A computational model of cation ordering in the magnesioferrite-qandilite (MgFe2O4-Mg2TiO4) solid solution and its potential application to titanomagnetite (Fe3O4-Fe2TiO4)

Harrison, Richard J. and Palin, Erika J. and Perks, Natasha (2013) A computational model of cation ordering in the magnesioferrite-qandilite (MgFe2O4-Mg2TiO4) solid solution and its potential application to titanomagnetite (Fe3O4-Fe2TiO4). American Mineralogist, 98 (4). pp. 698-708. ISSN 0003-004X DOI https://doi.org/10.2138/am.2013.4318

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Abstract

Cation ordering in the magnesioferrite-qandilite (MgFe2O4-Mg2TiO4) solid solution has been investigated using an interatomic potential model combined with Monte Carlo simulations. The dominant chemical interaction controlling the thermodynamic mixing behavior of the solid solution is a positive nearest-neighbor pairwise interaction between tetrahedrally coordinated Fe3+ and octahedrally coordinated Ti4+ (JTFeOTi). The predicted cation distribution evolves gradually from the Néel-Chevalier model to the Akimoto model as a function of increasing JTFeOTi, with JTFeOTi = 1000 ± 100 K providing an adequate description of both the temperature and composition dependence of the cation distribution and the presence of a miscibility gap. Although Mg is a good analog of Fe2+ in end-member spinels, a comparison of model predictions for MgFe2O4-Mg2TiO4 with observed cation ordering behavior in titanomagnetite (Fe3O4-Fe2TiO4) demonstrates that the analog breaks down for Fe3O4-rich compositions, where a value of JTFeOTi closer to zero is needed to explain the observed cation distribution. It is proposed that screening of Ti4+ by mobile charge carriers on the octahedral sublattice is responsible for the dramatic reduction in JTFeOTi. If confirmed, this conclusion will have significant implications for attempts to create a realistic thermodynamic model of titanomagnetite.

Item Type:	Article
Uncontrolled Keywords:	2013AREP; IA65;
Subjects:	03 - Mineral Sciences 06 - Part-III Projects
Divisions:	06 - Part-III Projects
Journal or Publication Title:	American Mineralogist
Volume:	98
Page Range:	pp. 698-708
Identification Number:	https://doi.org/10.2138/am.2013.4318
Depositing User:	Sarah Humbert
Date Deposited:	25 May 2013 13:09
Last Modified:	17 Feb 2017 13:06
URI:	http://eprints.esc.cam.ac.uk/id/eprint/2792

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