High-pressure X-ray Diffraction Study Research Articles

Strength of polycrystalline coarse-grained platinum to 330GPa and of nanocrystalline platinum to 70GPa from high-pressure x-ray diffraction data

X-ray diffraction patterns from platinum foil (∼300nm grain size) have been recorded up to 330GPa using a beveled-anvil diamond cell. The compressive strength has been determined from the analysis of the diffraction linewidths. In a separate set of experiments, coarse-grained platinum powder (∼300nm grain size) is compressed up to 64GPa in a diamond anvil cell with 300μm flat-face anvils and diffraction patterns are recorded. The strengths as functions of pressure derived in the two sets of experiments agree well. The strength increases linearly from 0.21(2)GPa at zero pressure to 9.8(4)GPa at a pressure of 330GPa. The nanocrystalline platinum sample (∼20nm average grain size) exhibits much higher strength and increases linearly from 3.0(1)to8.0(3)GPa as the pressure is increased from zero pressure to 70GPa. The grain size of nanocrystalline sample decreases with increasing pressure. The effect of nonhydrostatic compression on the pressures determined with platinum as a pressure marker in high-pressure x-ray diffraction studies is discussed.

In situ high-pressure x-ray diffraction study of H2O ice VII

Ice VII was examined over the entire range of its pressure stability by a suite of x-ray diffraction techniques in order to understand a number of unexplained characteristics of its high-pressure behavior. Axial and radial polycrystalline (diamond anvil cell) x-ray diffraction measurements reveal a splitting of diffraction lines accompanied by changes in sample texture and elastic anisotropy. In situ laser heating of polycrystalline samples resulted in the sharpening of diffraction peaks due to release of nonhydrostatic stresses but did not remove the splitting. Radial diffraction measurements indicate changes in strength of the material at this pressure. Taken together, these observations provide evidence for a transition in ice VII near 14 GPa involving changes in the character of the proton order/disorder. The results are consistent with previous reports of changes in phase boundaries and equation of state at this pressure. The transition can be interpreted as ferroelastic with the appearance of spontaneous strain that vanishes at the hydrogen bond symmetrization transition near 60 GPa.

Compressibility trends of the clinopyroxenes, and in-situ high-pressure single-crystal X-ray diffraction study of jadeite

The crystal structure of a natural jadeite, NaAlSi2O6, was studied at room temperature over the pressure range 0–9.17 GPa using single-crystal X-ray diffraction. Unit-cell data were determined at 16 pressures, and intensity data were collected at nine of these pressures. A third-order Birch-Murnaghan equation of state fit to the P-V data yielded V = 402.03(2) A3, K = 136.5(14) GPa, and K ′ = 3.4(4) Jadeite exhibits strongly anisotropic compression with unit strain axial ratios of 1.00:1.63:2.10. Silicate chains become more O-rotated with pressure, reducing ∠O3-O3-O3 from 174.7(1)° at ambient pressure to 169.2(6)° at 9.17 GPa and bringing the anions of jadeite closer to a cubic closest-packed arrangement. No evidence of a phase transition was observed over the studied pressure range. In an effort to understand pyroxene compressibilities, selected clinopyroxene bulk moduli were plotted against ambient unit-cell volumes. Two trends were identified and are explained in terms of differences in M2-O3 bonding topologies and the geometric relationship of the bonds with tetrahedral rotation in the silicate chains. Bonds positioned to favor the tetrahedral rotation upon compression are termed “sympathetic,” whereas bonds positioned to resist the rotation are termed “antipathetic.” Examination of the different pyroxene structures indicates that structures containing antipathetic M2-O3 bonds are less compressible than those with only sympathetic M2-O3 bonds. This behavior has not been previously recognized.

高圧下における含水 Ｍｇ 珪酸塩融体の構造変化とその水の役割

In situ high-pressure X-ray diffraction studies on the structure of hydrous Mg-silicate melts have been performed at superliquidus temperatures up to 7 GPa using a newly developed encapsulation method. The results of in situ experiments on hydrous silicate melts demonstrate the characteristic structural changes in the silicate network and local structures with pressure. This paper discusses the effect of water on the silicate network and the short-range order of a hydrous silicate melt at high pressures, based on the recent structural studies and previous works on silicate glasses.

High-pressure X-ray diffraction study of SrMoO 4 and pressure-induced structural changes

SrMoO 4 was studied under compression up to 25 GPa by angle-dispersive X-ray diffraction. A phase transition was observed from the scheelite-structured ambient phase (space group I4 1/ a) to a monoclinic fergusonite phase (space group I2 /a) at 12.2(9) GPa. The unit-cell parameters of the high-pressure phase are a=5.265(9) Å, b=11.191(9) Å, c=5.195 (5) Å, and β=90.9(1)°, Z=4 at 13.1 GPa. There is no significant volume collapse at the phase transition. No additional phase transitions were observed and on release of pressure the initial phase is recovered, implying that the observed structural modifications are reversible. The reported transition appeared to be a ferroelastic second-order transformation producing a structure that is a monoclinic distortion of the low-pressure phase and was previously observed in compounds isostructural to SrMoO 4. A possible mechanism for the transition is proposed and its character is discussed in terms of the present data and the Landau theory. Finally, the room temperature equation of states is reported and the anisotropic compressibility of the studied crystal is discussed in terms of the compression of the Sr–O and Mo–O bonds.

High-pressure optical spectroscopy and X-ray diffraction studies on synthetic cobalt aluminum silicate garnet

The pressure-induced behavior of spin-allowed dd-bands of VIII Co 2+ in the absorption spectra of synthetic Co 3 Al 2 Si 3 O 12 garnet was studied from 10 -4 to 13 GPa. The plots of the peak energy vs. pressure for the three sharpest well resolved bands at ca. 5160, 17 680, and 18 740 cm -1 display small but discernible breaks in linear relations between 4 and 5 GPa. Data from single-crystal X-ray diffraction likewise show discontinuities in trends of CoO 8 polyhedral volume and distortion, and Co-O and Si-O bond distances over this pressure range. These effects are related to a pressure-induced phase transition from the β- to α-isostructural polymorph of Co 3 Al 2 Si 3 O 12 .

Pressure-induced crystallization and phase transformation of amorphous selenium: Ramanspectroscopy and x-ray diffraction studies

High-pressure Raman spectroscopy studies have been carried out on amorphous Se (a-Se)at room temperature in a diamond anvil cell with an 830 nm exciting line. Raman evidencefor the pressure-induced crystallization of a-Se and the coexistence of the unknownhigh-pressure phase with the hexagonal phase is presented for the first time. Furtherexperimental proof of high-pressure angle-dispersive x-ray diffraction studies for a-Seindicates that the unknown high-pressure phase is also a mixture phase of the tetragonalI41/acd and Se IV structure. Our Raman and x-ray diffraction results suggest that hexagonal Se Iundergoes a direct transition to triclinic Se III at about 19 GPa, which is in good agreementwith the theoretical prediction.

In situ study of icosahedral Zn–Mg–Dy and Co-rich decagonal Al–Co–Ni at high pressuresand high temperatures

An in situ high-pressure high-temperature x-ray diffraction study on single-crystallineicosahedral Zn–Mg–Dy up to 12.5(4) GPa at 873 K and powdered Co-rich decagonalAl–Co–Ni up to 12.3(4) GPa at 973 K has been performed using a heatable diamond-anvilcell and synchrotron radiation. Quantitative reciprocal-space reconstruction from imageplate data was used for evaluating the single-crystal data. The compressibility of thematerials at ambient temperature was determined from x-ray powder diffraction up to30.3(2) GPa for icosahedral Zn–Mg–Dy and 61.4(1) GPa for Co-rich decagonalAl–Co–Ni. The bulk modulus at zero pressure and its pressure derivative weredetermined from fitting third-order Birch–Murnaghan equations of state asK0 = 92(4) GPa,K′ = 3.1(3) for icosahedralZn–Mg–Dy and K0 = 120(11) GPa, K′ = 7.1(7) for Co-rich decagonal Al–Co–Ni, respectively. The compressibilities of the quasicrystals arediscussed with respect to their structure types and the available literature data. To afirst approximation, a linear dependency of the squared electron density at theborder of the Wigner–Seitz atomic cell from the ratio of the bulk modulus and themolar volume was found. This behaviour is comparable to that of periodic alloys.

Pressure induced phase transformation of REH 3

High-pressure X-ray diffraction studies of the number of rare earth trihydrides (REH 3) have been carried out in a diamond anvil cell up to 30 GPa at room temperature. This includes the family of rare earth trihydrides that possess hexagonal structure at ambient conditions. A reversible structural phase transformation from the hexagonal to cubic phase has been observed for the Sm, Gd, Er, Ho and luthetium trihydrides. The same type of phase transition has been found also for yttrium trihydride. The lattice parameters of the new cubic phases and the volume changes at transition points were determined for the all compounds investigated. The parameters of the equation of state for all the hexagonal and cubic phases have been determined in the pressure range up to 30 GPa. The role of H–H repulsive interaction as a probable promoter of the transition and a systematics of transition are discussed.

Compressibility of zinc sulfide nanoparticles

We describe a high-pressure x-ray diffraction (XRD) study of the compressibility of several samples of ZnS nanoparticles. The nanoparticles were synthesized with a range of sizes and surface chemical treatments in order to identify the factors that determine nanoparticle compressibility. Refinement of the XRD data revealed that all ZnS nanoparticles in the nominally cubic (sphalerite) phase exhibited a previously unobserved structural distortion under ambient conditions that exhibited, in addition, a dependence on pressure. Our results show that the compressibility of ZnS nanoparticles increases substantially as the particle size decreases, and we propose an interpretation based upon the available mechanisms of structural compliance in nanoscale vs bulk materials.

High pressure X-ray diffraction study of tungsten disulfide

Abstract Synchrotron X-ray diffraction was used in conjunction with a diamond anvil cell to investigate the properties of a tungsten diselenide (WSe2) sample to 35.8 GPa at room temperature. By fitting the pressure–volume data to the third-order Birch–Murnaghan equation of state, the bulk modulus, K0T, of WSe2 was determined to be 72±1 GPa with its pressure derivative, K 0 T ′ , being 4.1±0.1. It was also found that the c-direction of the hexagonal structure is significantly more compressible than the a-direction. No phase transformation was clearly observed in the pressure range of our measurements.

High-pressure x-ray diffraction study of Ta4AlC3

Using a synchrotron radiation source and a diamond anvil cell, we measured the pressure dependence of the lattice parameters of a recently discovered phase, Ta4AlC3. This phase adopts a hexagonal structure with the space group P63∕mmc; at room conditions, the a and c parameters are 3.087(5) and 23.70(4)Å, respectively. Up to a pressure of 47GPa, no phase transformations were observed. Like Ta2AlC, but unlike many related phases such as Ti4AlN3, Ti3SiC2, Ti3GeC2, and Zr2InC, the compressibility of Ta4AlC3 along the c and a axes are almost identical. The bulk modulus of Ta4AlC3, 261±2GPa, is ≈4% greater than that of Ta2AlC. Both, however, are ≈37% lower than the 345±9GPa of TaC.

High-pressure x-ray diffraction study of the giant dielectric constant material CaCu3Ti4O12: Evidence of stiff grain surface

We measured the high-pressure x-ray diffraction of the giant dielectric constant material CaCu3Ti4O12 (CCTO) under both hydrostatic and uniaxial compressions. We found that the cubic structure of CCTO is stable up to 57GPa. Nevertheless we observed that CCTO has unusual compression behaviors under hydrostatic pressure. Specifically, the volume reduction is less than that under uniaxial compression below 25GPa, above it the volume reduction starts to approach and finally reaches the same value as that under the uniaxial compression at about 30GPa. We explained these remarkable phenomena by using the model that the samples are composed of grains that have shells stiffer than the cores.

High pressure X-ray diffraction study of CdAl2Se4 and Raman study of AAl2Se4 (A=Hg, Zn) and CdAl2X4 (X=Se, S)

We report the results of an X-ray diffraction study of CdAl2Se4 and of Raman studies of HgAl2Se4 and ZnAl2Se4 at room temperature, and of CdAl2S4 and CdAl2Se4 at 80 K at high pressure. The ambient pressure phase of CdAl2Se4 is stable up to a pressure of 9.1 GPa above which a phase transition to a disordered rock salt phase is observed. A fit of the volume pressure data to a Birch–Murnaghan type equation of state yields a bulk modulus of 52.1 GPa. The relative volume change at the phase transition at ∼9 GPa is about 10%. The analysis of the Raman data of HgAl2Se4 and ZnAl2Se4 reveals a general trend observed for different defect chalcopyrite materials. The line widths of the Raman peaks change at intermediate pressures between 4 and 6 GPa as an indication of the pressure induced two stage order–disorder transition observed in these materials. In addition, we include results of a low temperature Raman study of CdAl2S4 and CdAl2Se4, which shows a very weak temperature dependence of the Raman-active phonon modes.

High-pressure X-ray diffraction study of PrFe 4P 12

The filled skutterudite PrFe 4P 12 undergoes an antiferro-quadrupolar (AFQ) ordering below T Q = 6.5 K . In a recent resistivity measurement under high pressures, it was reported that T Q is suppressed with applied pressure and an insulating phase appears above 2.4 GPa. To obtain microscopic information about the AFQ phase and the insulating state under pressure, we performed X-ray diffraction experiments. We have succeeded in observing superlattice reflections at the wave vector q = ( 1 , 0 , 0 ) with the intensity being ∼ 10 - 4 of the fundamental Bragg's ones. At 1.4 GPa, T Q is suppressed to 5.5 K, while it is found out that the calculated Fe-ion displacement is almost the same as that at ambient pressure. In the insulating state, on the other hand no superlattice reflections at q = ( 1 , 0 , 0 ) are observed within the experimental error.

High-pressure x-ray and neutron powder diffraction study ofPbWO4 and BaWO4 scheelites

The room-temperature high-pressure behaviour ofPbWO4 andBaWO4 scheelites(I41/a,Z = 4) has been studied with synchrotron angle-dispersive x-ray powder diffractionin a diamond anvil cell and time-of-flight neutron powder diffraction in alarge-volume Paris–Edinburgh cell. Full profile Rietveld refinements of theneutron data provide evidence for distinct compressibility mechanisms in thesematerials. The distortion in the anionic array from the ideal fluorite packing inBaWO4 increases upon compression while it decreases inPbWO4.

High pressure X-ray diffraction study of all Fe–Sn intermetallic compounds and one Fe–Sn solid solution

Abstract The present study describes the preparation of all five Fe–Sn intermetallic compounds, FeSn 2 , FeSn, Fe 3 Sn 2 , Fe 5 Sn 3 , and Fe 3 Sn, and the results of the X-ray diffraction study under static high pressure up to 25 GPa using nitrogen as a pressure-transmitting medium. The samples were prepared with phase purities of 97% and higher. Four Fe–Sn intermetallics, FeSn 2 , FeSn, Fe 5 Sn 3 , and Fe 3 Sn, show no phase transition to the highest pressure achieved; Fe 3 Sn 2 undergoes two transitions to 25 GPa. The bulk moduli of these materials decrease approximately linearly with increasing Sn content, with the exception of Fe 3 Sn 2 . We also studied the solubility of Sn in α-Fe (α-Fe 1− x Sn x ). Tin expands the α-Fe lattice according to Vegard's law to at least 6 at.% Sn. The solid solution α-Fe 0.92 Sn 0.08 was examined beyond the pressure of the α/ɛ-phase transition. The onset of the phase transition in α-Fe 0.92 Sn 0.08 occurs at about 24 GPa, higher than the transition pressure of 14 GPa in pure α-Fe, but at a similar lattice parameter, a ≈ 2.800 A.

High pressure X-ray diffraction studies of purely siliceous zeolites

High pressure X-ray diffraction studies of purely siliceous zeolites

High pressure X-ray diffraction study of MgMn2O4 tetragonal spinel

The phase stability of the MgMn2O4 spinel has been studied by means of high-pressure X-ray diffraction for pressures up to 30GPa. Two samples with different inversion degrees have been considered. Both spinels undergo a phase transition towards an orthorhombic structure (CaMn2O4-type). For the more inverted sample the transition pressure is at least 1GPa lower with respect to that of the less inverted spinel. Also the volume contraction, relative compressibility and density trends are different for the two samples. These variations have been explained according to the differences in cation distribution and electronic properties of the samples.

Structural Refinement of the High-Pressure Phase of Aluminum Trihydroxide: In-Situ High-Pressure Angle Dispersive Synchrotron X-ray Diffraction and Theoretical Studies

In-situ high-pressure synchrotron angle-dispersive X-ray diffraction for gibbsite (aluminum trihydroxide) was performed at room temperature up to 20 GPa. A pressure-induced phase transition was observed at 2.6 GPa. The new high-pressure phase can be recovered at ambient pressure. Rietveld refinement shows that the new phase of Al(OH)(3) has an orthorhombic structure, spacegroup Pbca, and the lattice parameters at ambient condition are a = 868.57(5) pm, b = 505.21(4) pm, c = 949.54(6) pm, V = 416.67(6) x 10(6) pm(3) with Z = 8. The compressibility of gibbsite and the high-pressure polymorph was analyzed, and their bulk moduli were estimated as 49.8 +/- 1.8 and 81.0 +/- 5.2 GPa, respectively. First-principles calculations of the high-pressure phase were performed to determine the hydrogen positions and to confirm the structural stability of the new phase.