We have measured Raman spectra of the postperovskite (PPv) phase in CaIrO3 up to 30 GPa to constrain the Grüneisen parameter (γ). We identified a total of 4 strong modes between 200 and 650 cm−1, which is in contrast with the Raman spectra of Mn2O3 and MgGeO3-PPv where at least nine different modes have been detected. We found no sign of a phase transition in the Raman spectra of PPv CaIrO3, which supports the stability of the PPv phase up to 30 GPa and room temperature in CaIrO3. The spectroscopic Grüneisen parameter, γsp,0 = 1.66~1.72, constrained from our Raman data, is in excellent agreement with the thermodynamic Grüneisen parameter, γth,0 = 1.75 ± 0.05, calculated from recent XRD measurements (Martin et al. 2007) on CaIrO3-PPv synthesized at high pressure and temperature similar to our starting material. Our result suggests that γsp constrained by Raman measurements provides a reasonable estimate on the γth of the PPv phase in CaIrO3.

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