Hybrid organic-inorganic perovskite (HOIP) materials have shown immense potential in high performance photovoltaics. However, significant challenges remain for real-world applications. A fundamental understanding of how the organic cations within inorganic framework affect the structural phase transitions, and optoelectronic properties of the HOIP materials is desirable to design new materials and improve device performance. We have used the TOPAZ instrument at the ORNL Spallation Neutron Source to probe the role of hydrogen bonding in structural phase transition of HOIPs by collecting the 3D volume of diffraction pattern from the sample in neutron event mode. The array of the TOPAZ neutron time-of-flight detectors covers a large 3D-volumes of Q-space (after unit conversion of each event data from detector x, y and neutron wavelength l in diffraction space) for highly efficient reciprocal space surveys. Connecting the timestamp of event data with that of external stimuli provides the tools needed to resample the multidimensional dataset for temporal filtering of event-based single crystal neutron diffraction data. This approach has opened a new avenue to probe structural phase transitions and dynamics in real time.

In this presentation, I will show the result from a real-time variable temperature study (3D in diffraction, 1D in temperature) that established the path of the organic cation induced anomalous optoelectronic phenomenon in MAPbX₃, where MA is methylammonium, an organic cation that forms a network of hydrogen bonds with the halides X in the solid states. Data from real-time single-crystal neutron diffraction following the initiation of orthorhombic-tetragonal phase transition (Figure 1) provided details the change of hydrogen bonding pattern between the organic donor and the inorganic accepter, which not only induces the structural transition that results in anomalous red-shift of PL peak position as temperature increases, but also causes the decrease in dielectric screening, leading to the reduction of non-radiative recombination for stronger PL intensity.

Acknowledgement: The single-crystal neutron diffraction experiment was performed at the TOPAZ beamline of Oak Ridge National Laboratory’s Spallation Neutron Source, which is sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy.

Improvement of existing batteries is a hot topic due to both the rapid spread of mobile technologies and the impetuous growth of the electric vehicle sector. The commonly used lithium-ion batteries (LIB) have a number of well-known disadvantages: flammability and high lithium price due to limited natural resources. The moderate capacity of LIBs is a further challenge for high-performance mobile devices. Theoretically, all-solid-state batteries based on high-valent working ions, such as magnesium, zinc or aluminum, can have higher volumetric capacities compared to LIBs [1].

We report the results of the high-throughput search for new solid electrolytes (SE) and cathode materials for high-valent metal-ion batteries. We focused on Mg-, Ca-, Zn- and Al-containing ternary and quaternary chalcogenides. Theoretically, S-, Se- or Te-containing compounds should exhibit higher cation conductivities than their oxygen analogues. It can be explained by a lower degree of ionicity in chalcogenides in comparison to oxides [2]. Our study was performed by using a well-established high-throughput screening algorithm [3]. The algorithm consists of three main steps: (a) fast topological-geometrical screening; (b) bond valence site energy (BVSE) modeling for a preliminary quantitative estimation and (c) precise quantum-chemical modeling of ionic transport.

All ternary and quaternary Mg, Ca, Zn and Al chalcogenides (1572 structures) were extracted from the ICSD (version 2020/1). Among them, a group of promising cation conductors with 1D-, 2D-, or 3D-migration maps was identified by using the Voronoi partitioning algorithm as implemented in the ToposPro package [4]. We obtained 72 S-, 30 Se- and 11 Te-containing high-valent ion conductors. The BVSE method was utilized for determination of migration energies of all species in the compounds, and a group of most promising compounds with migration barriers E_m ≤ 0.5 eV and the difference in the migration energies with other ions ΔE_m ≥ 0.5 eV was selected. This group includes, in particular, MgLu₂Se₄, MgHo₂Se₄, ZnLa₃GaSe₇, Al_5.9SnTe_9.892, Al₂Be₂La₆S₁₄, Al_3.3Dy₆S₁₄, Al_3.3La₆S₁₄ compounds. In a final step, the density functional theory (DFT) modeling was carried out for the structures with lowest E_m compounds. The Nudged Elastic Band (NEB) method was used as implemented in the VASP package [5]. Figure 1 shows a good agreement of migration maps between the three applied approaches.

Figure 1. 3D Zn²⁺-migration map for ZnMn₂Te₄ compound in terms of crystallochemical analysis (a), bond valence site energies (b) and quantum-chemical modeling (c).

All results were uploaded to the web site http://batterymaterials.info, where they are available free of charge.

[1] Margilies, L., Kramer, M. J., McCallum, R. W., Kycia, S., Haeffner, D. R., Lang, J. C., Goldman, A. I. (1999). Rev. Sci. Instrum. 70, 3554.

[2] Chupas, P. J., Ciraolo, M. F., Hanson, J. C. & Grey, C. P. (2001). J. Am. Chem. Soc. 123, 1694.

[3] Bunge, H. J. (1982). Texture Analysis in Materials Science. London: Butterworth.

[4] Balzar, D. & Popa, N. C. (2004). Diffraction Analysis of the Microstructure of Materials, edited by E. J. Mittemeijer & P. Scardi, pp. 125-145. Berlin: Springer.

Keywords: Voronoi partitioning, ToposPro, BVSE-modeling, DFT calculations, high-valent ion conductors.

The work was done within Russian Science Foundation project no. 19-73-10026 and Russian Foundation for Basic Research grant no. 20-33-90018. T.L. acknowledges financial support of the German Federal Ministry of Education and Research (R2RBattery: 03SF0542A). Computational facilities of the «Zeolite» supercomputer (Samara Center for Theoretical Materials Science) were utilized for DFT calculations.

Zinc-group IV-nitrides are being considered as promising candidates for photovoltaic absorber materials, containing uniquely elements of low toxicity and low resource criticality [1] Further to band gap tuning by alloying group IV elements (Si, Ge, Sn), it has been postulated based on DFT calculations that these compounds possess a second mechanism for bandgap tuning through cation disorder [2]. While this intrinsic cation disorder is not straightforward to tune directly, we found that a degree of oxygen inclusion in the material triggers cation disorder and hence can mimic the effect. [3]

We have studied ZnGe(N,O)₂ as a model system, in which a large range of compositions can be accessed conveniently as bulk powder samples through ammonolysis reaction. [3,4] This does, however, afford the use of neutron diffraction for structural investigations, since Zn²⁺ and Ge⁴⁺ are isoelectronic and hence virtually indistinguishable by standard powder X-ray diffraction. [5]

Using chemical analysis, we established a simple model for the reaction mechanism and thereby reducing the complexity of the system to the general chemical formula Zn_1+xGe_1-x(O_xN_1-x)₂. This allows us to refine the neutron powder diffraction data with a highly reliable model and to extract accurate information on the cation disorder. We find that intrinsic cation disorder and cation disorder stemming from oxygen inclusion exist at the same time and we disentangle their effects on the optical bandgap of these materials.

[1] Narang, P., Chen, S., Coronel, N. C., Gul, S., Yano, J., Wang, L.-W., Lewis, N. S. & Atwater, H. A. (2014). Adv. Mater. 26, 1235–1241. [2] Skachkov, D., Quayle, P. C., Kash, K. & Lambrecht, W. R. L. (2016). Phys. Rev. B. 94, 205201. [3] Breternitz, J., Wang, Z., Glibo, A., Franz, A., Tovar, M., Berendts, S., Lerch, M. & Schorr, S. (2019). Phys. Status Solidi A. 216, 1800885. [4] Wang, Z. Y., Fritsch, D., Berendts, S., Lerch, M., Breternitz, J. & Schorr, S. (2021). under revision. [5] Wang, Z. Y., Savvin, S., Breternitz, J. & Schorr, S. (2021). in preparation.

Mössbauer spectroscopy is a very effective and in many cases a unique experimental method widely used to study the structural, magnetic, electronic, and phonon properties of various materials. The appearance of synchrotron methods based on Mössbauer resonance significantly expanded the range of tasks and led to the discovery of a number of new effects, for example, in the field of high pressure physics, superconductivity, magnetism of nano-objects, geophysics and others. In synchrotron installations, very high requirements are imposed on monochromatization of synchrotron radiation to ensure Mössbauer resonance conditions [1]. In the case of Mössbauer resonance on Fe-57 iron nuclei, the iron borate crystal FeBO₃ has the most optimal diffraction parameters appropriate for the final stage of monochromatization. Tuning to purely nuclear reflections in this crystal of the type (111) and (333), which are forbidden for X-ray diffraction, makes it possible to obtain an ideal Mössbauer radiation source.

However, very high requirements are imposed on the crystalline quality of such crystals, and their growth is a rather complicated technological task. Recently, we proposed a modernized method for growing single crystals based on iron borate FeBO₃ [2,3]. Meanwhile, for the required diffraction conditions, the FeBO₃ crystal should be heated to a temperature near the Néel point (about 348 K) [3,4]. In this case, deformations can occur in the crystal that distort or destroy the diffraction conditions. Therefore, an important task is the search and synthesis of crystals with similar diffraction properties, but with a Néel point near room temperature.

In this work we propose to apply the method of diamagnetic dilution and synthesized a series of single crystals with iron substitution by gallium in the series Fe_1‑xGa_xBO₃. The high quality Fe_1-xGa_xBO₃ single crystals with wide range of diamagnetic doping 0 ≤ x ≤ 1 were grown. The developed synthesis technique makes it possible to avoid cracks and imperfections of crystalline samples. The exact composition of the solid solutions was determined by energy-dispersive spectroscopy (EDS). Structural refinement of the Fe_1-xGa_xBO₃ crystals was performed by single crystal X-ray analysis (XRD). Electronic and magnetic properties of the crystals were studied by conventional Mössbauer spectroscopy. It is established that diamagnetic impurity leads to a slight rearrangement of the crystal structure and effect on the hyperfine parameters of the samples. We found that the magnetic properties of these crystals change significantly even with a small substitution of iron ions by gallium ions. From the temperature behavior of the Mössbauer spectra (Fig. 1), the Néel temperatures of Fe_1‑xGa_xBO₃ crystals for various gallium concentrations were determined.

Figure 1. The room-temperature Mössbauer spectra of FeBO₃ single crystals diluted by diamagnetic gallium with various concentrations. The direction of the propagation vector of the Mössbauer radiation k_γ is normal to the basic plane (ab) of the crystals.

The obtained data on the quality and nuclear diffraction parameters of the crystals at various temperatures will show the way of introducing functional impurities into FeBO₃ crystals to optimize the parameters of their operation in synchrotron experiments. Such crystals will be widely in demand at all synchrotrons of the third and fourth generations.

This study was funded by RFBR, project number 19-29-12016-mk.

[1] Potapkin, V., Chumakov, A. I., Smirnov, G. V., Celse, J.-P., Rüffer, R., McCammon, (2012). J. Synchrotron Radiat., 19, 559.

[2] Yagupov, S., Strugatsky, M., Seleznyova, K. et al. (2018). Cryst. Growth Des. 18, 7435.

[3] Smirnova, E.S., Snegirev, N.I., Lyubutin I.S. et al. (2020). Acta Cryst. B. 76, 1100.

[4] Snegirev, N., Mogilenec, Yu., Seleznyova, K. et al. (2019). IOP Conf. Ser. Mater. Sci. Eng, 525, 012048.

Keywords: iron-gallium borates single crystals, flux growth, XRD analysis, Mössbauer spectroscopy

Acrtuator materials convert input energy into mechanical motion. In recent years, organic actuator materials have attracted attention from the expectations of applications such as soft robots and flexible electronics. Among such actuation materials, photomechanical crystals are expected as a novel type of actuators because these crystals convert light energy into mechanical work due to photoisomerization of photochromic molecules. The actuation properties of photomechanical crystals should be characterized. However, deflection and force, which are crucial for actuators, are dependent on experimental conditions such as light intensity and crystal size, and thus the number of combinations under different conditions is infinite. This causes difficulty in obtaining the relationship between the experimental conditions and actuation outputs. To solve this problem with photo-bending crystals, we applied a machine learning-based regression approach, and then constructed response surfaces of deflection and force.

The deflection and force of the photo-bending crystal were analyzed in the following steps: (1) experimental observations/measurements of deflection and force, (2) feature extraction by exponential fitting, and (3) polynomial regression and variable selection (Fig. 1). In the first step, the deflection of the photo-bending crystal was observed by using a microscope, and the force was measured as the blocking force of the photo-bending (Fig. 1a). The deflection and force behaviors of the photo-bending crystal were measured by changing the light intensities and crystal sizes. In the second step, both deflection and force were fitted to exponential equations for bending and unbending processes and extracting features of the maximum value and time constants at all situations (Fig. 1b). In the third step, the obtaining features are analyzed using polynomial regression, variable selection, and analysis of variance to determine the parameters that influence deflection and force. Through this process, the response surfaces of deflection and force of a photo-bending crystal are statistically constructed by machine learning regression (Fig. 1c), and obtained models were interpreted by chemical and material mechanics. We have found that this machine learning-based regression is useful for relating experimental conditions and actuation outputs, and thus, can be used to control and optimize other functions of stimuli-responsive crystals. This research work was published as an article [1].

Two new compositional series with the previously unique γ-Ba₄Nb₂O₉ type structure, γ-Ba₄V_xTa_2-xO₉ and γ-Ba₄V_xNb_2-xO₉ (x = 0-2/3), have been synthesised via solid-state methods. Undoped Ba₄Ta₂O₉ forms a 6H-perovskite type phase, but with sufficient V doping the γ-type phase is thermodynamically preferred and possibly more stable than γ-Ba₄Nb₂O₉, forming at a 200 °C lower synthesis temperature. This is explained by the fact that Nb⁵⁺ ions in γ-Ba₄Nb₂O₉ simultaneously occupy 4-, 5- and 6-coordinate sites in the oxide sublattice, which is less stable than allowing smaller V⁵⁺ to occupy the former and larger Ta⁵⁺ to occupy the latter. We characterised the structures of the new phases using a combination of X-ray and neutron powder diffraction. All compositions hydrate rapidly and extensively (up to 1/3 H₂O per formula unit) under ambient conditions, like the parent γ-Ba₄Nb₂O₉ phase, and show moderate but improved mixed-ionic electronic conduction. At lower temperatures the ionic conduction is predominately protonic, while at higher temperatures it is dominated by oxide and electron-hole conduction.

Environmentally Friendly Rhodium(I) Model Catalysts tailored by various bidentate and monodentate (water soluble) ligand.

Z. G. Morerwa¹, Andreas Roodt¹ and Alice Brink¹

¹Department of Chemistry, University of the Free State, Bloemfontein, 9301, South Africa
E-mail: z.morerwa@gmail.com

Green chemistry aspires to meet sustainable development, while manufacturers are able to meet the needs of current economic development, without compromising the ability of future generations. It provides challenges to those who practice chemistry in industry, education and even research. Based on the benefits that it has in human health, environment and even the economy, it has become vital in changing the tarnished image of chemical research.

Aqueous organometallic chemistry receives much attention due to their many advantages in aqueous medium presented to stoichiometric and catalytic reactions.^{1, 2} Long term exposure of chemical pollution and waste which are absorbed through epidermal contact or inhalation can lead to deleterious effects on the respiratory, haematological and thyroid functioning.³ Hence the importance of replacing toxic solvents with greener alternatives is an important concept. The importance in a model water-soluble homogeneous rhodium (I) catalyst, with various N,O; O,O’; and N,N’ bidentate ligand, is to understand the relationship between activity and the catalyst structure.^4,5,6,7

This project focuses on the investigation of N,O; O,O’ and N,N’ bidentate 5 and 6 membered ring systems, in conjunction with water soluble tertiary phosphine ligands, in rhodium complexes and their potential application in catalysis. The goal is to synthesise a potentially effective water soluble rhodium catalyst that is easier to separate from the product, has high selectivity and activity, and is environmentally friendly. The aim is to focus on carbonylation, homologation and hydroformylation reactions, as well as water splitting reactions (to generate molecular hydrogen as energy source), in order to explore and to justify the proof of the concept.

[1] F. Joo´, Aqueous Organometallic Catalysis, Kluwer: Dordrecht, 2001.

[2] B. Cornils, W.A. Herrmann, Aqueous-Phase Organometallic Catalysis. Concepts and Applications, 1998, Wiley-VCH: Weinheim.

[3] N. Uzma, B.M.K.M. Salar, B.S. Kumar, N. Aziz, M.A. David, V.D. Reddy, Int. J. Environ. Res. Public Health, 2008, 3, 5.

[4] S.S. Basson, J.G. Leipoldt, A. Roodt, J.A. Venter, T.J. Van Der Walt, Inorg. Chim. Acta, 1986,119, 35.

[5] A. Roodt, G.J.J. Steyn, Recent Res. Devel. Inorgani. Chem, 2000, 2, 1.

[6] G.J.S. Venter, G. Steyl, A. Roodt, Acta. Cryst, 2011, 67, 11.

[7] Z.G. Morerwa, GJ.S. Venter, South African Journal of Science and Technology, 2019, 38, 1.

Keywords: Green chemistry; Model catalyst; Rhodium(I) complex; Water-soluble.

A systematic study of the synthesis, structural evolution as a function of temperature
by X-ray diffraction using Synchrotron Light (SL) radiation and electrochemical
behaviour using Electrochemical Impedance Spectroscopy (EIS) of REBa ₂Cu ₃O _6+δ (with RE = Nd, La and Y)
as cathode for IT SOFC.
Given the structure of the YBCO 123 (YBa ₂Cu ₃O _6+δ) system, the presence of mobile
oxygen vacancies and the possibility of synthesizing this type of ceramics
in our laboratory using a quick and straightforward technique, the study
of these structures as a possible IT - SOFC cathode was proposed.
A phase transition (o-T) was observed (for YBCO 123) at the same temperature at which a significant
decrease in the cathodic polarization resistance takes place.
These results led to the study of similar laminar perovskites replacing the Y cation with Nd and La.

Pyrochlore oxides, with the general formula A₂B₂O₇, are of considerable interest as catalysts for the oxygen evolution reaction^1-5, where A₂Ru₂O_7‑δ pyrochlores have recently emerged as state-of-the-art materials, and as photocatalysts for hydrogen evolution^6-8. Fundamental to their reactivity is the local-scale vacancy ordering and mobility, which can be tailored through cation substitution⁴. The chemical and structural flexibility of pyrochlore oxides gives them a diverse range of physical and chemical properties leading to technological applications including as fast-ion conductors^9-10, ferroelectrics¹¹, magnetism¹², oxide heterostructures^13-14, and host matrices for the immobilization of actinide-rich nuclear wastes¹⁵.

Atomic-scale disorder plays an important role in the chemical and physical properties of oxide materials. The structural flexibility of pyrochlore-type oxides allows for crystal-chemical engineering of these properties. Compositional modification can push pyrochlore oxides towards a disordered defect-fluorite structure with anion Frenkel pair defects that facilitate oxygen migration. The local structure of the long-range average cubic defect-fluorite was recently claimed to consist of randomly arranged orthorhombic weberite-type domains¹⁶. In this work we show, using low-temperature neutron total-scattering experiments, that this is not the case for Zr-rich defect-fluorites. By analyzing data from the pyrochlore/defect-fluorite Y₂Sn_2-xZr_xO₇ series using a combination of neutron pair distribution function and big-box modelling, we have differentiated and quantified the relationship between anion sub-lattice disorder and Frenkel defects. These details directly influence the energy landscape for oxygen migration and are crucial for simulations and design of new materials with improved properties.

1. Shang, C.; Cao, C.; Yu, D.; Yan, Y.; Lin, Y.; Li, H.; Zheng, T.; Yan, X.; Yu, W.; Zhou, S.; Zeng, J., Electron Correlations Engineer Catalytic Activity of Pyrochlore Iridates for Acidic Water Oxidation. Advanced Materials 2019, 31 (6), 1805104.

2. Oh, S. H.; Black, R.; Pomerantseva, E.; Lee, J.-H.; Nazar, L. F., Synthesis of a metallic mesoporous pyrochlore as a catalyst for lithium–O2 batteries. Nature Chemistry 2012, 4 (12), 1004-1010.

3. Cheng, F.; Chen, J., Something from nothing. Nature Chemistry 2012, 4 (12), 962-963.

4. Kuznetsov, D. A.; Naeem, M. A.; Kumar, P. V.; Abdala, P. M.; Fedorov, A.; Müller, C. R., Tailoring Lattice Oxygen Binding in Ruthenium Pyrochlores to Enhance Oxygen Evolution Activity. Journal of the American Chemical Society 2020, 142 (17), 7883-7888.

5. Abbott, D. F.; Pittkowski, R. K.; Macounová, K.; Nebel, R.; Marelli, E.; Fabbri, E.; Castelli, I. E.; Krtil, P.; Schmidt, T. J., Design and Synthesis of Ir/Ru Pyrochlore Catalysts for the Oxygen Evolution Reaction Based on Their Bulk Thermodynamic Properties. ACS Applied Materials & Interfaces 2019, 11 (41), 37748-37760.

6. Allured, B.; DelaCruz, S.; Darling, T.; Huda, M. N.; Subramanian, V., Enhancing the visible light absorbance of Bi2Ti2O7 through Fe-substitution and its effects on photocatalytic hydrogen evolution. Applied Catalysis B: Environmental 2014, 144, 261-268.

7. Wu, J.; Zhou, C.; Zhao, Y.; Shang, L.; Bian, T.; Shao, L.; Shi, F.; Wu, L.-Z.; Tung, C.-H.; Zhang, T., One-Pot Hydrothermal Synthesis and Photocatalytic Hydrogen Evolution of Pyrochlore Type K2Nb2O6. Chinese Journal of Chemistry 2014, 32 (6), 485-490.

8. Kuriki, R.; Ichibha, T.; Hongo, K.; Lu, D.; Maezono, R.; Kageyama, H.; Ishitani, O.; Oka, K.; Maeda, K., A Stable, Narrow-Gap Oxyfluoride Photocatalyst for Visible-Light Hydrogen Evolution and Carbon Dioxide Reduction. Journal of the American Chemical Society 2018, 140 (21), 6648-6655.

9. Radhakrishnan, A. N.; Rao, P. P.; Linsa, K. S. M.; Deepa, M.; Koshy, P., Influence of disorder-to-order transition on lattice thermal expansion and oxide ion conductivity in (Ca_xGd_1−x)₂(Zr_1−xM_x)₂O₇ pyrochlore solid solutions. Dalton Transactions 2011, 40 (15), 3839.

10. Garcia-Barriocanal, J.; Rivera-Calzada, A.; Varela, M.; Sefrioui, Z.; Díaz-Guillén, M. R.; Moreno, K. J.; Díaz-Guillén, J. A.; Iborra, E.; Fuentes, A. F.; Pennycook, S. J.; Leon, C.; Santamaria, J., Tailoring Disorder and Dimensionality: Strategies for Improved Solid Oxide Fuel Cell Electrolytes. ChemPhysChem 2009, 10 (7), 1003-1011.

11. McQueen, T. M.; West, D. V.; Muegge, B.; Huang, Q.; Noble, K.; Zandbergen, H. W.; Cava, R. J., Frustrated ferroelectricity in niobate pyrochlores. Journal of Physics: Condensed Matter 2008, 20 (23), 235210.

12. Thygesen, P. M. M.; Paddison, J. A. M.; Zhang, R.; Beyer, K. A.; Chapman, K. W.; Playford, H. Y.; Tucker, M. G.; Keen, D. A.; Hayward, M. A.; Goodwin, A. L., Orbital Dimer Model for the Spin-Glass State in Y₂Mo₂O₇. Physical Review Letters 2017, 118 (6).

13. O'Sullivan, M.; Hadermann, J.; Dyer, M. S.; Turner, S.; Alaria, J.; Manning, T. D.; Abakumov, A. M.; Claridge, J. B.; Rosseinsky, M. J., Interface control by chemical and dimensional matching in an oxide heterostructure. Nature Chemistry 2016, 8 (4), 347-353.

14. Poeppelmeier, K. R.; Rondinelli, J. M., Mismatched lattices patched up. Nature Chemistry 2016, 8 (4), 292-294.

15. Ewing, R. C.; Weber, W. J.; Lian, J., Nuclear waste disposal—pyrochlore (A₂B₂O₇): Nuclear waste form for the immobilization of plutonium and “minor” actinides. Journal of Applied Physics 2004, 95 (11), 5949-5971.

16. Shamblin, J.; Feygenson, M.; Neuefeind, J.; Tracy, C. L.; Zhang, F.; Finkeldei, S.; Bosbach, D.; Zhou, H.; Ewing, R. C.; Lang, M., Probing disorder in isometric pyrochlore and related complex oxides. Nature Materials 2016, 15 (5), 507-511.

Li-ion batteries have transformed daily life by acting as energy dense, rechargeable power sources for a wide range of electronic devices. As part of the UK Faraday Institute FutureCat [1] project we are investigating a range of new lithium-ion battery cathode materials for application in all-electric vehicles. In addition to the normal requirements of maximizing energy density and power output, as part of this project we are also trying to move away from cobalt-based materials due to their poor environmental impacts; we have focused on materials containing earth-abundant elements, with a particular emphasis on iron-based materials. Most of the iron, in particular, Fe³⁺ materials, that have been investigated to-date suffer from a capacity loss after long term cycling, although a good performance can be achieved for the first cycle [2]. This capacity loss is generally attributed to the easy migration of Fe³⁺ between different coordination sites. To get more insight into these issues, we are currently investigating a novel Fe-based system, LiFe_2-xIn_xSbO₆.

In the present work, we have performed a detailed structural characterization of the different members of the solid solution, as well as their electrochemical properties. Based on these results, we will discuss the implications of partial substitution of Fe by In over the electrochemical performance of these Fe-based materials.

[1] https://futurecat.ac.uk/

[2] Li, J. L., Jianjun. Luo, Jing. Wang, Li. He, Xiangming., Recent advances in the LiFeO2-based materials for Li-ion batteries. Int. J. Electrochem. Sci. 2011, 6, 1550-1561.

Solid Oxide Fuel Cells (SOFCs) and Solid Oxide Electrolyser Cells (SOECs) are exciting electrochemical devices that provide unique and revolutionary solutions to some of the renewable energy challenges facing society. The architype materials used as solid electrolyte in most devices include YSZ (Yttrium stabilised Zirconia) and CaSZ (Calcium stabilised Zirconia) with the Y or Ca dopants present at around 8 to 10% level. As the performance characteristics of these materials are not completely satisfactory, there is a definite need for improved alternatives. Particularly Doped Cerate and Bismuthate are being investigated as alternatives. Although it is well established that most conducting phase of these is cubic with average structure features consistent with the Flourite structure, there have been only a few no reports of studies into the nano-structure or local structures of these materials The nuanced structural details of these materials are thus not yet clear, and certainly play a significant role in the important properties of the materials. Within this context our research has focused on gaining a fundamental understanding of the mechanisms governing the transport properties of these and closely related materials such as δ-Bi₂O₃ which has the highest reported oxides ionic conductivity for the (BiO_1.5)_0.88(DyO_1.5)_0.08(WO₃)_0.04 case [1], as well as the role of the various doped variants in these structure-property relationships. Typically the cubic forms of these materials exhibit higher oxygen ionic conductivity due to the presence of vacant anionic sites, and exists only at elevated temperatures. In most cases doping results in only a meta-stable cubic phase that slowly transitions to a less conducting phase. From a collection of almost 400 distinct chemical compositions we have learnt that the nature, number and concentration of the dopents used, all affect the conductivity and stability of the desired phase in a complicated manner.

I will present a selection of our results to date. Including our PDF & PXRD analysis of the scattering data we measured at ID-22 at the ESRF, as well as at 28-ID-1 at NSLS-II. Variations in the respective thermoresponsive behaviours clearly shows structural variations when comparing the structure as perceived on the nano-scale with the bulk average structure

[1] N. Jiang et al, “A higher conductivity Bi2O3-based electrolyte”, Solid State Ionics 150 (2002) 347– 353

Piezoelectric crystals, which exhibit electric polarization under mechanical stress and a mechanical strain under an electric field, are widely used in various electro-mechanical devices such as oscillators, sensors, and actuators. The mechanism of piezoelectricity can be simply explained by displacements of cations and anions against each other under a mechanical stress or an electric field. The actual relationship between a lattice strain and atomic displacements induced by the application of an electric field should be revealed by X-ray diffraction (XRD) structural analysis under an electric field. However, atomic displacements induced by inverse piezoelectric effects are usually very small to detect by conventional XRD measurements.

We have recently succeeded in detecting such small atomic displacements in piezoelectric oscillators of α-quartz (SiO₂) and langasite-type crystals (La₃Ga₅SiO₁₄ and Nd₃Ga₅SiO₁₄) under alternating electric fields by using a combination of resonant mechanical vibration and time-resolved XRD [1-3]. The amplitudes of the mechanical vibration of piezoelectric oscillators under an alternating electric field were resonantly enhanced at the fundamental resonant frequency. The time dependences of the enhanced lattice strain and atomic displacements during resonant mechanical vibration were measured by time-resolved XRD using short-pulse X-rays from a synchrotron radiation source and a high-repetition-rate X-ray chopper [4]. The time-resolved crystal structure analyses of the α-quarts and langasite-type crystals revealed that bridging angles of oxygen tetrahedra (SiO₄ and GaO₄) are deformed with displacements of specific oxygen atoms along the applied electric field during the resonant vibrations. Deformations of specific oxygen tetrahedra were also observed in the langasite-type crystals. This seems the reason why the piezoelectric constants d₁₁ of the langasite-type crystals are larger than that of α-quarts. Gallium phosphate (GaPO₄) is a piezoelectric crystal with the structure consisting of GaO₄ and PO₄ tetrahedra. To reveal the difference between GaO₄ and PO₄ tetrahedra in response to an electric field, time-resolved crystal structure analysis of a resonantly vibrating GaPO₄ crystal under an alternating electric field was performed in this study.

A commercial GaPO₄ oscillator with the fundamental resonant frequency of 5.8 MHz was used in the XRD measurement under an alternating electric field. The XRD measurement was performed at beamline BL02B1 of SPring-8 large synchrotron radiation facility. Resonant vibration of the GaPO₄ oscillator under a sine-wave electric field was synchronized with repetitive short-pulse X-rays with a pulse width of 50 ps extracted at 2.6 kHz by the high-repetition-rate X-ray chopper [4]. The time dependence of momentary XRD data was measured by tuning the delay time of the sine-wave electric field to the short-pulse X-rays. The β and γ angles of the C-centred orthorhombic lattice converted from the trigonal lattice are deformed from 90° by a thickness-shear strain under an electric field. The time dependence of Δγ = γ − 90° of the resonantly vibrating GaPO₄ oscillator under an alternating electric field with the amplitude of 0.17 MV/m reaches 0.23° at the maximum. The maximum ǀΔγǀ is ~10³ times larger than ǀΔγǀ under a static electric field with the strength of 0.17 MV/m. We revealed the differences between the crystal structures of the resonantly vibrating GaPO₄ at the moments when the γ angle reaches the minimum and maximum.

[1] Aoyagi, S., Osawa, H., Sugimoto, K., Fujiwara, A., Takeda, S., Moriyoshi, C., & Kuroiwa, Y. (2015). Appl. Phys. Lett. 107, 201905.

[2] Aoyagi, S., Osawa, H., Sugimoto, K., Takeda, S., Moriyoshi, C., & Kuroiwa, Y. (2016). Jpn. J. Appl. Phys. 55, 10TC05.

[3] Aoyagi, S., Osawa, H., Sugimoto, K., Nakahira, Y., Moriyoshi, C., Kuroiwa, Y., Takeda, H., & Tsurumi, T. (2018). Jpn. J. Appl. Phys. 57, 11UB06.

[4] Osawa, H., Kudo, T., & Kimura, S. (2017). Jpn. J. Appl. Phys. 56, 048001.

In industrial as well as research laboratories, the demand for the analysis of thin films and coatings has been growing, thanks to the development of a large variety of applied materials. Such materials are for example used in photovoltaic collectors for green energy harvesting, vice versa as materials for generating light in LEDs and Lasers or as materials for sophisticated optical applications.

X-ray diffraction (XRD) is one of the commonly used analysis techniques to characterize the crystallographic structure of thin films and coatings. Determining the thickness of layers can be challenging but is important to control the properties of the materials. Both, X-ray reflectometry (XRR) and X-ray fluorescence spectroscopy (XRF) allow determining the thickness of layers even in multi-stack systems. The applicability of both methods depends on the composition and nature of the sample. On the other hand, controlling the crystallographic nature of the deposited material is crucial because physical properties like electric conductivity or transparency depend on it.

Recently a less hazardous alternatives for CdS which is used as a buffer material in CIGS (Copper Indium Gallium Selenide) solar cells was investigated.^[1] Such solar cells are advantages compared to more common bulk solar cells because of the reduced requirement of resources. Additionally, the interest in thin film battery materials is showing an increase because it enables unique battery solution e.g. batteries directly on chips or flexible batteries. More commonly optical coatings are used in smart phone camera lenses and even as optics for X-ray analytical instrumentation.

Technological advancement allows for miniaturization and therefore leads to more capable benchtop solutions. The Thermo Scientific™ ARL™ EQUINOX benchtop powder diffractometers and the ARL™ Quant’X benchtop energy dispersive X-ray fluorescence spectrometer (EDXRF) are both designed to conveniently carry out measurements on thin film samples of various types

[1] N. Winkler, R. A. Wibowo, W. Kautek, T. Dimopoulos, J. Mater. Chem. C, 2019, 7, 3889.

Low-temperature cooling is a necessary requirement in many areas of fundamental research and applied technologies. Many applications, including quantum computing¹, spintronics² and medical imaging, rely on liquid helium to operate at temperatures below 20 K. In particular, liquid helium ⁴He is used for T > 2 K and a mixture of the two isotopes ³He and ⁴He is commonly employed for cooling below this. Liquid helium is costly, expensive and prone to disruptions in supply,³ so it is necessary to explore efficient and cost-effective alternatives. Paramagnetic magnetocalorics⁴ are great He-free candidates for low-temperature cooling, with much higher thermodynamic efficiencies below 20 K than cryocoolers, although most magnetocalorics are tailored for use below 1 K and very high applied fields.

Recent work on coordination frameworks have shown compounds, such as Gd(HCO₂)₃ and GdOHCO₃, having comparable or greater MCEs than Gd₃Ga₅O₁₂ (GGG), the benchmark magnetocaloric for cooling below 10 K, with the incorporation of other lanthanides leading to excellent performance above 4 K in low applied fields.^5,6,7 Inspired by these results we have synthesised members of the Ln(HCO₂)(C₂O₄) family (Ln = Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺) that crystallise in the orthorhombic Pnma space group and feature low-dimensional chains arranged on a distorted triangular lattice. We have studied the magnetic properties and MCE of these materials.

We have found Gd(HCO₂)(C₂O₄) to be an excellent candidate for applications at around 2 K with one of the highest magnetocaloric entropy changes amongst coordination frameworks. Generally, the incorporation of Ising-like cations was previously shown to lead to improved performance at higher temperatures under low applied fields that can be generated more easily using permanent magnets. We have observed this only for Dy(HCO₂)(C₂O₄), in contrast with results found for the Ln(HCO₂)₃ and LnOHCO3 families of compounds. Indeed, characterisation using neutron diffraction indicates these Ising compounds lack the strong local magnetic correlations found in the related analogues, indicating this negatively affects the optimisation of the MCE performance for these compounds.⁷

References

1. L. Gyongyosi and S. Imre, Comput. Sci. Rev., 2019, 31, 51–71.
2. C. Mitra, Nat. Phys., 2015, 11, 212–213.
3. A. H. Olafsdottir and H. U. Sverdrup, Biophys. Econ. Sustain., 2020, 5, 6
4. .A. Smith, Eur. Phys. J. H, 2013, 38, 507–517.
5. G. Lorusso, J. W. Sharples, E. Palacios, O. Roubeau, E. K. Brechin, R. Sessoli,A. Rossin, F. Tuna, E. J. L. L. McInnes, D. Collison and M. Evangelisti, Adv.Mater., 2013, 25, 4653–4656.
6. R. J. C. Dixey and P. J. Saines, Inorg. Chem., 2018, 57, 12543–12551.
7. P. J. Saines, J. A. M. Paddison, P. M. M. Thygesen and M. G. Tucker, Mater. Horizons, 2015, 2, 528–535.

The performance, properties and function of electrochemical energy storage materials is not only rooted in their chemistry but also in their structure and transport behaviour at the atomic and nanometer scale. Investigative techniques for elucidating the structural evolution of these materials are scarce, which makes it hard to obtain a deeper mechanistic knowledge.

Operando small- and wide-angle X-ray scattering (in situ SAXS/WAXS) can in general provide such structural and dynamic information of electrochemical reaction products, solvation processes in complex electrode materials, etc. In this contribution we present a unique electrochemical cell which can be used for performing combined electrochemical scattering studies on a laboratory SAXS/WAXS system. It allows analysing a variety of electrochemical and electrochemical storage materials such as metal-ion/metal-air batteries, nanoparticle intercalation-type materials as well as supercapacitors. The optimized cell design ensures short diffusion pathways and fast electrochemical processes along with excellent scattering data quality.

Different application examples are discussed, including the nanoscale phase evolution in lithium-air batteries and structural studies of nanoporous carbons which are applied in batteries and hybrid supercapacitors.

Prehal C. et al., Nat Commun, 11, 4838 (2020)
Prehal C., Freunberger S. et al., PNAS April 6, 2021 118 (14)

NASICON-type LiTi₂(PO₄)₃ (LTP, space group R-3c) has been studied as a potential solid-state electrolyte material in Li ion batteries (LIBs), owing to its thermal stability and high ionic conductivity. [1] The structure of LTP consists of TiO₆ octahedra corner-linked to PO₄ tetrahedra, forming a helix about the c-axis. Li⁺ can occupy two sites in the structure: the more stable six-fold O coordinated M1 (6b) and the eight-fold O coordinated M2 (18e), which is less stable. The net ionic movement is described as M1 (6b) - M2 (18e) - M1 (6b). The 3D network allows for the migration of alkali ions through the structure, making the material a candidate as an electrolyte in LIB. However, its room temperature conductivity in the order of 10^-7 S/cm is too low for practical applications in LIBs. [1-2] Lattice site substitutions of Ti⁴⁺with isovalent and aliovalent cations have been proposed to improve ionic conductivity. This is achieved by tuning the tunnel size of Li⁺ in the structure and by altering the energy barriers around the dopant sites for faster Li⁺ migration. Aliovalent cationic substitution significantly improves ionic conductivity by densifying the pelletized material, and because of the high Li content that is introduced for charge balance. [3-4]

In this work, we investigate the effect of Al³⁺;Dy³⁺ substitution at the Ti⁴⁺ site on the room temperature conductivity of LTP. Synchrotron XRD provided insight into the structure, showing that the material under study has a NASICON structure (space group R-3c). Raman spectroscopy and Pair Distribution Function provided information on the changes in local order around the substitution sites as well as confirming the phase composition of the material in question. LADTP showed improved ionic conductivity of 1.28 × 10^-5 S/cm.