Thermal equation of state of CaGeO3 perovskite

Abstract

Pressure-volume-temperature data have been obtained for CaGeO3 perovskite up to 9.6 GPa and 1100 K using a cubic anvil, DIA-type high-pressure apparatus in conjunction with synchrotron X-ray diffraction. The data were analyzed using Birch-Murnaghan equation of state and thermal pressure approach with the bulk modulus at ambient pressure, KT0, and its pressure derivative, K′T0, constrained by previous measurements. A fit of the unit-cell volume data to the high-temperature Birch-Murnaghan (HTBM) equation of state gives (∂KT/∂T)P = -0.025 ± 0.015 GPa/K, a = 1.047 ± 0.356 × 10-5/K, and b = 3.282 ± 0.735 × 10-8/K2 for the thermal expansion α expressed by a + bT. The thermal pressure approach yields αKT = 4.04 ± 0.37 × 10-3 GPa/K and (∂2P/∂T2)V = 6.17 ± 1.28 × 10-6 GPa/K2. The energy dispersive X-ray diffraction data reveal no indication of a structural phase transition over the P-T range of the current experiment. A systematic relationship, KS0 = 6720/V(molar) - 13.07 GPa, has been established based on these isostructural analogues, which predicts KS0 = 261(15) for MgSiO3 perovskite and 225(8) for CaSiO3 perovskite, respectively.