Raman spectroscopy of CaIro3 postperovskite up to 30 GPa

We have measured Raman spectra of the postperovskite (PPv) phase in CaIrO3 up to 30 GPa to constrain the Gruneisen parameter (gamma). 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 Gruneisen parameter, gamma(sp,0) = 1.66 similar to 1.72, constrained from our Raman data, is in excellent agreement with the thermodynamic Gruneisen parameter, gamma(th,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 gamma(sp) constrained by Raman measurements provides a reasonable estimate on the gamma(th) of the PPv phase in CaIrO3.