A new approach to time-resolved X-Ray experiments implementation at both laboratory X-Ray sources and synchrotron facilities is presented. Proposed X-Ray diffraction method is based on adaptive X-ray optics and applied for investigation of irreversible deformation processes in crystalline materials under external loading with time resolution. This method allows receiving information about changes in atomic structure recording rocking curves (dependence of X-ray radiation intensity in the vicinity of Bragg angle) and reciprocal space maps (RSM) by fast tunable X-Ray optical element. This element consists of a piezoelectric monolithic bimorph lithium niobate (LiNbO3) single crystal and a silicon plate attached to its face. When electrical signal is applied to the lithium niobate, it is possible to control the spatial position of the diffracted X-ray beam [1]. Time resolution of proposed method scales up to milliseconds for rocking curve record and up to hundreds of milliseconds in RSM case, and mainly depending on brilliance of X-ray.

The presented approach makes it possible to obtain information about changes in crystal structure with a lower time delay compared to existing methods [2].

The evolution of the defective structure of crystalline materials subjected to controllable and measured uniaxial mechanical compression (load up to MPa range) was investigated using the proposed method. The essence of such evolution is defect multiplication, displacement and shifting of atomic planes, which can be easily determined by changes in rocking curve and RSM parameters. This structural process is of great interest, as it is possible to observe defects behavior in a crystal during elastic deformation with time resolution.

The reported study was funded by RFBR and DFG 19-52-12029 and by RFBR according to the research project №18-32-20108.

Transition metal oxides with the perovskite crystal structure constitute a class of materials long considered highly interesting for research in structure-property relationships and materials design. In this work we consider the B cation rock salt ordered double perovskite structure, with general formula A₂BB´O₆. We are interested in the magnetically frustrated fcc B’ cation sublattice, where on the B´ position we have placed Rh 4d⁵ as a reduced SOC analogue in the context of our previous iridate double perovskite work.

We have synthesized La₂BRhO₆ (B = Zn, Mg) compounds as powders and single crystals that form in the P2₁/n space group. Their structure and properties have been characterized with a combination of XRD, SQUID magnetometry, and heat capacity. Interestingly, the materials exhibit no long range order to very low temperatures, and may host an exotic magnetic ground state.

Metal-organic frameworks (MOFs) are an emerging class of crystalline materials made by connecting a metal ion or cluster to polytypic organic linkers. They have a wide range of potential applications in gas storage, catalysis, drug delivery, sensing, separation, and magnetism [1, 2]. Single crystal to single crystal (SC-SC) transformation is a phenomenon where significant changes in the crystal structure occur in the solid state without destroying the integrity of the crystal such that it can still be analyzed by means of X-ray diffraction. Single crystal transformations are important for the development of new and technologically useful materials including devices and sensors.

Recently, we synthesized the MOF, {[Co(34pba)₂(OH₂)](DMF)_0.5(H₂O)}_n (A)_, DMF= N,N-dimethylformamide, 34pba= with water and DMA using solvothermal method. X-ray analysis revealed that A crystallises in the Triclinic, system with space group of P-1. Further studies revealed that A is a dynamic material which can be used for sensing [3].

In this work, we present the solid state studies in A and DMF using solvothermal methods. They were fully characterized using X-ray diffraction methods, infrared spectroscopy, elemental analysis and thermal methods.

[1] Kuppler R., Timmons D., Fang Q., Li J., Makal T., Young M., Yuan D., Zhao D., Zhuang W., Zhou H., (2009), Coord. Chem. Rev., 253, 3042

[2] Farha O. and Hupp J., (2010), Accounts of Chem. Rese., 43, 1166

[3] Dzesse Tekouo. C. N., Emmanuel N. Nfor and Susan A. Bourne,( 2018), Crystal growth & Des., , 18(1), 416.

Square planar rhodium(I) complexes of the type [Rh(L,L’-Bid)(CO)(PPX₃)], where L,L’-Bid = monoanionic bidentate ligands and PPX₃ are tertiary phosphine ligands, have been extensively investigated as potential catalyst precursors in different conversion reactions. ^{[1],[2],[3],[4],[5]}

The main objective of this study is to use solution and solid-state ³¹P NMR spectroscopy in conjunction with X-ray crystallography to investigate the structure and reactivity relationship of the rhodium(I) complexes for potential application in catalysis.

A range of complexes of the type [Rh(L, L’-Bid)(CO)(PPX₃)] with systematic manipulation of the steric and electronic properties were synthesized and characterized using IR, UV/Vis, and NMR spectroscopy. These rhodium(I) complexes were obtained from the substitution of one carbonyl ligand in the complexes [Rh(L,L’-Bid)(CO)₂], by simple stoichiometric reaction with monodentate tertiary phosphines. Correlations of different parameters such as the first-order coupling constant ¹J_Rh-P, chemical shift, and the Rh-P bond distances were evaluated in order to understand the coordination environment around the metal center.

[1] A. Roodt, H.G. Visser, A. Brink. Crystallogr. Rev. 17 (2011) 241-280.

[2] S. Warsink, F.G. Fessha, W. Purcell, J.A. Venter, J. Organomet. Chem. 726 (2013) 14-20.

[3] M. M. Conradie, J. Conradie, Dalton Trans. 40 (2011) 8226-8237.

[4] A. Brink, A. Roodt, G. Steyl, H.G. Visser, Dalton Trans. 39 (2010) 5572–5578.

^[5] P.P Mokolokolo, A. Brink, M. Schutte-Smith, A. Roodt. J. Coord. Chem. 73 (2020) 2740.

A new metal pyrophosphate, formulated as [(H₂O)₂Co₂(N₂H₅)₂(HP₂O₇)₂] has been synthesized using wet chemistry and investigated by single crystal X-ray diffraction. The compound crystallizes in the triclinic system (S.G: P) with the following parameters (Å, °): a=7.2957(6), b=7.3932(4), c=14.7194(8), α=85.717(4), β=83.703(6), γ=79.710(5). The crystal packing consists of layers parallel to bc plane. These layers are joined by strong hydrogen bonds, building up a three-dimensional infinite network. The structural analysis was coupled with Hirshfeld surface analysis to evaluate the contribution of the different intermolecular interactions to the formation of supramolecular assemblies in the solid state. This analysis revels that the main contributions are provided by the O···H, H···H and Co···O interactions that represent ~85% of the total contributions to the Hirshfeld surface. Pyrophosphate group show bent eclipsed conformation which was confirmed by IR spectroscopy. Its Thermal behaviour consists mainly of the loss of hydrazine moieties and water molecules leading thus to the formation of an anhydrous cobalt diphosphate. The condensed phosphate exhibits a promising catalytic activity in the oxidation and decomposition of methylene blue dye with hydrogen peroxide under ambient conditions only for 2 hours.

Currently, a significant area of materials science concerns the development of mechanisms for controlled variation of a material’s structure through local defects formation. This ensures the adjustment of a material’s structural organization and functional properties for application in novel data storages, sensors, and energy accumulation systems, among others.

The near-surface structural variation has been found in SrTiO₃ [1] and in TeO₂ single crystals as well. It is caused by the migration of oxygen vacancies in an external electric field. The dynamics and anisotropy of the formation process of near-surface structures in paratellurite (α-TeO₂) single crystals due to the migration of charge carriers induced by an external electric field are studied by the in-situ X-ray diffraction (XRD) technique and electrical conductivity measurements.

Single crystal diffraction patterns exhibit an interesting response on an external electric field. The observed effect manifests itself in the diffraction rocking curve (DRC) parameters and its shape variation with a reversible character [2]. This is explained by the formation of the strain field (domains) with a small mutual angular misorientation. The threshold field strength about 100 V/mm, above which the broadening of the XRD reflection peak starts, has been revealed. A linear dependence of the broadening value on the applied field strength has been determined.

A diffraction peak broadening occurs for both polarities with a simultaneous shift of its maximum only occurring on the surface with a positive electric potential [3]. For the (110) crystal cut, a much higher saturation time (800-1000 s) of the process compared to the (100) cut (~300 s) is registered. Moreover, in all cases, the relaxation is almost 2–3 times faster than the saturation, thereby repeating the character of the measured electrical conductivity. The electric field application along the fourth-order axis [001] doesn’t lead to visible changes in the diffraction peak parameters.

A thickness of the layer with a strain formed close to the surface is estimated by XRD at different diffraction orders [4]. The experimental data is compared with the results of DRC simulation considering the crystal lattice deformation with the depth attenuation. The simulation shows the strain localization depth of 3.6 μm for the (110) crystallographic cut, whereas the diffraction peak profile for the (100) cut is suitably described by a layer with a thickness of 1.6 μm.

Calculation according to the electrical measurements shows that the Debye screening layer of charge is localized at the same characteristic length. The concentration of defects in the near-surface region is inversely dependent on the screening length and reaches the value of 1.3×10²² m⁻³, which is three orders of magnitude greater than vacancies concentration in the bulk.

[1] Hanzig, J., Zschornak, M., Hanzig, F., Mehner, E., Stöcker, H., Abendroth, B., Röder, C., Talkenberger, A., Schreiber, G., Rafaja, D., Gemming, S., & Meyer D. C. (2013). Physical Review B 88, 024104.
[2] Kovalchuk, M. V., Blagov, A. E., Kulikov, A. G., Marchenkov, N. V. & Pisarevsky, Yu. V. (2014). Crystallography Reports 59(6), 862.
[3] Kulikov, A. G., Blagov, A. E., Marchenkov, N. V., Lomonov, V. A., Vinogradov, A. V., Pisarevsky, Yu. V. & Kovalchuk, M. V. (2018). JETP Letters 107(10), 646.
[4] Kulikov, A. G., Blagov, A. E., Ilin, A. S., Marchenkov, N. V., Pisarevsky, Yu. V. & Kovalchuk, M. V. (2020). Journal of Applied Physics 127, 065106.

Keywords: near-surface structure; electrical double layer; charge carriers’ migration; X-ray diffractometry

This work supported by the Ministry of Science and Higher Education within the State assignment FSRC Crystallography and Photonics RAS in part of “crystal growth and sample preparation” and by the Russian Foundation for Basic Research (Project No. 19-52-12029 NNIO_a), part of “investigation of the paratellurite crystal structure rearrangement under the electric field influence”.

Mechanically responsive organic materials have attracted attention from perspective of both basic research and applications in smart actuators and soft robots [1]. We have developed many mechanical crystals such as azobenzene [2] and salicylidenealine [3], mainly based on photoisomerization. However, photoisomerization has some disadvantages for crystal actuation, such as a limited number of photoisomerizable crystals, slow actuation speed, and no actuation of thick crystals. Here we report photothermally driven fast-bending actuation and simulation of a salicylideneaniline derivative crystal with an o-amino substituent in enol form (enol-1).

X-ray crystallographic analysis revealed that enol-1 crystal belonged to the space group, P2₁, showing that the enol-1 molecule is achiral but forms chiral crystal. The molecules were connected weakly through the intermolecular hydrogen bond chains in a two-fold helical manner to form the herringbone structure along the b axis (Figure 1a, b). Absorption spectra of a thin enol-1 crystal revealed that enol-1 crystal exhibited fast photoisomerization from enol to trans-keto form (τ=0.9 s) by UV light and fast back-isomerization (τ=4.2 s) from trans-keto to enol form.

Under UV light irradiation, the thin (<20μm) crystals bent away from the light source quickly (in a few seconds) by photoisomerization. In contrast, the thick (>20μm) crystals bent very quickly (in several milliseconds) due to the photothermal effect, finally achieving 500-Hz high-frequency bending by pulsed UV laser irradiation. We propose a possible mechanism in which photothermally driven bending is caused by a non-steady temperature gradient in the thickness direction. The temperature gradient was calculated based on a one-dimensional non-steady heat conduction equation, resulting in the successful simulation of bending via the photothermal effect and the elucidation of the proposed mechanism (Figure 1c). Most materials that absorb light show their own photo-thermal effects. The creation of crystal motion via the photothermal effect will expand the designability and versatility of mechanical crystals in the future.

[1] Koshima, H. (2020). Mechanically Responsive Materials for Soft Robotics, ed. H. Koshima, Wiley-VCH, Weinheim.

[2] Koshima, H., Ojima, N., Uchimoto, H. (2009). J. Am. Chem. Soc. 131, 6890–6891.

[3] Koshima, H., Takechi, K., Uchimoto, H., Shiro, M., Hashizume, D. (2011). Chem. Commun. 47, 11423–11425.