Aluminum in magnesium silicate perovskite: Synthesis and energetics of defect solid solutions

Alexandra Navrotsky, Mirko Schoenitz, Hiroshi Kojitani, Hongwu Xu, Jianzhong Zhang, Donald J. Weidner, Masaki Akaogi, Raymond Jeanloz

Research output: Contribution to journalConference articlepeer-review

1 Scopus citations

Abstract

MgSiO3 - rich perovskite is expected to dominate the Earth's lower mantle (pressures > 25 GPa), with iron and aluminum as significant substituents. The incorporation of trivalent ions, M3+, may occur by two competing mechanisms MgA + SiB = MA + MB and SiB = AlB + 0.5 VO. Phase synthesis studies show that both substitutions do occur, and the nonstoichiometric or defect substitution is prevalent along the MgSiO3 - MgAlO2.5 join. Oxide melt solution calorimetry has been used to compare the energetics of both substitutions. The stoichiometric substitution, represented by the reaction 0.95 MgSiO3 (perovskite) + 0.05 Al2O3 (corundum) = Mg0.95Al0.10Si0.95O3 (perovskite), has an enthalpy of-0.8±2.2 k J/mol. The nonstoichiometric reaction, 0.90 MgSiO3 (perovskite) + 0.10 MgO (rocksalt) + 0.05 Al2O3 (corundum) - MgS0.9A0.1O2.95 (perovskite) has a small positive enthalpy of 8.5±4.6 kJ/mol. The defect substitution is not prohibitive in enthalpy, entropy, or volume, is favored in perovskite coexisting with magnesiowüstite, and may significantly affect the elasticity, rheology and water retention of silicate perovskite in the Earth.

Original languageEnglish (US)
Pages (from-to)103-108
Number of pages6
JournalMaterials Research Society Symposium - Proceedings
Volume718
DOIs
StatePublished - 2002
Externally publishedYes
EventPerovskite Materials - San Francisco, CA, United States
Duration: Apr 1 2002Apr 5 2002

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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