High-pressure X-ray Diffraction Study Research Articles

Photo-induced structural transformations in crystals at high pressure. Part 1. The crystallographic studies of the photochemical reaction at high pressure

Abstract The preliminary results of high-pressure X-ray diffraction studies of the intramolecular photochemical Norrish–Yang reaction in single crystals of the salt of 6,6-diethyl-5-oxo-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid and (1S)-1-(4-methylphenyl)ethylamine are presented. The photo-induced changes in the cell parameters at high pressure along with the time of UV irradiation and the changes in the cell parameters along with pressure are discussed. The percentage change in the cell parameters brought about by the photochemical reaction at high pressure is similar to that at normal pressure. The cell volume decreases non-linearly with increasing pressure. The crystals lose their crystallinity above 2 GPa. This is the first paper in scientific literature on monitoring photochemical reactions in crystals at high pressure by X-ray diffraction.

High-Pressure Raman and X-ray Diffraction Study of β- and γ-Polymorphs of Aluminum Hydride

Three polymorphs of alane, AlH3, (α, β, and γ) were synthesized and studied at high-pressure in diamond anvil cell by Raman spectroscopy and synchrotron X-ray diffraction. According to synchrotron X-ray diffraction study, β-AlH3 is stable up to 6 GPa, followed by transformation into α phase at higher pressures. X-ray-induced decomposition γ-AlH3 into constituent elements was found at 15 GPa. Raman scattering study at high pressure for both β- and γ-AlH3 reveals transition into the α phase with high concentration of structural defects. DFT calculations (VASP code) show that instability of cubic β-alane crystal structure at high pressure is caused by the strong deformation of the [AlH6] polyhedra.

Insitu observation of shear stress-induced perovskite to post-perovskite phase transition in CaIrO3 and the development of its deformation texture in a diamond-anvil cell up to 30 GPa

The perovskite (Pv) to post-perovskite (PPv) phase transition and the deformation texture of the PPv phase were investigated on the basis of a high-pressure X-ray diffraction (XRD) study of CaIrO3 using a diamond-anvil cell in a pressure range up to 31GPa. The development of a crystallographic preferred orientation (CPO) in the PPv phase was observed after the plastic deformation from 8 or 9GPa to 31GPa at both room and high (∼1500K) temperatures. The observed CPOs in the present study indicate that the (010) plane worked as an active slip plane in the PPv phase over the entire pressure and temperature range of the present experiment. We also confirmed that the Pv to PPv phase transition proceeds at room temperature under high-stress conditions. The phase transition under high-stress condition is in stark contrast to the results of a previous hydrostatic experiment in which the Pv-CaIrO3 remained stable in a helium media at 31GPa and room temperature. This indicates that shear stress plays an important role in the Pv to PPv phase transition, and this effect should be taken into account when the thermal structure at the D″ layer is discussed on the basis of the high-pressure experiments.

In-situ non-ambient X-ray diffraction studies of indium tungstate

In situ variable temperature and high pressure X-ray diffraction studies were carried out on indium tungstate (In2W3O12). This material displays positive volume expansion in both its low temperature monoclinic and high temperature orthorhombic phases, with negative thermal expansion along the a axis and positive thermal expansion along the b and c axes. Upon hydrostatic compression in a diamond anvil cell, one crystalline to crystalline phase transition is observed in the range 1.9 to 2.7GPa, and progressive irreversible amorphization occurs at pressures above 4.3GPa. The crystalline high pressure phase appears to be isostructural to previously observed high pressure phases in other A2M3O12 compounds.

High-pressure X-ray diffraction study of 1T-TaS2

We present a room temperature high-pressure X-ray diffraction study of the layered compound 1T-TaS2 up to 20GPa. This material is known to exhibit a variety of structural phase transitions that are ascribed to the stabilization of charge density wave states. It has been recently shown that at pressures larger than 3GPa and up to 25GPa, 1T-TaS2 becomes superconductor below about 5K. It was suggested that this superconductivity coexists with different CDW states, an hypothesis that can be tested by X-ray diffraction. Our first results at room temperature show that at around 1.9GPa, the nearly-commensurate (NCCDW) phase transforms into a phase similar to the high temperature incommensurate phase (ICCDW). Above 9GPa, we show the existence of another IC phase, still discernable up to 20GPa despite the pressure-induced crystal damage above 13GPa. These results are consistent with resistivity measurements, but call for a complete exploration of the P–T phase diagram of 1T-TaS2.

High-pressure X-ray diffraction studies of potassium chlorate

Two static high-pressure X-ray diffraction (XRD) studies of potassium chlorate have been performed at pressures of up to ∼14.3 GPa in a diamond anvil cell at ambient temperature using the 16 ID-B undulator beamline at the Advanced Photon Source for the X-ray source. The first experiment was conducted to ascertain decomposition rates of potassium chlorate as a function of pressure. Below 2 GPa, the sample was observed to decompose rapidly in the presence of the X-ray beam and release oxygen. Above 2 GPa (near the phase I → phase II transition), the decomposition rate dramatically slowed so that good quality XRD patterns could be acquired. This suggests a phase-dependent decomposition rate. In the second study, X-ray diffraction spectra were collected at pressures from 2 to 14.3 GPa by aligning virgin portions of the sample into the focused X-ray beam at each pressure. The results suggest the co-existence of mixed monoclinic (I) and rhombohedral (II) phases of potassium chlorate near 2 GPa. At pressures beyond 4 GPa, the XRD patterns show a very good fit to KClO3in the rhombohedral phase with space groupR3m, in agreement with earlier studies. No further phase transitions were observed with pressure. Decompression of the sample to ambient pressure indicated mixed phases I and II coupled with a small amount of synchrotron X-ray-induced decomposition product. The equation of state within this pressure regime has been determined.

High pressure structural stability of BaLiF3

High pressure x-ray diffraction studies on inverse-perovskite BaLiF3 show that this compound is structurally stable up to ∼50 GPa. The bulk modulus of BaLiF3 is determined to be 75.9 GPa which is in close agreement with that determined from a semi-empirical formulation. Our ab initio calculations show that among the three alkaline earth fluoro perovskites (ALiF3, A = Ba, Ca, and Sr) which crystallize in the inverse-perovskite structure, BaLiF3 is the least brittle at ambient conditions and also that the degree of brittleness decreases at high pressures. The behavior of the elastic constants at high pressure accompanied by a reduction in the bandgap indicates a decrease in the directional nature of the bonding.

Compressibility of Fe1.087Te: a high pressure X-ray diffraction study

Fe1.087Te exhibits three phases in the pressure range from ambient to 16.6 GPa and becomes amorphous at higher pressures. All three phases have tetragonal symmetry. The low pressure T-phase is stable in the pressure range 0≤P<4.1 GPa and is found to be relatively soft having zero pressure bulk modulus B 0=36(1) GPa. The intermediate cT-phase is less compressible with B 0=88(5) GPa and stable in the pressure range 4.1≤P<10 GPa while a more compressible phase was observed between 10 and 16.6 GPa.

Magnetic and structural phase transitions in erbium at low temperatures and high pressures

Electrical resistance and crystal structure measurements have been carried out on polycrystalline erbium (Er) at temperatures down to 10 K and pressures up to 20 GPa. An abrupt change in the slope of the resistance is observed with decreasing temperature below 84 K, which is associated with the $c$-axis modulated (CAM) antiferromagnetic (AFM) ordering of the Er moments. With increasing pressure the temperature of the resistance slope change and the corresponding AFM ordering temperature decrease until vanishing above 10.6 GPa. The disappearance of the slope change in the resistance occurs at similar pressures where the hcp structural phase of Er is transformed to a nine-layer \ensuremath{\alpha}-Sm structural phase, as confirmed by our high-pressure synchrotron x-ray diffraction studies. These results suggest that the disappearance in the AFM ordering of Er moments is strongly correlated to the structural phase transition at high pressures and low temperatures.

Brucite [Mg(OH 2)] carbonation in wet supercritical CO 2: An in situ high pressure X-ray diffraction study

Understanding mechanisms and kinetics of mineral carbonation reactions relevant to sequestering carbon dioxide as a supercritical fluid (scCO 2) in geologic formations is crucial to accurately predicting long-term storage risks. Most attention so far has been focused on reactions occurring between silicate minerals and rocks in the aqueous dominated CO 2-bearing fluid. However, water-bearing scCO 2 also comprises a reactive fluid, and in this situation mineral carbonation mechanisms are poorly understood. Using in situ high-pressure X-ray diffraction, the carbonation of brucite [Mg(OH) 2] in wet scCO 2 was examined at pressure (82 bar) as a function of water concentration and temperature (50 and 75 °C). Exposing brucite to anhydrous scCO 2 at either temperature resulted in little or no detectable reaction over three days. However, addition of trace amounts of water resulted in partial carbonation of brucite into nesquehonite [MgCO 3·3H 2O] within a few hours at 50 °C. By increasing water content to well above the saturation level of the scCO 2, complete conversion of brucite into nesquehonite was observed. Tests conducted at 75 °C resulted in the conversion of brucite into magnesite [MgCO 3] instead, apparently through an intermediate nesquehonite step. Raman spectroscopy applied to brucite reacted with 18O-labeled water in scCO 2 show it was incorporated into carbonate at a relatively high concentration. This supports a carbonation mechanism with at least one step involving a direct reaction between the mineral and water molecules without mediation by a condensed aqueous layer.

High pressure investigations of Na0.025WO3: x-ray diffraction and Raman spectroscopy studies

High pressure x-ray diffraction and Raman spectroscopy studies have been carried out on non-stoichiometric sodium tungsten bronze, Na0.025WO3. The high pressure investigations reveal a phase transition at about 2 GPa by a change of space group symmetry from P21/n to P21/c in the monoclinic cell followed by a second structural transformation to a triclinic lattice around 18 GPa. There are volume changes with these structural transformations, which are driven by rotation and significant distortion of WO6 octahedra due to the displacement of tungsten and oxygen atoms from their mean positions in the unit cell.

High pressure phase transitions in the rare earth metal erbium to 151 GPa

High pressure x-ray diffraction studies have been performed on the heavy rare earth metalerbium (Er) in a diamond anvil cell at room temperature to a pressure of 151 GPa and Erhas been compressed to 40% of its initial volume. The rare earth crystal structure sequence fcc (hcp: hexagonal close packed; fcc: face centered cubic; dhcp: double hcp) isobserved in Er below 58 GPa. We have carried out Rietveld refinement of crystalstructures in the pressure range between 58 GPa and 151 GPa. We have examinedvarious crystal structures that have been proposed for the distorted fcc (dfcc)phase and the post-dfcc phase in rare earth metals. We find that the hexagonalhR 24 structure is the best fit between 58 and 118 GPa. Above 118 GPa, a structural transformation fromhR 24 phase to a monoclinicC 2/m phase is observed witha volume change of − 1.9%. We have also established a clear trend for the pressure at which a post-dfcc phase isformed in rare earth metals and show that there is a monotonic increase in this pressurewith the filling of 4f shell.

High Pressure X-Ray Diffraction Study of a Grossular—Andradite Solid Solution and the Bulk Modulus Variation along this Solid Solution

In-situ angle-dispersive x-ray diffraction measurements on three samples of Gr14An84, Gr34An64 and Gr63An34 were performed by using a diamond anvil cell instrument with synchrotron radiation at the Beijing Synchrotron Radiation Facility at up to 13.7 GPa. A least-square fit of the pressure-volume to the Birch—Murnaghan equation of state, when fixed K′0 = 4.0 yields bulk modulus values of K0 = 166±2, 168±3, 173±2 GPa for Gr14An84, Gr34An64 and Gr63An34, respectively. The bulk modulus increases from 166±2 GPa for Gr14An84 and to 173±2 GPa for Gr63An34 with the increasing An content. Furthermore, by linear interpolation, the bulk modulus of the Gr-An binary system as a function of An content can be expressed as K0(GPa) = 176.9(9)-0.12(1)XAn (R2 = 0.987).

Compression of bulk metallic glass Zr57Cu15.4Ni12.6Al10Nb5 to 122 GPa

Ultra high pressure X-ray diffraction studies have been carried out on group IV transition metals-based bulk metallic glass (BMG) Zr57Cu15.4Ni12.6Al10Nb5 to a pressure of 122 GPa at ambient temperature in a diamond anvil cell. Image plate X-ray diffraction studies under high pressure were carried out at a synchrotron source and the two BMG diffraction bands can be followed to the highest pressure using an internal copper pressure standard. Our experiments show that the BMG is stable to compression as high as 40% and thermal activation is needed to nucleate nanostructures/crystallization under extreme conditions. The fit to the Birch–Murnaghan equation of state gives bulk modulus (B 0)=116 GPa and its pressure derivative B′=3.04. The measured differential radial distribution function shows gradual compression of the shell structures in the BMG to extreme compressions.

Low-compressibility of tungsten tetraboride: a high pressure X-ray diffraction study

Diamond anvil cell synchrotron X-ray diffraction (XRD) experiments have been carried out on submicron-sized tungsten tetraboride (WB4) at room temperature up to 50.8 GPa with a silicone oil pressure medium. The crystal structure of WB4 remains unchanged up to the highest pressure. The isothermal bulk modulus K 0 and its pressure derivative, , have been determined from the present compression by fitting the third-order Birch–Murnaghan equation of state: K 0=325±9 GPa and . The high value of the bulk modulus shows that WB4 has high stiffness and/or low-compressibility. Moreover, we also found that the compression behavior of the unit cell axes (a- and c-axes) of WB4 demonstrates an anisotropic nature of compressibility.

High pressure X-ray diffraction study of SrMnO3 perovskite

Using a diamond anvil cell device and synchrotron radiation, the in-situ high-pressure structure of SrMnO3 has been investigated. At pressure up to 28.6 GPa, no pressure-induced phase transition is observed. The lattice parameters as a function of pressure is reported, and the relationship of the axial compression coefficients is βa > βc. The isothermal bulk modulus K298=266(4) GPa is also obtained by fitting the pressure-volume data using the Murnaghan equation of state.

High pressure x-ray diffraction study of the volume collapse in Ba24Si100clathrate

The high pressure stability of the silicon type-III clathrate Ba${}_{24}$Si${}_{100}$ has been studied by x-ray diffraction (XRD) up to a maximum pressure of 37.4 GPa. The high pressure behavior of this Si type-III clathrate appears to be analogous to the structural type-I parent Ba${}_{8}$Si${}_{46}$. An isostructural volume collapse is observed at $~$23 GPa, a value higher than for Ba${}_{8}$Si${}_{46}$ (13--15 GPa). The crystallinity of the structure is preserved up to the maximum attained pressure without amorphization, which appears to be in contradiction with the interpretation given in a Raman spectroscopy study [Shimizu et al., Phys. Rev. B 71, 094108 (2005)]. Nevertheless, the XRD analysis shows the appearance of a type-III disordered nanocaged-based crystalline structure after the volume collapse. Moreover, we find that the volume collapse transformation is (quasi)reversible after pressure release. Additionally, a low pressure transition first evidenced by Raman spectroscopy is also observed in our XRD study at 5 GPa: The variation of the isotropic thermal factors of Ba atoms shows a clear discontinuity at this pressure while the average positions of Ba atoms remain identical.

High pressure X-ray diffraction study of potassium azide

Crystal structure and compressibility of potassium azide was investigated by in-situ synchrotron powder X-ray diffraction in a diamond anvil cell at room temperature up to 37.7 GPa. In the body-centered tetragonal (bct) phase, an anisotropic compressibility was observed with greater compressibility in the direction perpendicular to the plane containing N 3 − ions than directions within that plane. The bulk modulus of the bct phase was determined to be 18.6(7) GPa. A pressure-induced phase transition may occur at 15.5 GPa.

High-pressure synchrotron X-ray diffraction study of the pyrochlores: Ho2Ti2O7, Y2Ti2O7 and Tb2Ti2O7

Synchrotron-based X-ray diffraction was used to study the phase diagrams and determine the compressibilities of the pyrochlore rare-earth titanates Ho2Ti2O7, Y2Ti2O7 and Tb2Ti2O7 to ∼50 GPa. The bulk moduli of the cubic phase of these materials were calculated to be 213±2, 204±3 and 199±1 GPa, respectively. The onset of a structural phase change from cubic to monoclinic was observed near 37, 42 and 39 GPa, respectively. The bulk modulus for the high pressure monoclinic phase of Y2Ti2O7 has been determined to be 185±3 GPa.

High-pressure x-ray diffraction study of CdMoO4 and EuMoO4

We studied the effects of high pressure on the crystalline structure of scheelite-type CdMoO4 and EuMoO4. We found that the compressibility of the materials is highly nonisotropic, with the c-axis being the most compressible one. We also observed clear evidence of a structural phase transition at 12 GPa (CdMoO4) and 8.8 GPa (EuMoO4). The high-pressure phase has a monoclinic structure similar to M-fergusonite. The transition is reversible, and no volume change is detected between the low- and high-pressure phases. The results contradict early x-ray diffraction studies carried out in CdMoO4 and are compared with those obtained previously in isomorphic molybdates. Finally, the equation of state for both compounds is also determined.