High-pressure Raman studies and heat capacity measurements on the MgSiO3 analogue CaIr0.5Pt0.5O3

Hirai S, Kojima Y, Ohfuji H, Nishiyama N, Irifune T, Klemme S, Bromiley G, Attfield JP

Research article (journal)

Abstract

Raman spectroscopy and heat capacity measurements have been used to study the post-perovskite phase of CaIr0.5Pt0.5O3, recovered from synthesis at a pressure of 15 GPa. Laser heating CaIr0.5Pt0.5O3 to 1,900 K at 60 GPa produces a new perovskite phase which is not recoverable and reverts to the post-perovskite polymorph between 20 and 9 GPa on decompression. This implies that Pt-rich CaIr1−xPtxO3 perovskites including the end member CaPtO3 cannot easily be recovered to ambient pressure from high P–T synthesis. We estimate an increase in the thermodynamic Grüneisen parameter across the post-perovskite to perovskite transition of 34%, of similar magnitude to those for (Mg,Fe)SiO3 and MgGeO3, suggesting that CaIr0.5Pt0.5O3 is a promising analogue for experimental studies of the competition in energetics between perovskite and post-perovskite phases of magnesium silicates in Earth’s lowermost mantle. Low-temperature heat capacity measurements show that CaIrO3 has a significant Sommerfeld coefficient of 11.7 mJ/mol K2 and an entropy change of only 1.1% of Rln2 at the 108 K Curie transition, consistent with the near-itinerant electron magnetism. Heat capacity results for post-perovskite CaIr0.5Rh0.5O3 are also reported.

Details zur Publikation

Release year: 2011
Language in which the publication is written: English