In chapter 1, we investigate the elastic properties of diopside, CaMgSi2O6, at ambient pressure and room temperature by Brillouin spectroscopy. The thirteen single-crystal elastic moduli (Cij) of two samples of diopsidic pyroxenes close to the ideal composition from different locations have been measured. No unusual compositional dependence of Cij values or the shear modulus near end-member diopside composition is observed.In chapter 2, we further investigate the elastic properties of diopside at high pressure using a diamond anvil cell. The single-crystal elastic constants of diopside have been measured up to 14 GPa using Brillouin spectroscopy, from which the aggregate compressional and shear velocities, adiabatic bulk modulus, shear modulus and their pressure derivatives were obtained. This study not only provides the first high-pressure experimental data on the individual Cij’s but also extends direct measurements on shear modulus for diopside to higher pressure than previous studies.Chapter 3 describes the thermodynamic properties of H2O. We determined the melting curve of Ice VII by simultaneous measurements of sound velocity and angle-dispersive synchrotron x-ray diffraction in a membrane-type diamond anvil cell with resistance heating at elevated temperatures to 873 K at pressures of 2 GPa to 14 GPa. We observed higher melting curves than previous studies, with the discrepancy increasing to ~120 K at 8 GPa. The sound velocity of liquid H2O was measured up to 723K and 6.3 GPa. Measured sound speeds are significantly lower than previous acoustic measurements, with the discrepancy as high as 9% along 723K isotherm. A tentative equation of state (EOS) for liquid H2O was obtained with the velocity – pressure – temperature data. More sound velocity data at different pressure along several high-temperature isotherms is required for a more accurate estimate of the EOS.
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