Calorimetric study of perovskite solid solutions in the CaSio3-CaGeO3 system

H. Kojitani, A. Navrotsky, M. Akaogi

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

Enthalpies of drop solution (ΔHdrop-sol) of CaGeO3, Ca(Si0.1Ge0.9)O3, Ca(Si0.2Ge0.8)O3, Ca(Si0.3-Ge0.7)O3 perovskite solid solutions and CaSiO3 wollastonite were measured by high-temperature calorimetry using molten 2PbO · B2O3 solvent at 974 K. The obtained values were extrapolated linearly to the CaSiO3 end member to give ΔHdrop-sol of CaSiO3 perovskite of 0.2 ± 4.4 kJ mol-1. The difference in ΔHdrop-sol between CaSiO3, wollastonite, and perovskite gives a transformation enthalpy (wo → pv) of 104.4 ± 4.4 kJ mol-1. The formation enthalpy of CaSiO3 perovskite was determined as 14.8 ± 4.4 kJ mol-1 from lime + quartz or -22.2 ± 4.5 kJ mol-1 from lime + stishovite. A comparison of lattice energies among A2+B4+O3 perovskites suggests that amorphization during decompression may be due to the destabilizing effect on CaSiO3 perovskite from a large nonelectrostatic energy (repulsion energy) at atmospheric pressure. By using the formation enthalpy for CaSiO3 perovskite, phase boundaries between β-Ca2SiO4 + CaSi2O5 and CaSiO3 perovskite were calculated thermodynamically utilizing two different reference points [where ΔG(P,T) = 0] as the measured phase boundary. The calculations suggest that the phase equilibrium boundary occurs between 11.5 and 12.5 GPa around 1500 K. Its slope is still not well constrained.

Original languageEnglish (US)
Pages (from-to)413-420
Number of pages8
JournalPhysics and Chemistry of Minerals
Volume28
Issue number6
DOIs
StatePublished - 2001
Externally publishedYes

Keywords

  • CaGeO
  • Calorimetry
  • CaSiO
  • High pressure phase transition
  • Perovskite

ASJC Scopus subject areas

  • Materials Science(all)
  • Geochemistry and Petrology

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