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^prime ) = 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 ( (partial K_T /partial T)_P ) = −0.038 ± 0.011 GPa K−1, ( alpha K_T ) = 0.0039 ± 0.0001 GPa K−1, ( left( {partial K_T /partial T} ight)_V ) = −0.012 ± 0.002 GPa K−1, and ( left( {partial² P/partial T² } ight)_V ) = 1.9 ± 0.3 × 10−6 GPa2 K−2. Using the Mie-Grüneisen-Debye formalism, we obtain Grüneisen parameter ( gamma₀ ) = 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.