High-pressure Single-crystal Synchrotron Research Articles

Accurate crystal structure of ice VI from X-ray diffraction with Hirshfeld atom refinement.

Water is an essential chemical compound for living organisms, and twenty of its different crystal solid forms (ices) are known. Still, there are many fundamental problems with these structures such as establishing the correct positions and thermal motions of hydrogen atoms. The list of ice structures is not yet complete as DFT calculations have suggested the existence of additional and - to date - unknown phases. In many ice structures, neither neutron diffraction nor DFT calculations nor X-ray diffraction methods can easily solve the problem of hydrogen atom disorder or accurately determine their anisotropic displacement parameters (ADPs). Here, accurate crystal structures of H2O, D2O and mixed (50%H2O/50%D2O) ice VI obtained by Hirshfeld atom refinement (HAR) of high-pressure single-crystal synchrotron and laboratory X-ray diffraction data are presented. It was possible to obtain O-H/D bond lengths and ADPs for disordered hydrogen atoms which are in good agreement with the corresponding single-crystal neutron diffraction data. These results show that HAR combined with X-ray diffraction can compete with neutron diffraction in detailed studies of polymorphic forms of ice and crystals of other hydrogen-rich compounds. As neutron diffraction is relatively expensive, requires larger crystals which can be difficult to obtain and access to neutron facilities is restricted, cheaper and more accessible X-ray measurements combined with HAR can facilitate the verification of the existing ice polymorphs and the quest for new ones.

High-pressure single-crystal synchrotron X-ray diffraction study of lillianite

Abstract In this paper, high-pressure data from a synchrotron X-ray diffraction study on a lillianite (Pb3Bi2S6) single crystal up to ~21 GPa are presented. A phase transition from lillianite (space group Bbmm, LP lillianite) to the high-pressure form β-Pb3Bi2S6 (space group Pbnm, HP lillianite) was confirmed and bracketed between 4.90 and 4.92 GPa. The transition is reversible but of first-order with a hysteresis of ~2.8 GPa. It showed weak effects of pseudo-merohedral twinning that disappeared upon decompression, testifying to a full recovery of the single crystal of lillianite. This makes lillianite an interesting shape-memory material. With a bulk modulus K4.9 = 78(3) GPa and K′ = 5.1(4), β-Pb3Bi2S6 is markedly less compressible than lillianite [K0 = 44(2) GPa, K′ = 7(1)]. Compressional anisotropy increases markedly in β-Pb3Bi2S6 with compressibility along the b axis [M0b = 130(6) GPa and Mb′ = 19(3) in lillianite, M4.9b = 145(4) GPa and Mb′ = 16.0(7) in β-Pb3Bi2S6] significantly larger than that along the other two axes [M0a = 118(5) GPa, Ma′ = 21(3), M0c = 139(12) GPa, and Mc′ = 31(10) in lillianite, M4.9a = 242(12) GPa, Ma′ = 8(1), M4.9c = 242(5) GPa, and Mc′ = 29(1) in β-Pb3Bi2S6]. The behavior of lillianite at high pressure is an interesting case study in relation to non-quenchable ultrahigh-pressure phases likely occurring in the inner Earth, like post-perovskite MgSiO3, the oxide homologue N = 1 of the lillianite series. The β-Pb3Bi2S6 structure, on the other hand, is the N = 3 homologue of the meneghinite series to which the higher-pressure modification of the post-perovskite structure also belongs (homologue N = 1). This makes the two forms of Pb3Bi2S6 potential equivalents of high- and ultrahigh-pressure Mg silicates that could occur both in the deep earth and in other rocky extrasolar planetary bodies.

High Pressure Crystal Structure and Electrical Properties of a Single Component Molecular Crystal [Ni(dddt)2] (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate).

Single-component molecular conductors form an important class of materials showing exotic quantum phenomena, owing to the range of behavior they exhibit under physical stimuli. We report the effect of high pressure on the electrical properties and crystal structure of the single-component crystal [Ni(dddt)2] (where dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate). The system is isoelectronic and isostructural with [Pd(dddt)2], which is the first example of a single-component molecular crystal that exhibits nodal line semimetallic behavior under high pressure. Systematic high pressure four-probe electrical resistivity measurements were performed up to 21.6 GPa, using a Diamond Anvil Cell (DAC), and high pressure single crystal synchrotron X-ray diffraction was performed up to 11.2 GPa. We found that [Ni(dddt)2] initially exhibits a decrease of resistivity upon increasing pressure but, unlike [Pd(dddt)2], it shows pressure-independent semiconductivity above 9.5 GPa. This correlates with decreasing changes in the unit cell parameters and intermolecular interactions, most notably the π-π stacking distance within chains of [Ni(dddt)2] molecules. Using first-principles density functional theory (DFT) calculations, based on the experimentally-determined crystal structures, we confirm that the band gap decreases with increasing pressure. Thus, we have been able to rationalize the electrical behavior of [Ni(dddt)2] in the pressure-dependent regime, and suggest possible explanations for its pressure-independent behavior at higher pressures.

The High Pressure Behavior of Galenobismutite, PbBi2S4: A Synchrotron Single Crystal X-ray Diffraction Study

High-pressure single-crystal synchrotron X-ray diffraction data for galenobismutite, PbBi2S4 collected up to 20.9 GPa, were fitted by a third-order Birch-Murnaghan equation of state, as suggested by a FE-fE plot, yielding V0 = 697.4(8) Å3, K0 = 51(1) GPa and K’ = 5.0(2). The axial moduli were M0a = 115(7) GPa and Ma’ = 28(2) for the a axis, M0b = 162(3) GPa and Mb’ = 8(3) for the b axis, M0c = 142(8) GPa and Mc’ = 26(2) for the c axis, with refined values of a0, b0, c0 equal to 11.791(7) Å, 14.540(6) Å 4.076(3) Å, respectively, and a ratio equal to M0a:M0b:M0c = 1.55:1:1.79. The main structural changes on compression were the M2 and M3 (occupied by Bi, Pb) movements toward the centers of their respective trigonal prism bodies and M3 changes towards CN8. The M1 site, occupied solely by Bi, regularizes the octahedral form with CN6. The eccentricities of all cation sites decreased with compression testifying for a decrease in stereochemical expression of lone electron pairs. Galenobismutite is isostructural with calcium ferrite CaFe2O4, the suggested high pressure structure can host Na and Al in the lower mantle. The study indicates that pressure enables the incorporation of other elements in this structure, increasing its potential significance for mantle mineralogy.

High-pressure single-crystal synchrotron X-ray diffraction of kainite (KMg(SO4) Cl 3H2O)

Kainite (KMg(SO4) Cl 3H2O) is a “mixed-salt” sulfate from the group of evaporitic minerals more soluble than Ca-sulfate hydrate and NaCl. The compressibility and structural modifications of monoclinic (sp. gr. C2/m) kainite up to a pressure of 14 GPa were studied by high-pressure single-crystal synchrotron X-ray diffraction. Kainite remains stable over the investigated pressure range and no phase transition was recognised. The bulk modulus is K0 = 31.6 (1) GPa, with K′ fixed to 4, as obtained by fitting the P-volume data with a second-order Birch–Murnaghan EoS (BM2); instead of using a BM3 EoS, we obtained K0 = 32.2(5) GPa, K’ =3.8 (1). The linear moduli calculated for the lattice parameters fitting the data with a BM3 EoS are for a-axis M0a = 117(4) GPa, Mpa = 11(1), for b-axis M0b = 113(2) GPa, Mpc = 8.6(5), and c-axis M0c = 68.2(3) GPa, Mpc = 14(1). Structure refinements showed a strong compression of the K polyhedra and in particular K(1) and K(3) polyhedra have similar polyhedral bulk moduli: K0K(1) = 20.8(7) GPa, K′=4.8(3); K0K(2) = 29(1) GPa, K′=8.1(6); K0K(3) = 26(1) GPa, K′=4.2(4). The most compressible bond distances are K(1)–Cl(2) with a shortening of about 13%, K(1)–Cl(1) with a shortening of about 10%, K(3)–Ow(6) and K(3)–O8(B) both with a shortening of 9%. S-tetrahedra are almost incompressible and Mg-octahedra bulk moduli are K0Mg(2) = 102(4) GPa, and K0Mg(4) = 72(1) GPa, K0Mg(1) = 41(4) GPa K′= 8.9(1.7), and K0Mg(3) = 65(5) GPa K′= 10(2). The strain tensor analysis indicates that the most compressible direction of the kainite monoclinic structure is oriented 29.7(2)° from the c-axis in the (0 1 0) plane. The shortening of the K(1)–K(2) distance (from 4.219(4) A at ambient P to 3.521(7) A at 11.9 GPa) and the different compressibilities of the octahedra/tetrahedra may explain why the stiffer direction of kainite is in the a–c plane approximatively along the direction where K(1)–K(2) and Mg(4)–Mg(3)–Mg(4) polyhedra align. This may explain the anisotropic compressional behaviour of the crystallographic axes, where c is more compressible (by tetrahedral tilting mechanism) than a and b, where cation–cation repulsion and a more rigid configuration make these directions stiffer. Following the structure modification increasing pressure a new sets of hydrogens bonds could form as oxygens and chlorine atoms get at less than 3 A distance from the Ow.

High-pressure single-crystal synchrotron diffraction study of MnGe and related compounds

Single crystal synchrotron diffraction for pressures up to 50 GPa has revealed an essential difference in structural properties and compressibility of MnGe compared with Mn1−xCoxGe and Mn1−xFexGe solid solutions. A negative thermal expansion has been observed for MnGe at low-temperatures and high-pressures. The single crystal refinement has shown a discontinuous change of the atomic coordinates and Mn–Ge interatomic distances of MnGe in contrast to Mn0.1Co0.9Ge. These peculiarities of MnGe are likely to be associated with high-spin–low-spin transition. The relation between anisotropy of the coordination of Mn-atom and its magnetic moment is discussed.

High pressure single-crystal synchrotron X-ray diffraction technique

A lot of great work has been done since the high pressure research carried out on synchrotron radiation facility almost 40 years ago. The history of high pressure single-crystal diffraction research on synchrotron radiation facility has also been more than 20 years. Recently, with the development of synchrotron X-ray optical techniques and high pressure technology, especially the invention and improvement of large opening diamond anvil cell (DAC), high pressure single-crystal X-ray diffraction (HPSXRD) method has become more and more popular in high pressure studies. The HPSXRD can be used to perform structure determination and refinement to obtain the information about lattice parameter, space group, atomic coordinate and site occupation. Compared with powder X-ray diffraction, the HPSXRD can not only obtain the three-dimensional diffraction information of samples, but also have much better signal-to-noise ratio. Furthermore, the HPSXRD data can be used to study the electron density distribution to obtain more information about chemical bonds and electron distribution. In this work, we introduce the HPSXRD method in synchrotron radiation facilities, including the knowledge of single-crystal X-ray diffraction experimental system, DAC for HPSXRD, sample loading, and HPSXRD data processing.

High-pressure behavior of cuprospinel CuFe2O4: Influence of the Jahn-Teller effect on the spinel structure

The Jahn-Teller effect at Cu2+ in cuprospinel CuFe2O4 was investigated using high-pressure single-crystal synchrotron X-ray diffraction techniques at beamline BL10A at the Photon Factory, KEK, Japan. Six data sets were collected in the pressure range from ambient to 5.9 GPa at room temperature. Structural refinements based on the data were performed at 0.0, 1.8, 2.7, and 4.6 GPa. The unit-cell volume of cuprospinel decreases continuously from 590.8(6) to 579.5(8) A3 up to 3.8 GPa. Least-squares fitting to a third-order Birch-Murnaghan equation of state yields the zero-pressure volume V = 590.7(1) A3 and bulk modulus K = 188.1(4.4) GPa with K ′ fixed at 4.0. The structural formula determined by electron microprobe analysis and site occupancy refinement is represented as T (Fe3+0.90Cu2+0.10) M (Fe3+1.10Fe2+0.40Cu2+0.50)O4. Most of the Cu2+ are preferentially distributed onto the octahedrally coordinated ( M ) site of the spinel structure. With pressure, the arrangement of the oxygen atoms around the M cation approaches a regular octahedron. This leads to an increase in the electrostatic repulsion between the coordinating oxygen ions and the 3 d z2 orbital of M Cu2+. At 4.6 GPa, a cubic-tetragonal phase transition is indicated by a splitting of the a axis of the cubic structure into a smaller a axis and a longer c axis, with unit-cell parameters a = 5.882(1) A and c = 8.337(1) A. The tetragonal structure with space group I 41/ amd was refined to R 1 = 0.0332 and wR 2 = 0.0703 using 38 observed reflections. At the M site, the two M -O bonds parallel to the c -axis direction of the unit cell are stretched with respect to the four M -O bonds parallel to the a-b plane, which leads to an elongated octahedron along the c -axis. The cubic-to-tetragonal transition induced by the Jahn-Teller effect at Cu2+ is attributable to this distortion of the CuO6 octahedron and involves Cu 3 d z2 orbital, ab initio quantum chemical calculations support the observation. At the tetrahedrally coordinated ( T ) site, on the other hand, the tetrahedral O- T -O bond angle increases from 109.47° to 111.7(7)°, which generates a compressed tetrahedral geometry along the c -axis. As a result of the competing distortions between the elongated octahedron and the compressed tetrahedron, the a unit-cell parameter is shortened with respect to the c unit-cell parameter, giving a c / a ′ ratio ( ![Formula][1] ) slightly greater than unity as referred to cubic lattice ( c / a ′ = 1.002). The c / a ′ value increases to 1.007 with pressure, suggesting further distortions of the elongated octahedron and compressed tetrahedron. [1]: /embed/mml-math-1.gif

Compressibility and equation of state of beryl (Be3Al2Si6O18) by using a diamond anvil cell and in situ synchrotron X-ray diffraction

High-pressure single-crystal synchrotron X-ray diffraction was carried out on a single crystal of natural beryl compressed in a diamond anvil cell. The pressure-volume (P-V) data from room pressure to 9.51 GPa were fitted by a third-order Birch-Murnaghan equation of state (BM-EoS) and resulted in unit-cell volume V-0 = 675.5 +/- 0.1 angstrom(3), isothermal bulk modulus K-0 = 180 +/- 2 GPa, and its pressure derivative K-0' = 4.2 +/- 0.5. We also calculated V-0 = 675.5 +/- 0.1 angstrom(3) and K-0 = 181 +/- 1GPa with fixed K-0' at 4.0 and then obtained the axial moduli for a (K-a0)-axis and c (K-c0)-axis of 209 +/- 1 and 141 +/- 2 GPa by "linearized" BM-EoS approach. The axial compressibilities of a-axis and c-axis are beta(a) = 1.59 x 10(-3) GPa(-1) and beta(c) = 2.36 x 10(-3) GPa(-1) with an anisotropic ratio of beta(a):beta(c) = 0.67:1.00. On the other hand, the pressure-volume-temperature (P-V-T) EoS of the natural beryl has also been measured at temperatures up to 750 K and at pressures up to 16.81 GPa, using diamond anvil cell in conjunction with in situ synchrotron angle-dispersive powder X-ray diffraction. The P-V data at room temperature and at a pressure range of 0.0001-15.84 GPa were then analyzed by third-order BMEoS and yielded V-0 = 675.3 +/- 0.1 angstrom(3), K-0 = 180 +/- 2 GPa, K-0' = 4.2 +/- 0.3. With K-0' fixed to 4.0, we also obtained V-0 = 675.2 +/- 0.1 angstrom(3) and K-0 = 182 +/- 1 GPa. Consequently, we fitted the P-V-T data with high-temperature BM-EoS approach using the resultant K-0' (4.2) from room-temperature BM-EoS and then obtained the thermoelastic parameters of V-0 = 675.3 +/- 0.2 angstrom(3), K-0 = 180 +/- 1 GPa, temperature derivative of the bulk modulus (partial derivative K/partial derivative T)(P) = -0.01 7 +/- 0.004 GPa K-1, and thermal expansion coefficient at ambient conditions alpha(0) = (2.82 +/- 0.74) x 10(-6) K-1. Present results were also compared with previous studies for beryl. From the comparison of these fittings, we propose to constrain K-0 = 180 GPa and K-0' = 4.2 for beryl. And we also observed that beryl exhibits anisotropic thermal expansion at relatively low temperatures, which is very consistent with previous studies. Furthermore, no phase transition was observed in the entire pressure and temperature range (up to 16.84 GPa and 750 K) of this study for the natural beryl.

The high-pressure behavior of bloedite: A synchrotron single-crystal X-ray diffraction study

High-pressure single-crystal synchrotron X-ray diffraction was carried out on a single crystal of bloedite [Na 2 Mg(SO 4 ) 2 4H 2 O] compressed in a diamond-anvil cell. The volume-pressure data, collected up to 11.2 GPa, were fitted by a second- and a third-order Birch-Murnaghan equation of state (EOS), yielding V 0 = 495.6(7) A 3 with K 0 = 39.9(6) GPa, and V 0 = 496.9(7) A 3 , with K 0 = 36(1) GPa and K ′ = 5.1 (4) GPa −1 , respectively. The axial moduli were calculated using a Birch-Murnaghan EOS truncated at the second order, fixing K ′ equal to 4, for a and b axes and a third-order Birch-Murnaghan EOS for c axis. The results were a 0 = 11.08(1) and K 0 = 56(3) GPa, b 0 = 8.20(2) and K 0 = 43(3) GPa, and c 0 = 5.528(5), K 0 = 40(2) GPa, K ′ = 1.7(3) GPa −1 . The values of the compressibility for a , b , and c axes are β a = 0.0060(3) GPa −1 , β b = 0.0078(5) GPa −1 , β c = 0.0083(4) GPa −1 with an anisotropic ratio of β a :β b :β c = 0.72:0.94:1. The evolution of crystal lattice and geometrical parameters indicates no phase transition up to 11 GPa. Sulfate polyhedra are incompressible, whereas the Mg polyhedral bulk modulus is 95 GPa. The sodium polyhedron is the softest part of the whole structure with a bulk modulus of 41 GPa. Pressure decreases significantly the distortion of Na coordination. Up to 10 GPa, the donor-acceptor oxygen distances decrease significantly and the difference between the two water molecules decreases with an increase in the strengths of hydrogen bonds. At the same time, the bond lengths from Na and Mg to O atoms of the water molecules decrease faster than other bonds to these cations suggesting that there is a coupling between the Na-Ow and Mg-Ow bond strengths and the “hydrogen transfer” to acceptor O atoms.