Nonstoichiometry of magnetite-ulvospinel solid solutions quenched from 1300°C

E. Senderov, A. U. Dogan, A. Navrotsky

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27 Scopus citations

Abstract

Magnetite-ulvospinel (Fe3O4-Fe2TiO4) solutions were synthesized in CO2 + H2 atmospheres and quenched from 1300°C to liquid N2. The fO2 during synthesis was monitored by a solid electrolyte cell. The samples obtained under relatively reducing conditions at the boundary with fields containing wustite or metallic Fe have systematically higher ao values than ulvospinel coexisting with rhombohedral solid solutions or synthesized near this boundary under relatively oxidizing conditions. The change in a0 across the solid-solution field at a fixed Ti/Fe ratio becomes more pronounced and approaches 0.01 Å for high Ti compositions. The unit-cell parameter variation at a constant Ti/Fe ratio is related to the deviation from stoichiometry [(Fe + Ti)/O < 3/4 ] of the solution Fe3-xTixO4+y. Trends were obtained in the cation to O ratio with increasing fO2 at fixed Ti/Fe by direct O analysis using the electron microprobe. A gain of approximately 2 mol% O (y = 0.08) for quenched samples with a x≥ 0.7 under the most oxidizing conditions is seen relative to samples quenched under reducing conditions and assumed to be stoichiometric (y = 0). A phase diagram in x - fO2 space at 1300°C is presented. -from Authors

Original languageEnglish (US)
Pages (from-to)565-573
Number of pages9
JournalAmerican Mineralogist
Volume78
Issue number5-6
StatePublished - 1993
Externally publishedYes

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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