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Effects of high pressure and high temperature on cation ordering in magnesioferrite, MgFe₂O₄, using in situ synchrotron X-ray powder diffraction up to 1430 K and 6 GPa

¹ Mineral Physics Institute and Department of Geosciences, State University of New York, Stony Brook, New York 11794-2100, U.S.A.
² Department of Chemistry, University of the West Indies, Mona, Kingston 7, Jamaica
³ European Synchrotron Radiation Facility, BP 220, F 38043 Grenoble, France

Correspondence: ^* E-mail sytle.antao{at}stonybrook.edu

Disorder in stoichiometric magnesioferrite, MgFe₂O₄, was determined from in situ synchrotron powder X-ray diffraction data [ = 0.3738(4) Å] at 6, 5, and 3 GPa and temperatures up to 1430 K. The a unit-cell parameter increases linearly on heating at the three different pressures. Higher pressures cause a smaller cell volume, as expected. Cation order was analyzed in terms of the inversion parameter, x, {^iv[Mg_1–xFe_x]^vi[Mg_x/2Fe_1–x/2]₂O₄} and the order parameter Q = 1 – (3/2)x. As pressure increases, the inversion parameter increases in inverse MgFe₂O₄ spinel. O’Neill and Navrotsky (1983) and Landau models were used to describe the equilibrium non-convergent ordering process in MgFe₂O₄, and they both fit the data well.