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The structural stability of gibbsite γ-Al(OH)3 was investigated under high pressure and shear stress conditions by using a rotating diamond anvil cell (RDAC) combining with micro-laser Raman spectroscopy and micro-beam X-ray diffraction. As increasing pressure to 1.5 GPa and rotating to 180°, gibbsite triggers a new structural change at room temperature. In the range of high-wavenumbers, the four peaks of hydroxyl vibration (3 363, 3 434, 3 524 and 3 618 cm-1) disappear gradually, and two new peaks with different intensities appear at 3 303 and 3 560 cm-1. In the range of low-wavenumbers, the intensities of Raman spectra are getting weaker and weaker, but the broad peaks of amorphism are not observed. Both of the double peaks (568, 539 cm-1) of Al-O-Al deformation vibration and the shoulder peaks (321 and 307 cm-1) of Al-O stretching vibration merge into one peak, respectively. However, the four vibration peaks of hydroxyl deformation vibration (1 052, 1 018, 981 and 922 cm-1) still remain. In addition, further increasing pressure to 3.5 GPa and rotating to 360°, and finally decreasing to ambient pressure, two new peaks of hydroxyl stretching vibration in high-wavenumbers, and the peaks of Al-O-Al deformation vibration and Al-O stretching vibration in low-wavenumbers are still observed. Compared to the phase transition of -Al(OH)3 under quasi-hydrostatic pressure conditions, the Raman spectra and phase transition pressure in this study reveal that the -Al(OH)3 take place another new structure change under high pressure and shear stress conditions. The micro-beam X-ray diffraction spectrum of the quenched product reveals that the framework of (OH)-Al-(OH) octahedra of this new phase is still remain, but has a shorter distance between the layers of (OH)-Al-(OH) and a higher symmetry. This newfound structure change of gibbsite in this study mainly due to the inhomogeneous pressure distribution in the sample chamber (from 0.5 to 4.5 GPa). The investigation on structural stability of -Al(OH)3 under high pressure and shear stress conditions is vital for us to identify the stability of hydrous minerals in the cold subduction slabs, and to derive the physical and chemical properties of slab and its subduction rates. [ABSTRACT FROM AUTHOR]

Rhenium tablet is a frequently used gasket material at the ultra-high pressures in Diamond anvil cell (DAC) experiment. Water in deep Earth is the link between material exchange and energy circulation in the Earth's interior. It is greatly scientific and technical significance on the study of chemical reaction of Re- H2O system at high pressures and temperatures. Microscopic observations and Raman measurements show that the Re-H2O system takes place the redox reaction ... under the conditions of high pressures and high temperatures, and produce rhenium oxide (β-ReO2) with Re4+ and atomic hydrogen (H). Observed fourteen characteristic Raman peaks of oxidation product ReO2 have a continuous unequal shift to lower Raman frequencies with the release of pressure. Reduction product H does not further take place interreaction with the water molecules, rhenium metals and their reaction products β-ReO2 and atomic H under high pressures. But the hydrogen molecules are formed when the pressure is released to near atmospheric pressure. The chemical reaction of Re-H2O system under the conditions of high-pressure and temperature reveals that water (hydroxyl) can decompose to produce atomic hydrogen in the Earth's interior with the high pressure, high temperature and reductive material. This discovery not only provides a new experimental evidence for the conversion of water to hydrogen in deep Earth, but also gives important basis for exploring the possible geochemical behaviors of water in the Earth's interior. [ABSTRACT FROM AUTHOR]

Pyrite structure CuS2 was synthesized in diamond anvil cell at high pressures and high temperatures. Using Raman spectroscopy and synchrotron X-ray diffraction, the pyrite-type CuS2 was found to be stable in 0-30 GPa without any phase transition. Raman spectroscopy show that all observed Raman frequencies increasemonotonously with increasing pressures. Fitting experimental pressure and volume data of X-ray diffraction with Birch-Murnaghan equation of state, gives V0 = 193.8(5) ų, K0 = 99(2) GPa and K0' = 4 (fix). The dependencies of Raman frequencies and unit-cell volumes with pressures are coincident with the results of first-principles calculation. The results of calculation properly depict that of experiments. Compared with other pyrite structure transition-metal disulfides MS2(M = Mn, Fe, Co, Ni), the length of M--S dominates the unit-cell volume and compressibility of MS2, and the Cu cation tends to be +2 valance in the CuS2. This study makes up for the lack of high-pressure Raman and XRD research of CuS2, and confirms structural stability of pyrite-type CuS2 at high pressures and high temperatures. The results are important for comprehending the physical and chemical properties of CuS2 and realizing the unified law of pyrite structure materials. It's also meaningful in discussion of the valance and distribution of copper in deep Earth. [ABSTRACT FROM AUTHOR]