ining Ma

High Pressure Elastic Behavior of Synthetic Mg3Y2( SiO4)(3) Garnet up to 9 GPa

The compression behavior of synthetic magnesium- (Mg-) yttrium (Y) garnet Mg3Y2(SiO4)3 has been investigated upto about 8.79 GPa at 300 K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at the beamline X17C, National Synchrotron Light Source, Brookhaven National Laboratory. No phase transition has been observed within the pressure range investigated. The unit-cell parameters and volume decreased systematically with increasing pressure, and a reliable isothermal bulk modulus () and its pressure derivative () were obtained in this study. The values of zero-pressure volume , , and refined with a third-order Birch-Murnaghan equation of state are  Å3,  GPa, and . If is fixed at 4, is obtained as  GPa.

A simple external resistance heating diamond anvil cell and its application for synchrotron radiation x-ray diffraction

A simple external heating assemblage allowing diamond anvil cell experiments at pressures up to 34 GPa and temperatures up to 653 K was constructed. This cell can be connected to the synchrotron radiation conveniently. The design and construction of this cell are fully described, as well as its applications for x-ray diffraction. Heating is carried out by using an external-heating system, which is made of NiCr resistance wire, and the temperature was measured by a NiCr-NiSi or PtRh-Pt thermocouple. We showed the performance of the new system by introducing the phase transition study of cinnabar (alpha-HgS) and thermal equation of state study of almandine at high pressure and temperature with this cell.

Compression and structure of brucite to 31 GPa from synchrotron X-ray diffraction and infrared spectroscopy studies

Abstract Synchrotron X-ray powder diffraction and infrared (IR) spectroscopy studies on natural brucite were conducted up to 31 GPa using diamond-anvil cell (DAC) techniques at beamlines X17C and U2A of National Synchrotron Light Source (NSLS). The lattice parameters and unit-cell volumes were refined in P3̄m1 space group throughout the experimental pressure range. The anisotropy of lattice compression decreases with pressure due to a more compressible c axis and the compression becomes nearly isotropic in the pressure range of 10-25 GPa. The unit-cell volumes are fitted to the third-order Birch-Murnaghan equation of state, yielding K0 = 39.4(1.3) GPa, K0′ = 8.4(0.4) for the bulk modulus and its pressure-derivative, respectively. No phase transition or amorphization was resolved from the X-ray diffraction data up to 29 GPa, however, starting from ~4 GPa, a new infrared vibration band (~3638 cm-1) 60 cm-1 below the OH stretching A2u band of brucite was found to coexist with the A2u band and its intensity continuously increases with pressure. The new OH stretching band has a more pronounced redshift as a function of pressure (-4.7 cm-1/GPa) than the A2u band (-0.7 cm-1/ GPa). Comparison with first-principles calculations suggests that a structural change involving the disordered H sublattice is capable of reconciling the observations from X-ray diffraction and infrared spectroscopy studies.

Compressibility of mimetite and pyromorphite at high pressure

High pressure X-ray diffraction experiments on mimetite [Pb5(AsO4)3Cl] and pyromorphite [Pb5(PO4)3Cl] were performed up to 14.1 and 14.9 GPa, respectively, at 300 K, using in situ angle-dispersive X-ray diffraction and a diamond anvil cell. No phase transition of mimetite and pyromorphite was observed within the experimental pressure range. Fitting the P–V data under hydrostatic stress conditions with a third-order Birch–Murnaghan Equations of State (BM-EoS) we obtained: K 0=46(7) GPa, V 0=680(2) Å3, and K 0′=15(4) for mimetite; K 0=44(5) GPa, V 0=636(1) Å3, and K 0′=15(3) for pyromorphite. The axial compressibility was also calculated with a third-order ‘linearized’ BM-EoS. We obtained K 0a :K 0c =1:1.00 for mimetite, and K 0a :K 0c =1:1.28 for pyromorphite, indicating that mimetite and pyromorphite are elastically isotropic and slightly anisotropic, respectively. Comparing the previous equation of state data of vanadinite [Pb5(VO4)3Cl] with the current results of mimetite [Pb5(AsO4)3Cl] and pyromorphite [Pb5(PO4)3Cl], we found that the substitution of V5+ by As5+ and P5+ has an insignificant effect on the bulk modulus, but has a greater effect on the axial parameters, compression ratio, and elastic anisotropy.

In Situ High-Pressure Synchrotron X-Ray Diffraction Study of Clinozoisite

We investigate the elastic behavior of a natural clinozoisite under about 20.4 GPa at 300 K using in situ angle-dispersive x-ray diffraction and a diamond anvil cell at the National Synchrotron Light Source, Brookhaven National Laboratory. Over this pressure range, no phase change or disproportionation has been observed. The isothermal equation of state is determined. The values of V0 and K0 refined by the Murnaghan equation of state are V0 = 460.0 ± 0.2 A3, K0 = 138 ± 3 GPa. Consequently, it can be concluded that the compressibility of clinozoisite under high pressures is accurately constrained.

P-V-T equation of state of Ca3Cr2Si3O12 uvarovite garnet by using a diamond-anvil cell and in-situ synchrotron X-ray diffraction

Abstract The pressure-volume-temperature (P-V-T) equation of state (EoS) of synthetic uvarovite has been measured at high temperatures up to 900 K and high pressures up to 16.20 GPa, by using in situ angle-dispersive X-ray diffraction and diamond-anvil cell. Analysis of room-temperature P-V data to a third-order Birch-Murnaghan EoS yielded: V0 = 1736.9 ± 0.5 Å3, K0 = 162 ± 2 GPa, and K′0 = 4.5 ± 0.3. With K′0 fixed to 4.0, we obtained: V0 = 1736.5 ± 0.3 Å3 and K0 = 164 ± 1 GPa. Fitting of our PV- T data by means of the high-temperature third-order Birch-Murnaghan equations of state, given the thermoelastic parameters: V0 = 1736.8 ± 0.8 Å3, K0 = 162 ± 3 GPa, K′0 = 4.3 ± 0.4, (∂K/∂T)P = -0.021 ± 0.004 GPa/K, and α0 = (2.72 ± 0.14)×10-5 K-1. We compared our elastic parameters to the results from the previous studies for uvarovite. From the comparison of these fittings, we propose to constrain the bulk modulus and its pressure derivative to K0 = 162 GPa and K′0 = 4.0-4.5 for uvarovite. Present results were also compared with previous studies for other ugrandite garnets, grossular and andradite, which indicated that the compression mechanism of uvarovite might be similar with grossular and andradite. Furthermore, a systematic relationship, K0 (GPa) = 398.1(7)-0.136(8) V0 (Å3) with a correlation coefficient R2 of 0.9999, has been established based on these isostructural analogs. Combining these results with previous studies for pyralspite garnets-pyrope, almandine, and spessartine-the compositional dependence of the thermoelastic parameters (bulk modulus, thermal expansion, and the temperature derivative of the bulk modulus) were discussed.

Elasticity and phase transformation at high pressure in coesite from experiments and first-principles calculations

Abstract The crystal structure and equation of state of coesite (space group C2/c) and its high-pressure polymorph coesite-II (space group P21/n) under pressure have been studied using X-ray powder diffraction in a diamond-anvil cell (DAC) up to 31 GPa at room-temperature and first-principles calculations at 0 K up to 45 GPa. New diffraction peaks appear above 20 GPa, indicating the formation of coesite-II structure. The calculated enthalpies provide theoretical support for the pressure-induced phase transformation from coesite to coesite-II at ~21.4 GPa. Compared with coesite, the coesite-II structure is characterized by a “doubled” b-axis and the breakdown of the linear Si1-O1-Si1 angle in coesite into two distinct angles—one is ~176°, close to linear, whereas the other decreases by 22 to 158°. Coesite is very anisotropic with the a-axis the shortest and twice more compressible than the b- and c-axis. By comparison, coesite-II is not so anisotropic with similar compressibilities in its a-, b-, and c-axis. As analyzed by a third-order Eulerian finite strain equation of state, the bulk modulus of coesite at 21.4 GPa is 182.3 GPa, and that of coesite-II is 140.8 GPa, indicating that coesite-II is much more compressible than coesite. The existence of coesite-II in the coldest subduction zone will change the elasticity and anisotropic properties of the subducting materials dramatically.

The elasticity of natural hypersthene and the effect of Fe and Al substitution

ABSTRACT Compressional behavior of a natural hypersthene has been investigated at pressures up to 10.1 GPa at room temperature using in situ synchrotron X-ray diffraction in a diamond anvil cell. No phase transition was observed within the experimental pressure range. The pressure–volume data have been fitted with a third-order Birch–Murnaghan equation of state, resulting in K0 = 113.6(6.2) GPa and for the bulk modulus and its pressure derivative with a fixed unit-cell volume V0 = 854.0(6) Å3. The unit-cell parameters, a, b, and c, decrease nonlinearly with elevated pressure and show an anisotropic axial compressibility with a ratio βa: βb: βc: =1:2.05:1.3. The comparison with previous results of orthopyroxene reveals that Al substitution causes a decrease in unit-cell volume and an increase in the bulk modulus, whereas the incorporation of Fe has opposite effects. The relation between unit-cell volume and En/Ts contents has been obtained, V0 (Å3) = 873.7(1.1) − 40.8(1.44)  ×  En-90.6(14.7)  ×  Ts, which permits the prediction of unit-cell volume for Fe- and Al-bearing orthopyroxene system.