Journal
PHYSICS AND CHEMISTRY OF MINERALS
Volume 38, Issue 8, Pages 631-637Publisher
SPRINGER
DOI: 10.1007/s00269-011-0435-2
Keywords
Post-perovskite; Perovskite; High pressure; Raman spectroscopy
Categories
Funding
- EPSRC
- Leverhulme Trust, UK
- Grants-in-Aid for Scientific Research [21740382, 20244086] Funding Source: KAKEN
- Engineering and Physical Sciences Research Council [EP/G030332/1] Funding Source: researchfish
- EPSRC [EP/G030332/1] Funding Source: UKRI
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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 Gruneisen 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 K-2 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.
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