, such as pressure (P), temperature (T), oxygen fugacity (fO₂), that existed during glass formation process influence the cation coordination. One of the common elements in impact glasses is iron, so it a useful probe of atmospheric parameters and collision conditions in geological history of Earth. X-ray absorption spectroscopy (XAS) is a direct probe of the local atomic structure around specific element applicable to liquids, single molecules or amorphous solids. Recent developments in theoretical interpretation of the X-ray absorption fine structure along with machine learning (ML) methods opened a new perspective for quantitative structural analysis of complex systems [1,2]. In this work we extend ML-driven fitting procedure to the amorphous structures of tektites, where several inequivalent sites with different coordination numbers can coexist. The analysis was performed in PyFitIt software [3]. For each possible coordination number N = 2…6 we constructed a fragment of silica where Fe ion was coordinated by several (SiO₄) tetrahedral units. Structural parameters of Fe(SiO4)_N cluster were varied to simulate possible bond length variation in amorphous silica both for Fe²⁺ and Fe³⁺ ions, e.g. all Fe-O distances were varied in the range [1.8…2.3 Å].

Figure 1 shows geometry parameters for the three-coordinated Fe ions: distance to the nearest oxygen, distance to the rest two oxygens, bending angle (distortions are marked with overlay of two structures for each of three deformations). In the space of structural parameters we selected a set of 700 points where XANES spectra were calculated by means of finite difference approach implemented within FDMNES software. These spectra were used as training set for machine learning method which established the relation between spectrum and structural parameters. The best quality of approximation was achieved for Radial Basis Functions method. After algorithm was trained the PyFitIt software allows user to predict structural parameters for a given spectrum in the input (so called direct method) or predict spectrum for a given set of structural parameters (so called indirect method, the analogue of multidimensional interpolation). Figure 2 shows the analysis of the Muong-Nong tektite spectrum. The two best fits are shown as red and blue lines and use a combination of 6-coordinated iron ions either with 4-coordinated or 3-coordinated species. The resulting parameters of two fits provided average coordination number <CN>=5.4±0.2 and average Fe-O distance <R>=1.96±0.04 Å which are in a good agreement with classical EXAFS analysis.

Copper molybdate (CuMoO₄) is a thermochromic and piezochromic material, which exhibits structural phase transitions under the influence of pressure and/or temperature that make this material perspective in chromic-related applications starting from the user-friendly temperature and pressure indicators to "smart" inorganic pigments.

Since the functional properties of CuMoO₄ are directly connected with its local structure, X-ray absorption spectroscopy (XAS) is an obvious choice to probe structural changes during temperature variation including the phase transition. However, the interpretation of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra is not straightforward and often requires the use of advanced simulation tools. Treatment of thermal fluctuations and static disorder in XAS is a complex task, which can be successfully addressed by reverse Monte-Carlo (RMC) method [1, 2].

In this study, we used XAS at the Cu and Mo K-edges to probe the temperature-induced evolution of the local structure of CuMoO₄ in the range from 10 to 973 K (Fig. 1). At low temperatures, the thermochromic phase transition between α-CuMoO₄ and γ-CuMoO₄ with a hysteretic behaviour was observed [3] while at temperatures above 400 K, the thermochromic properties of α-CuMoO₄ were related to temperature-induced changes in the O²⁻ → Cu²⁺ charge transfer processes [4].

The structural information encoded in the EXAFS spectra was extracted by RMC simulations based on an evolutionary algorithm (EA) implemented in the EvAX code [1]. This method allows one to obtain a structural model of such complex material as copper molybdate accounting for multiple-scattering effects as well as structural and thermal disorder contributions in the experimental EXAFS data. The structural models obtained by RMC were used to simulate the Cu K-edge XANES spectra at a high-temperature range, in which the temperature effect is the most pronounced. The simulated XANES spectra are in good agreement with the experiment and reproduce the main temperature-dependent XANES features.

[1] J. Timoshenko, A. Kuzmin, and J Purans, (2014) J. Phys.: Condens. Matter 26, 055401.

[2] I. Jonane, A. Anspoks, and A. Kuzmin, (2018) Model. Simul. Mater. Sci. Eng. 26, 025004.

[3] I. Jonane, A. Cintins, A. Kalinko, R. Chernikov, and A. Kuzmin, (2020) Rad. Phys. Chem. 175, 108411.

[4] I. Jonane, A. Anspoks, G. Aquilanti, and A. Kuzmin, (2019) Acta Mater. 179, 1901132.

Developments over the last two decades have achieved accuracies in attenuation coefficient and X-ray absorption fine structure of below 0.2%. This generally requires careful sample characterisation, monochromator and detector characterisation and additional experimental components to measure and correct for a range of systematics. More recently similar levels of accuracy have been obtained in fluorescence measurement. These techniques, XERT developed by Chantler, Barnea, Tran and group; and Hybrid, developed by Chantler, Tran, Best et al. offer accuracies and insight for disordered systems up to 100x more than previous work. To bring them to standard routine implementations for all users would strengthen hypothesis discrimination and testing for molecular and disordered structure and dynamics including for ideal crystals. In this they are complementary to XRD and ND investigations.

Over the past two years parts of this system have been implemented at the Australian Synchrotron with excellent precision and control of a range of systematics using XERT and Hybrid techniques in both transmission and fluorescence geometries.

Insight includes high accuracy of derived dynamical bond length, thermal parameters, consistency and inconsistency of energy offsets revealed from the data, and structural determination of nearby shells approaching an ab initio manner with XAS. It has allowed exploration of atomic form factors [1], XAFS dynamical bonding [2], electron inelastic mean free paths [3] and nanoroughness [4] appropriate for circuit quality control for microcomputers, with technological offshoots into detector and synchrotron diagnostics. As a consequence, the accurate characterization of fluorescence spectroscopy is developing [5], together with the accurate investigation of organometallic complexes. Further it has allowed investigation of several types of dynamic behaviour including the investigation of the reaction coordinate [6], thermal isotropy, and potentially Debye behaviour. The reaction coordinate investigations permit study of catalytic paths in Amyloid beta, and other electrochemical studies of ifficult or fragile organometallic systems in solid or solution form, at room temperature or in a cryostat.

Perhaps intriguingly, it has permitted the first X-ray measurements of electron inelastic mean free path [7]. This paper will explore the requirements for and applicability of higher accuracy in XAFS, the advantage of theory simultaneously fitting XANES and XAFS [8], and the opportunities for advanced dynamics and Debye studies, in addition to the potential for resolving challenges in catalytic and active centres.

The quality of XAFS data and the intrinsic information content can be outstanding, and its ability to determine bonding and dynamical modes can be unsurpassed. The talk will also look towards future opportunities not yet realised in advanced analysis and disorder measurement.

[1] de Jonge, MD et al., Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form-factor of tin over the energy range of 29 keV – 60 keV, Phys. Rev. A75 032702 (2007)

[2] Glover, JL et al. Measurement of the X-ray mass-attenuation coefficients of gold, derived quantities between 14 keV and 21 keV and determination of the bond lengths of gold, J. Phys. B 43 085001 (2010)

[3] Chantler, CT, Bourke, JD, X-ray Spectroscopic Measurement of the Photoelectron Inelastic Mean Free Paths in Molybdenum, Journal of Physical Chemistry Letters 1 2422 (2010); Bourke, JD, Chantler, CT, Phys. Rev. Lett. 104, 206601 (2010)

[4] Glover, JL et al., Nano-roughness in gold revealed from X-ray signature, Phys. Lett. A373 1177 (2009)

[5] Chantler, CT, et al., Stereochemical analysis of Ferrocene and the uncertainty of fluorescence XAFS data, J Synch. Rad.19 145 (2012)

[6] Best, SP et al., Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene, Chemistry - A European Journal, 22 18019-18026 (2016)

[7] Chantler, CT, Bourke, JD, Electron Inelastic Mean Free Path Theory and Density Functional Theory resolving low-Energy discrepancies for low-energy electrons in copper, Journal of Physical Chemistry A118 909-914 (2014)

[8] Bourke, JD et al., FDMX: Extended X-ray Absorption Fine Structure Calculations Using the Finite Difference Method, J Synchrotron Radiation 23 551-559 (2016)

Palladium nanocatalysts play significant role in wide range of reactions such as selective hydrogenation of alkynes. The information extracted during operando experiments on working catalysts allows us to consider various processes from a new point of view. In particular, X-ray absorption near edge structure (XANES) spectroscopy is a powerful tool widely applied for determining atomic and electronic properties of working catalysts [1]. In many cases, analysis of XANES data requires construction of theoretical models with a huge number of variable parameters. In this case, application of machine learning (ML) to in situ and operando XANES offers new horizons for structural characterization [2].

In this work, we discuss the construction of the theoretical models of palladium nanoparticles covering a big number of structural parameters. We investigate how the particle size, concentration of carbon impurities, which can be formed during hydrogenation of alkynes, and their distribution in the bulk and at the surface of palladium particles affect the Pd K-edge XANES features. We demonstrate step-by-step increasing similarity between the experimental difference spectra and theoretical model by increasing the complexity of the theoretical model, e.g. taking into account only interatomic distances (Fig. 1 dashed red), interatomic distances and carbon concentration (Fig. 1 dashed blue) and interatomic distances, carbon concentrations and particle size effects (Fig. 1 green line). Finally, we suggest a set of formal descriptors relevant to possible structural diversity and construct a library of theoretical spectra for ML-based analysis realized in PyFitit software [3].

Figure 1. Experimental difference Pd K-edge XANES for 2.8 nm Pd NPs in acetylene (solid black) and best fit results using theoretical spectra with interatomic distances only (dashed red), interatomic distances and carbon impurities in the bulk (dashed blue), and interatomic distances, carbon impurities in the bulk and surface (solid green) contribution as variable parameters. The best fit made by ML algorithm is represented by purple line [4].

[1] Bordiga, S., Groppo, E., Agostini, G., Bokhoven, J.A. & Carlo Lamberti, C. (2013). Chem. Rev. 113, 1736.

[2] Guda, A.A., Guda, S.A., Lomachenko, K.A., Soldatov, M.A., Pankin, I.A., Soldatov, A.V., Braglia, L., Bugaev A.L., Martini, A., Signorile, M., Groppo, E., Piovano, A., Borfecchia, E. & Lamberti, C. (2019). Catal. Today. 336, 3.

[3] Martini, A., Guda, S.A., Guda, A.A., Smolentsev, G., Algasov, A., Usoltsev, O., Soldatov, M.A., Bugaev, A., Rusalev, Yu., Lamberti, C. & Soldatov, A.V. (2019). Comput. Phys. Commun, 23, 107064.

[4] Usoltsev, O.A., Bugaev, A.L., Guda, A.A., Guda, S.A. & Soldatov, A.V. (2020) Top. Catal., in press.

Water and soil pollution by heavy metals and other hazardous compounds is a global problem threatening the entire biosphere and affecting the life of many millions of people around the world. For instance, approximately two million tons of industrial, sewage and agriculture waste are discharged every day into water, causing serious health problems and the death of many thousands of people every day on a worldwide basis. Design and assessment of technologies for immobilization and removal of hazardous elements (HEs) is one of the highest priorities for environmental protection both in the industrialized and the developing countries.

The incorporation of HEs into crystalline and glassy silicate ceramics (the “harder” geomaterials) provides a perfect example to show that modelling the preferential distribution and the efficiency of immobilization of HEs in the crystal lattice and vitreous phase requires a detailed crystallographic knowledge at both the long- (XRD) and the short- (XAS) range.

Concerning the application of “softer” geomaterials, crystallographic knowledge of the zeolite structures proved successful for removal of heavy metals and VOCs from contaminated water and for the clean-up of water polluted with antibiotics. Simultaneous toxic metal uptake and bacteria disinfection from aqueous solution was achieved using well characterized nanocomposites of both the softer (zeolite) and the harder (e.g. Fe₃O₄) geomaterials.

Despite cadmium being a toxic element for environmental and human health, it is widely used in industries for fabrication of nickel-cadmium batteries, as anticorrosive agent, color pigment, etc. The most common and effective techniques for Cd removal from wastewater include filtration, chemical precipitation, bio-remediation and ion exchange [1]. Because of their microporous structure and extremely efficient cation exchange capacity, natural zeolites are good candidates for use as ionic filters. Moreover, heavy-metal exchanged zeolites show improved catalytic properties that can be exploited in post remediation processes [2,3]. Therefore, the chemical reactivity and stability of heavy-metal enriched zeolite is of paramount importance. Additionally, the nature of the metal species and their interaction with the zeolite framework play a fundamental role. Nevertheless, the correct determination of the aforementioned aspects can be compromised by the high disorder of the extraframework species, making difficult an unequivocal interpretation of the coordination chemistry of the metal cations. In this respect, the combination of X-ray diffraction (XRD) based techniques together with X-ray absorption spectroscopy (XAS) represents a valid tool to probe the long and short-range order of the species of interest.

In this contribution, we used a complementary experimental and theoretical approach to investigate in detail the structure of two Cd²⁺ -exchangedzeolites, levyne (LEV) and erionite (ERI). These two minerals are classified as small-pore zeolites (pore size between 0.35 and 40 nm) and, due to their structural similarity, they are often found as intergrown phase in nature [4]. In this study, experimental data from single crystal XRD and XAFS were coupled with Molecular Dynamics (MD) simulations to determine the distribution and coordination chemistry of Cd²⁺ in the two framework types (LEV and ERI). Our results showed that in Cd-LEV, Cd²⁺ ions have a fairly ordered distribution, resembling that characteristic of the pristine material [5]. In contrast, a strong disorder of the extraframework species (Cd²⁺ and H₂O) is detected in Cd-ERI pores, where the occupancy of the EF sites is lower than 20%. Such disorder was attributed to the presence of Cd⁺²(H₂O)₆ complexes, which are only partially coordinated to framework oxygen and, therefore, more mobile. To discriminate between the effect of thermal and structural disorder in the measured and theoretically calculated EXAFS spectra, we propose a theoretical approach based on a set of geometry optimizations performed starting from the uncorrelated atomic configuration of MD simulations [6]. Moreover, based on EXAFS analysis, the formation of metallic Cd within the pores of both zeolites could be ruled out.

Finally, we present the effect of Cd²⁺ incorporation on the thermal stability of Cd-LEV. The structural changes were monitored in situ from 25 to 400°C by single crystal X-ray diffraction. Our results demonstrated that, even if Cd had little influence on the room temperature structure, the dehydration behaviour drastically changes compared to that of the pristine material (natural levyne-Ca). The most relevant differences can be summarized by: i) a stronger volume contraction of the unit-cell volume (8% and 5% for Cd-LEV and levyne-Ca [5], respectively) in the investigated temperature range, and ii) the lack, at high temperatures, of the phase transformation to levyne B’ topology, characteristic of natural levyne-Ca.

[1] Rodriguez-Narvaez, O. M, Peralta-Hernandez, J. M., Goonetilleke, A., Bandala, E. R. (2017). Chem. Eng. J. 323, 361.

[2] Onyestyak, G., Kallo, D. (2003) Microporous and Mesoporous Mater. 61, 199.

[3] Zhang, Y., Qu, Y., Wang, D., Zeng, X. C., Wang, J. (2017) Ind. Eng. Chem. Res. 56, 12508.

[4] Passaglia, E., Galli, E., Rinaldi, R. (1974) Contrib. Mineral. Petrol. 43, 253.

[5] Cametti, G. (2018) Microporous and Mesoporous Mater. 265, 162.

[6] Cametti, G., Scheinost, A. C., Churakov, S. V. (2021) Microporous and Mesoporous Mater. 313, 110835.

In recent years, the occurrence and fate of perfluoroalkyl substances (PFAS) in the aquatic environment was recognized as one of the emerging issues in environmental chemistry. In particular, PFOA (C8HF15O2) and PFOS (C8HF17O3S) have recently become the targets of global concern due to their ubiquitous presence in the environment, persistence, and bioaccumulative properties. Strong carbon-fluorine (C–F) bonds make PFOA and PFOS extremely resistant to chemical, thermal and biological degradation, consequently, their removal from water is a crucial scientific and social challenge [1-2]. This work aims to investigate, for the first time, the structural modifications and the desorption kinetics during the thermal activation of FAU and Ag-exchanged FAU-type zeolites used for removal of PFOA and PFOS from water. The introduction of Ag in the framework confers them unique physical, chemical, and antibacterial properties along with strong absorption property, good stability and catalytic activity [3]. In situ high-temperature synchrotron X-ray powder diffraction and thermal analysis coupled with Elemental Analyzer – Isotope Ratio Mass Spectrometry (EA-IRMS) provided to: i) investigate high temperature structural modifications experienced after during PFOA and PFOS thermal desorption and to check the crystallinity preservation of the porous matrix; ii) monitor and evaluate the organics decomposition process upon heating; iii) estimate the influence of Ag active sites in working zeolites; iv) verify the best regeneration temperature in order to verify whether they can be re-used for PFAS removal from wastewater. This information was crucial for designing and optimizing the regeneration treatment of such zeolites, which are revealed to be highly effective in water-remediation technology. Powder diffraction data of each sample were collected at the synchrotron MCX beamline (Elettra, Trieste, Italy) and were subjected to the same heat treatment profile encompassing the heating ramp with a rate of 5°C/min from room temperature to 800 °C. The powder samples were loaded and packed into a 0.5 mm quartz capillary open at one end and heated in situ using a hot air stream. The analysis of the patterns collected using in situ synchrotron XRPD on zeolites showed no heat-induced symmetry change. Moreover, to carry out a comparison, structural data relating to bare zeolites are also reported in order to check the contribution of the loaded organic molecules. The differential thermal analysis (DTA) curve shows two DTA exothermic events between 300 and 600 ºC due to the PFAs degradation, in very good agreement with the EA-IRMS analyses. The complete thermal regeneration of selected materials was achieved at ~600 and 750 °C for PFOA and PFOS loaded samples, respectively. No relevant variations were observed in Ag-exchanged materials. This information is crucial to examine the efficiency of Ag-exchanged zeolites compared to same samples taken separately for the adsorption of PFOS and PFOA from water. The diffraction peaks were also accurately monitored to study in real-time their evolution (in terms of broadening, shift, changes of intensities) compared with the Y zeolites without any treatment, after silver activation and as well as after PFOS and PFOA adsorption. The XRD analysis demonstrated that the adsorption/desorption process occurred without significant loss of zeolite crystallinity, but with slight deformations in the channel apertures. The regenerated zeolites regain the unit-cell parameters of the bare materials almost perfectly, however. Only a slight memory effect in terms of structural deformations is registered in channel geometry thus demonstrating that the regenerated samples which could be able to re-adsorb similar amounts of PFOS.

[1] Ferreira, L., Fonseca, A.M., Botelho, G, Almeida-Aguiar, C, Neves, I.C. (2012). Antimicrobial activity of faujasite zeolites doped with silver. Microporous and Mesoporous Materials. 160, 126–132.

[2] Kucharzyk, K.H., Darlington, R., Benotti, M., Deeb, R., Hawley, E. (2017). Novel treatment technologies for PFAS compounds: A critical review. Journal of Environmental Management. 204, 757-764.

[3] Ziwen, D., Denga, S., Bei, Y., Huang, Q., Wang, B., Huang, J., Yua, G. (2014). Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents—A review. Journal of Hazardous Materials. 274, 443–454.

Humans have used asbestos for about 5,000 years in various parts of the world [1] because of its outstanding properties. The massive use of asbestos turned out to be a global environmental problem when animal carcinogenicity tests and long-term epidemiological studies proved that inhalation of asbestos fibres may induce fatal lung diseases like asbestosis, carcinoma, malignant mesothelioma (MM) and many more after a latency period of decades [2].

Besides the morphological and chemical characterization conveyed by ESD-supported electron microscopy, X-ray diffraction is considered a reliable tool for the characterization of asbestos fibres. Due to problems of peak overlap in powder data, it is not possible though, to carry out a free refinement of these complex atomic structures in order to detect and measure subtle chemical changes to prove the biopersistence.

Since 2016, ID11 offered a new end station, called “nanoscope” where it is possible to focus the beam to the deep sub-micron scale. This is possible by using the in-line crossed silicon compound refractive lenses [3] and using a crossed pair of vertical and horizontal line foci. Combining the very small beam size with a diffractometer to align and maintain a sample in the beam during rotation is very promising for the crystallographic characterization of natural fibres. Here we report a proof of the in vivo biopersistence of asbestos fibres in human lung tissues (figure1) at the atomic scale using synchrotron micro-diffraction. We show that the atomic structure of an amosite fibre remained stable for about 40 years in the lungs of a subject diagnosed with malignant mesothelioma (MM) and originally exposed to a mixture of chrysotile, amosite and crocidolite [4].

Metal oxide aluminosilicate and aluminogermanate nanotubes, called imogolite nanotubes (INT), are nanotubes with well-controlled diameter and with different morphologies [1,2]. These nanotubes undergo major structural changes at high temperatures, including the transformation from one-dimensional nanochannels into a structure which is supposed to be lamellar [3,4].

Here, we report a complete analysis of the structural transformations of single and double-walled aluminogermanate nanotubes, up to 900°C. We applied an original approach combining (i) in-situ X-ray absorption spectroscopy measurements (LUCIA & DiffAbs beamlines, synchrotron SOLEIL), allowing us to investigate the evolution of both Al and Ge atoms coordination during the transformation process, and (ii) in-situ diffraction. It reveals that the dehydroxylation of nanotubes does not lead to a lamellar phase but to metastable intermediate states that we named “meta-imogolite” states by analogy with meta-kaolinite. A mechanism explaining the major structural reorganizations is proposed based on atomic jump processes. The understanding of these structural modifications represents a benchmark for further studies concerning the properties of transformed INT-based compounds.

[1] Paineau E. & Launois P. (2019) In. Nanomaterials from clay minerals. Amsterdam, Netherlands: Elsevier, pp. 257-284.

[2] Monet G., Amara M.S., Rouzière S., Paineau E., Chai Z., Elliott J.D., Poli E., Liu L.M., Teobaldi, G. & Launois P. (2018) Structural resolution of inorganic nanotubes with complex stoichiometry. Nat. Commun., 9, 2033.

[3] MacKenzie K.J.D., Bowden M.E., Brown I.W.M. & Meinhold R.H. (1989) Structure and thermal transformations of imogolite studied by ²⁹Si and ²⁷Al high resolution solid-state nuclear magnetic resonance. Clays Clay Miner., 37, 317-324.

[4] Zanzottera C., Vicente A., Armandi M., Fernandez C., Garrone E. & Bonelli B. (2012) Thermal collapse of single-walled alumino-silicate nanotubes: Transformation mechanisms and morphology of the resulting lamellar phases. J. Phys. Chem. C, 116, 23577-23584.

Naica's giant crystals caves have astonished scientists since their discovery in 2000. Their gypsum crystals have been the subject of extensive studies and reports, both on scientific aspects and general cultural news. This work reports a detailed investigation of the wall-crystal interface of a blocky type crystal pulled off the "Cueva de los Cristales" wall. At the interface, the zones that probably correspond to the nucleation and growth of the blocky were identified. Representative samples were extracted at different depths of the wall-crystal junction and studied by ICP-OES, light and electron microscopies, XRD, and synchrotron-based m-XRF and m-XANES methods. The interface layer, of an average thickness of about 30 to 60 mm, contains various crystalline and amorphous aggregates with diameters ranging from 1 to 30 mm. Calcite, silica, goethite, as well as several Pb, Mn, Cu, and Zn aggregates, have been identified as main components (Figure 1).

Figure 1.The wall-crystal interface of Cueva de los Cristales, with Fe and Zn μ-XRF and μ-XANES obtained from the sample.

The study of the shape and composition of these mineral aggregates, as well as the morphology of the wall-crystal interface, allowed deducing their transformation and role in crystal nucleation and growth. It has been concluded [1] that the nucleation and growth of the Naica giant crystals have occurred under conditions of a slightly supersaturated solution, almost in equilibrium, and stable over a long time. In addition, considering the non-classical theory of crystal nucleation [2] and the results presented here, we can formulate that the heterogeneous nucleation of the giant Naica crystals was initiated with the adsorption of nanocrystalline monomers. These clusters formed in the solution were successively physi- and chemisorbed on the cave walls and on the crystal surface, assembling the crystalline planes during the crystal growth.

The CONACYT (México), Projects 183706, 257912 and 270738, and Project MINECO(Spain) MAT2017-86168-R are acknowledged.

[1] Otalora, F. & Garcia-Ruiz, J. (2014). Chem. Soc. Rev. 43, 2013-2026.

[2] Van Driessche, A. E. S., Stawski, T. M. & Kellermeier, M. (2019). Chem. Geol. 530, 119274.μ