Thermal equation of state of CaIrO₃ post-perovskite

The pressure-volume-temperature (P-V-T) relation of CaIrO₃ post-perovskite (ppv) was measured at pressures and temperatures up to 8.6 GPa and 1,273 K, respectively, with energy-dispersive synchrotron X-ray diffraction using a DIA-type, cubic-anvil apparatus (SAM85). Unit-cell dimensions were derived from the Le Bail full profile refinement technique, and the results were fitted using the third-order Birth-Murnaghan equation of state. The derived bulk modulus K_T0 at ambient pressure and temperature is 168.3 ± 7.1 GPa with a pressure derivative K′_T0 = 5.4 ± 0.7. All of the high temperature data, combined with previous experimental data, are fitted using the high-temperature Birch-Murnaghan equation of state, the thermal pressure approach, and the Mie-Grüneisen-Debye formalism. The refined thermoelastic parameters for CaIrO₃ ppv are: temperature derivative of bulk modulus (∂K_T/∂T)_P = -0.038 ± 0.011 GPa K^-1, αK_T = 0.0039 ± 0.0001 GPa K^-1,(∂K_T/∂T)_V = -0.012 ± 0.002 GPa K^-1, and (∂²P/∂T²)_V = 1.9 ± 0.3 × 10^-6 GPa² K^-2. Using the Mie-Grüneisen-Debye formalism, we obtain Grüneisen parameter γ₀ = 0.92 ± 0.01 and its volume dependence q = 3.4 ± 0.6. The systematic variation of bulk moduli for several oxide post-perovskites can be described approximately by the relationship K_T0 = 5406.0/V(molar) + 5.9 GPa.