Single-crystal Synchrotron X-ray Diffraction Research Articles

High-pressure synthesis of rhenium carbide Re3C under megabar compression

The rhenium carbide Re3C was predicted to be stable under high pressure and expected to have high hardness and low compressibility. In this study, we realise the synthesis of Re3C at megabar pressures of 105(3) and 140(5) GPa in laser-heated diamond anvil cells and characterise its structure using synchrotron single-crystal X-ray diffraction. The structure of Re3C has the monoclinic space group C2/m and is built of CRe7 capped octahedra. Our combined ab initio calculations and quantitative topological analysis support experimental structural data and further deepen the understanding of the chemical bonding in the newly synthesized compound.

Influence of cation disorder on the mineral physics of ankerite

Abstract The structural evolution and compressibility of ordered and disordered ankerite at pressures up to ~25 GPa using synchrotron single crystal X-ray diffraction in diamond anvil cell was analyzed. Ordered ankerite (space group R3) undergoes discontinuous phase transition between 12.15 and 13.45 GPa to a high-pressure structure called ankerite-II (space group P1) that has Ca in eight-fold coordination. Disordered ankerite (R3c space group) does not undergo a phase transition in the investigated pressure range. A Birch-Murnaghan equation of state has been used to fit the volume compressibility. Ordered ankerite [K0V=95(1) GPa - K’=3.8(3)] appears slightly more compressible than disordered ankerite [K0V=99(1) GPa - K’=2.7(1)]. The phase transition in ordered ankerite has a change in volume of approximately 0.6% and K13.45V=110(11) GPa - K’=7(3) for ankerite-II. The possible significance of this differential behavior of ordered and disordered ankerite is discussed.

Single-Crystalline 3D Covalent Organic Frameworks with Exceptionally High Specific Surface Areas and Gas Storage Capacities.

Single-crystalline covalent organic frameworks (COFs) are highly desirable toward understanding their pore chemistry and functions. Herein, two 50-100 μm single-crystalline three-dimensional (3D) COFs, TAM-TFPB-COF and TAPB-TFS-COF, were prepared from the condensation of 4,4',4″,4‴-methanetetrayltetraaniline (TAM) with 3,3',5,5'-tetrakis(4-formylphenyl)bimesityl (TFPB) and 3,3',5,5'-tetrakis(4-aminophenyl)bimesityl (TAPB) with 4,4',4″,4‴-silanetetrayltetrabenzaldehyde (TFS), respectively, in 1,4-dioxane under the catalysis of acetic acid. Single-crystal 3D electron diffraction reveals the triply interpenetrated dia-b networks of TAM-TFPB-COF with atom resolution, while the isostructure of TAPB-TFS-COF was disclosed by synchrotron single-crystal X-ray diffraction and synchrotron powder X-ray diffraction with Le Bail refinements. The nitrogen sorption measurements at 77 K disclose the microporosity nature of both activated COFs with their exceptionally high Brunauer-Emmett-Teller surface areas of 3533 and 4107 m2 g-1, representing the thus far record high specific surface area among imine-bonded COFs. This enables the activated COFs to exhibit also the record high methane uptake capacities up to 28.9 wt % (570 cm3 g-1) at 25 °C and 200 bar among all COFs reported thus far. This work not only presents the structures of two single-crystalline COFs with exceptional microporosity but also provides an example of atom engineering to adjust permanent microporous structures for methane storage.

Polytypism of incommensurately modulated structures of crystalline bromine upon molecular dissociation under high pressure

Polytypism of incommensurately modulated structures was hitherto unobserved. Here, it was found in solid bromine and iodine upon molecular dissociation under pressure up to 112 GPa. Single-crystal synchrotron x-ray diffraction in laser-heated diamond anvil cells revealed a number of allotropes of bromine and iodine, including polytypes of Br-IIIγ (Fmmm(00γ)s00) with γ varying within 0.18 to 0.3, coexisting at a given pressure. This finding opens a research area in the field of solid-solid phase transitions, disordered states of solid matter, and high-pressure structural studies. Published by the American Physical Society 2024

Polymorphism of pyrene on compression to 35 GPa in a diamond anvil cell

Structural studies of pyrene have been limited to below 2 GPa. Here, we report on investigations of pyrene up to ~35 GPa using in situ single-crystal synchrotron X-ray diffraction in diamond anvil cells and ab initio calculations. They reveal the phase transitions from pyrene-I to pyrene-II (0.7 GPa), and to the previously unreported pyrene-IV (2.7 GPa), and pyrene-V (7.3 GPa). The structure and bonding analysis shows that gradual compression results in continuous compaction of molecular packing, eventually leading to curvature of molecules, which has never been observed before. Large organic molecules exhibit unexpectedly high conformational flexibility preserving pyrene-V up to 35 GPa. Ab initio calculations suggest that the phases we found are thermodynamically metastable compared to pyrene-III previously reported at 0.3 and 0.5 GPa. Our study contributes to the fundamental understanding of the polymorphism of polycyclic aromatic hydrocarbons and calls for further theoretical exploration of their structure–property relationships.

Synthesis and crystal structure of acentric anhydrous beryllium carbonate Be(CO3).

The anhydrous alkaline earth metal carbonate Be(CO3) was synthesized in a laser-heated diamond anvil cell at moderate pressures and temperatures (20(2) GPa and 1500(200) K) by a reaction of BeO with CO2. It crystallizes in the acentric, trigonal space group P3121 with Z = 3. The crystal structure was obtained from synchrotron single crystal X-ray diffraction data and confirmed by density functional theory-based calculations in combination with Raman spectroscopy. Second harmonic generation measurements were employed to verify the acentric space group symmetry. The crystal structure of Be(CO3) is characterized by the presence of isolated [CO3]2--groups and BeO4-tetrahedra. This is a new structure type and such a topology has not been observed in carbonates before. Be(CO3) can be recovered to ambient conditions and is not undergoing a phase transition during decompression.

Dense Hydrated Magnesium Carbonate MgCO3·3H2O Phases.

The study of the structural stability of carbonates under different pressure and temperature conditions is important for modeling the carbon budget in the Earth's interior and the stability of carbonation products of carbon capture and storage (CCS) solutions. In this work, we confirm the existence of the two dense polymorphs of the hydrated magnesium carbonate MgCO3·3H2O nesquehonite mineral previously reported, and we characterize their structures using synchrotron single-crystal X-ray diffraction at 3.1 and 11.6 GPa. Phase transitions entail the distortion and atomic rearrangement of the Mg-centered polyhedra and the tilting of the [CO3] carbonate units. In particular, the Mg coordination number increases from 6 in nesquehonite to 7 in the second high-pressure phase, while maintaining a topology based on complex MgCO3(H2O)2 chains. We also studied their vibrational behavior upon compression using Raman spectroscopy and complemented the experimental results with density-functional theory (DFT) calculations. The role played by hydrogen bonds in the compressibility and the polymorphism of this hydrated carbonate is also discussed.

High-Pressure oC16-YBr3 Polymorph Recoverable to Ambient Conditions: From 3D Framework to Layered Material.

Exfoliation of graphite and the discovery of the unique properties of graphene─graphite's single layer─have raised significant attention to layered compounds as potential precursors to 2D materials with applications in optoelectronics, spintronics, sensors, and solar cells. In this work, a new orthorhombic polymorph of yttrium bromide, oC16-YBr3 was synthesized from yttrium and CBr4 in a laser-heated diamond anvil cell at 45 GPa and 3000 K. The structure of oC16-YBr3 was solved and refined using in situ synchrotron single-crystal X-ray diffraction. At high pressure, it can be described as a 3D framework of YBr9 polyhedra, but upon decompression below 15 GPa, the structure motif changes to layered, with layers comprising edge-sharing YBr8 polyhedra weakly bonded by van der Waals interactions. The layered oC16-YBr3 material can be recovered to ambient conditions, and according to Perdew-Burke-Ernzerhof-density functional theory calculations, it exhibits semiconductor properties with a band gap that is highly sensitive to pressure. This polymorph possesses a low exfoliation energy of 0.30 J/m2. Our results expand the list of layered trivalent rare-earth metal halides and provide insights into how high pressure alters their structural motifs and physical properties.

Compressibility and pressure-induced structural evolution of kokchetavite, hexagonal polymorph of KAlSi3O8, by single-crystal X-ray diffraction

Abstract Compressibility and pressure-induced structural evolution of kokchetavite, the hexagonal polymorph of KAlSi3O8, has been studied up to 11.8 GPa using synchrotron single-crystal X-ray diffraction. Two phase transitions were observed at pressures of ~0.3 and 10.4 GPa. Kokchetavite-I (as-synthesized, P6/mcc) transforms into kokchetavite-II with the P6c2 space group. Kokchetavite-II → kokchetavite-III phase transition at ~10.4 GPa is accompanied by a change of symmetry to probably orthorhombic. After pressure release, kokchetavite reverts to the initial single-crystal state with P6/mcc space group. A second-order Birch-Murnaghan equation of state was calculated for phase kokchetavite-II with coefficients V0 = 1486(3) Å3, K0 = 59(2) GPa.

Phonon softening and atomic modulations in EuAl4

EuAl4 is a rare-earth intermetallic in which competing itinerant and/or indirect exchange mechanisms give rise to a complex magnetic phase diagram, including a centrosymmetric skyrmion lattice. These phenomena arise not in the tetragonal parent structure but in the presence of a charge-density wave (CDW), which lowers the crystal symmetry and renormalizes the electronic structure. Microscopic knowledge of the corresponding atomic modulations and their driving mechanism is a prerequisite for a deeper understanding of the resulting equilibrium of electronic correlations and how it might be manipulated. Here, we use synchrotron single-crystal x-ray diffraction, inelastic x-ray scattering, and lattice-dynamics calculations to clarify the origin of the CDW in EuAl4. We observe a broad softening of a transverse acoustic phonon mode that sets in well above room temperature and, at TCDW=142 K, freezes out in an atomic displacement mode described by the superspace group Immm(00γ)s00. In the context of previous work, our observation is a clear confirmation that the CDW in EuAl4 is driven by electron-phonon coupling. This result is relevant for a wider family of BaAl4 and ThCr2Si2-type rare-earth intermetallics known to combine CDW instabilities and complex magnetism. Published by the American Physical Society 2024

High-pressure dysprosium carbides containing carbon dimers, trimers, chains, and ribbons

Exploring the chemistry of materials at high pressure leads to discoveries of previously unknown compounds and phenomena. Here chemical reactions between elemental dysprosium and carbon were studied in laser-heated diamond anvil cells at pressures up to 95 GPa and temperatures of ∼2800 K. In situ single-crystal synchrotron X-ray diffraction (SCXRD) analysis of the reaction products revealed the formation of novel dysprosium carbides, γ-DyC2, Dy5C9, and γ-Dy4C5, along with previously reported Dy3C2 and Dy4C3. The crystal structures of γ-DyC2 and Dy5C9 feature infinite flat carbon polyacene-like ribbons and cis-polyacetylene-type chains, respectively. In the structure of γ-Dy4C5, carbon atoms form dimers and non-linear trimers. Dy3C2 contains ethanide-type carbon dumbbells, and Dy4C3 is methanide featuring single carbon atoms. Density functional theory calculations reproduce well the crystal structures of high-pressure dysprosium carbides and reveal conjugated π-electron systems in novel infinite carbon polyanions. This work demonstrates that complex carbon homoatomic species previously unknown in organic chemistry can be synthesized at high pressures by direct reactions of carbon with metals.

High-Pressure Synthesis of the Iodide Carbonate Na5(CO3)2I

Here, we present the synthesis of a novel quaternary compound, iodide carbonate Na5(CO3)2I, at 18(1) and 25.1(5) GPa in laser-heated diamond anvil cells. Single-crystal synchrotron X-ray diffraction provides accurate structural data for Na5(CO3)2I and shows that the structure of the material can be described as built of INa8 square prisms, distorted NaO6 octahedra, and trigonal planar CO32− units. Decompression experiments show that the novel iodide carbonate is recoverable in the N2 atmosphere to ambient conditions. Our ab initio calculations agree well with the experimental structural data, provide the equation of state, and shed light on the chemical bonding and electronic properties of the new compound.

Multiscale structure of LaAlO3 from single-crystal X-ray diffraction.

A domain-resolved synchrotron single-crystal X-ray diffraction study of a LaAlO3 pseudo-merohedral twin crystal was successfully carried out in combination with powder diffraction data from the same sample. Multiscale structure information ranging from micro- to nano- to atomic scale was determined from one single crystal. There is almost no change of domain ratios at temperatures of less than 400 K indicating no movement of the domain wall. The changes in domain ratio indicating domain-wall movement were observed in the temperature range of 450 to 700 K, which is consistent with the result of the previous mechanical measurement. It is also found that the ratio of four twin components becomes equal (25%), just below phase transition temperature. These findings are important for domain engineering and theoretical studies related to LaAlO3. The temperature dependence of domain ratio was preserved in the heating and cooling cycle except for the first heating process to 840 K. Therefore, the domain structure after heating to 840 K is intrinsic to the crystal. Accurate structure parameters were determined through unit-cell parameter calibration and domain-resolved structure analysis. The method for calibration of unit-cell parameters from twin crystal data was derived and used to solve the inconsistent unit-cell parameters between single crystal and powder data in the present and previous studies.

Toward an understanding of the role of structural organization and point defects in the formation of functional pure and Tm3+-doped (Ca3-xSrx)(VO4)2 for diode-pumped and SRS lasers

Whitlockite-type polycrystalline and single-crystal (Ca3−xSrx)(VO4)2 solid solutions were successfully obtained by solid-state synthesis and Czochralski method, respectively. Synchrotron powder X-ray diffraction allowed to reveal actual compositions of polycrystalline (Ca3−xSrx)(VO4)2 solid solutions with х = 0.3, 0.54, 0.9, 1.2, 1.35 refined by Rietveld method, which are slightly different from the initial ones. Synchrotron X-ray single-crystal diffraction analysis of Czochralski-grown undoped (Ca1.8Sr1.2)(VO4)2 (CSVO) revealed its actual composition (Ca2.982(11)Sr0.031)(VО4)2. Difference between initial and refined compositions is analyzed and discussed. In the CSVO structure, Sr2+ ions partially occupy monocapped Ca2 and two-capped Ca3 trigonal prismatic sites and Ca2+ ions are in the Ca5 and Ca5A sites, forming two independent strongly distorted tetrahedral Ca5O4 and octahedral Ca5AO6 oxygen environments. Synchrotron X-ray single-crystal diffraction analysis together with X-ray absorption spectroscopic study of (Сa2.4Sr0.6)(VO4)2 doped with 0.5 and 1.0 wt% Tm2O3 (СSVO:0.5Tm and CSVO:1.0Tm) allowed to establish the absence of cations in the Ca5A site, the localization of Sr2+ ions in the Ca2 and Ca3 sites and additionally in octahedral Ca4 site together with Tm3+ ions, forming an individual eight-coordinated environment, in the refined compositions (Ca2.776(7)Sr0.210(4)Tm3+0.008(1))(VO4)2 and (Ca2.855(7)Sr0.140(7)Tm3+0.009(1)□0.022(7))(VO4)2, respectively, with vacancies (marked by a square,□) in the two-capped Ca1 trigonal prismatic site in the CSVO:1.0Tm structure. Additional interstitial oxygen, participating in the formation of the Tm3+ environment, found in the residual electron density, together with vacancies in the Ca1 site provides electroneutrality to CSVO:0.5Tm and CSVO:1.0Tm crystals. Several structural models of the coordination environment of Tm3+ ions were analyzed and the most correct one was proposed.

Diffusion dominant thermal transport in mixed valent Ba4Sn4Se9

New material developments are of paramount importance from the perspective of developing a fundamental understanding of material properties as well as transitioning from materials to devices. Among the different classes of materials of interest, mixed valence Sn compositions have been known to display technologically important properties and are of interest for the design and synthesis of novel compositions for targeted applications. Herein, we report on electronic, optical and thermal properties of the previously unexplored mixed valence composition Ba4Sn4Se9, a material with a direct optical band gap of 2.36 eV. As revealed by single crystal synchrotron X-ray diffraction, Ba4Sn4Se9 crystallizes in the orthorhombic space group Pnma with a large unit cell comprised of 58 atoms. Heat capacity data reveals a low Debye temperature with many low frequency optic modes. Our low temperature thermal conductivity data and analyses show that thermal diffusion dominates thermal transport above 80 K. Furthermore, high lattice anharmonicity contributes to the very low thermal conductivity. Our results and analyses will motivate further investigations of this as well as other compositions in the Ba-Sn-Se system, as well as other mixed valence chalcogenides for technological applications.

Electron density changes accompanying high-pressure phase transition in AlOOH

Abstract An attempt to compare and describe the differences in the electron density distribution between two phase structures of AlOOH has been made. High-resolution, high-pressure experiments with α-AlOOH diaspore were conducted using single-crystal synchrotron X-ray diffraction data. A multipole model of experimental electron density in the α-AlOOH single crystal was refined. Simultaneously, similar multipole refinement was conducted for another phase of diaspore (δ-AlOOH), this time based on a previously published data set. Both results were compared and supported by density functional theory (DFT) calculations. Although the results are affected by the limited quality of the data, it is clear that the phase transition caused significant changes in the shape and arrangement of the atomic basins. Atomic basins are a much better tool to present subtle electron density distribution changes than traditional polyhedra. Straightforward comparison of datasets available in older scientific papers and current datasets is challenging because of differences in data quality and collection parameters. However, augmenting experimental data with computational results can help reveal important information in even incomplete datasets.

Electromechanical properties of uniaxial polar ionic plastic crystal [(C2H5)4N][FeBrCl3

Abstract Ferroelectric plastic crystals are an emerging class of materials that combine room temperature ferroelectricity and piezoelectricity with a high temperature plastic mesophase prior to melting. These materials offer possibilities for accessing different property parameter spaces from the state-of-the-art metal oxide and polymer ferroelectrics. Tetraethylammonium bromotrichloroferrite, [(C2H5)4N][FeBrCl3], has a unipolar wurtzite-like structure and thus may have potential for small but stable piezoelectric coefficients like the iso-symmetrical AlN. In this study, density functional theory was used to compute elastic compliance, piezoelectric coefficients, and dielectric constant values. Single crystals grown from aqueous solutions were evaluated via single crystal synchrotron x-ray diffraction, impedance spectroscopy and high and weak-field electromechanical characterization. Diffraction studies revealed that the anion tetrahedra orientated preferentially so that the Br− ion had a 30% alignment with the polarization vector. Electromechanical measurements found piezoelectric coefficients in the 5–9 pC N−1 and pm V−1 range. The piezoelectric coefficient (d 33) was most stable with 3.4% variation between 0.4 and 90 Hz and 0.5 and 3 V. Additional piezoelectric stability measurements were made as a function of DC bias field and temperature. Impedance measurements indicate contributions from either intrinsic effects unique to ionic plastic crystals, such as molecular rotation, or the extrinsic effect of electrode interfaces, both of which can play a role in the electromechanical response of the materials. The results show that [(C2H5)4N][FeBrCl3] has potential as a small signal piezoelectric that has a softer elastic moduli than AlN but a stiffer moduli than polyvinylidene fluoride, and thus occupies a unique parameter space.

Unexpected formation of FeIIFeIIIFeII- and FeIIFeIIFeII-trinuclear hexapyridineoximate helicates: synchrotron single-crystal X-ray structures

Template condensation of 2-acetylpyridineoxime with butyl ester of 1,3-propanediboronic acid in the presence of iron(II) affords a poorly separable mixture of complex products. Similar results were observed when Fe3+ ions were used for cross-linking in place of the diboronic acid. Prolonged crystallization of these mixtures gave crystals of perchlorate salts of a FeIIFeIIIFeII-trinuclear hexapyridineoximate cation and of an analogous FeIIFeIIFeII-intracomplex that crystallize with chloroform and dichloromethane solvent molecules, respectively. Both complexes were characterized by synchrotron single-crystal X-ray diffraction (XRD) experiments. The Fe–N distances of the two ‘terminal’ iron cations are virtually the same between these trinuclear complexes and unambiguously support assignments of oxidation number +2 and low-spin state (S = 0). The centers of the FeN6 -coordination polyhedra adopt geometries resembling trigonal antiprisms with distortion angles φ of approximately 40°. The FeO6 -coordination polyhedra possess an almost ideal Oh geometry with φ close to 60°. Each of these iron(II) or iron(III) µ3 -metallocenters acts as a bifunctional Lewis acid that cross-links two pseudoclathrochelate entities, formed by the ‘terminal’ iron(II) ions, to give an almost linear (the corresponding intramolecular Fe(2)…Fe(1)…Fe(3) angles are close to 180°) helical cation or intracomplex.

Diverse high-pressure chemistry in Y-NH3BH3 and Y-paraffin oil systems.

The yttrium-hydrogen system has gained attention because of near-ambient temperature superconductivity reports in yttrium hydrides at high pressures. We conducted a study using synchrotron single-crystal x-ray diffraction (SCXRD) at 87 to 171 GPa, resulting in the discovery of known (two YH3 phases) and five previously unknown yttrium hydrides. These were synthesized in diamond anvil cells by laser heating yttrium with hydrogen-rich precursors-ammonia borane or paraffin oil. The arrangements of yttrium atoms in the crystal structures of new phases were determined on the basis of SCXRD, and the hydrogen content estimations based on empirical relations and ab initio calculations revealed the following compounds: Y3H11, Y2H9, Y4H23, Y13H75, and Y4H25. The study also uncovered a carbide (YC2) and two yttrium allotropes. Complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, as revealed by ab initio calculations, underline the challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials.

Dehydration kinetics of nanoconfined water in beryl probed by high temperature single crystal synchrotron X-ray diffraction

Understanding changes in material properties through external stimuli plays a key role in validating the expected performance of materials and engineering material properties in a controlled manner. Here, we introduce a fundamental protocol to deduce dehydration reactions kinetics of water confined in nanopore channels, with the cyclosilicate beryl as the scaffold of interest, using time-resolved synchrotron X-ray diffraction (SXRD), in the temperature interval of 298–1038 K. The temperature-dependent intensity (I)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(I)$$\\end{document} of the strongest reflection (112) was used as the crystallite variable. An estimation of an isobaric thermal crystallite coefficient, k\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k$$\\end{document}, analogous with the isobaric thermal expansion coefficient, established the rate of relative crystallization as a function of temperature, ∂I∂T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{\\partial I}{\\partial T}$$\\end{document}. A plot of lnk\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$lnk$$\\end{document} and 1T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\frac{1}{T}$$\\end{document} gives rise to two kinetic steps, indicating a slow dehydration stage up to ~ 700 K and a fast dehydration stage up to the investigated temperature 1038 K. The crystal structure of beryl determined up to 1038 K, in temperature increment as small as 10 K, indicates the presence of channel ions Na and Fe and a gradual decrease of water upon heating.