Raman spectroscopy of CaIrO3 postperovskite up to 30 GPa

Abstract

We have measured Raman spectra of the postperovskite (PPv) phase in CaIrO{sub 3} up to 30 GPa to constrain the Grueneisen parameter ({gamma}). We identified a total of 4 strong modes between 200 and 650 cm{sup -1}, which is in contrast with the Raman spectra of Mn{sub 2}O{sub 3} and MgGeO{sub 3}-PPv where at least nine different modes have been detected. We found no sign of a phase transition in the Raman spectra of PPv CaIrO{sub 3}, which supports the stability of the PPv phase up to 30 GPa and room temperature in CaIrO{sub 3}. the spectroscopic Grueneisen parameter, {gamma}{sub sp,0} = 1.66--1.72, constrained from our Raman data, is in excellent agreement with the thermodynamic Grueneisen parameter, {gamma}{sub th,0} = 1.75 {+-} 0.05, calculated from recent XRD measurements (Martin et al. 2007) on CaIrO{sub 3}-PPv synthesized at high pressure and temperature similar to our starting material. Our result suggests that {gamma}{sub sp} constrained by Raman measurements provides a reasonable estimate on the {gamma}{sub th} of the PPv phase in CaIrO{sub 3}.