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Cation distribution and mixing thermodynamics in Fe/Ni thiospinels

Haider, S; Grau-Crespo, R; Devey, AJ; de Leeuw, NH; (2012) Cation distribution and mixing thermodynamics in Fe/Ni thiospinels. Geochimica et Cosmochimica Acta , 88 275 - 282. 10.1016/j.gca.2012.04.007. Green open access


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The structural analogy between Ni-doped greigite minerals (Fe3S4) and the (Fe, Ni)S clusters present in biological enzymes has led to suggestions that these minerals could have acted as catalysts for the origin of life. However, little is known about the distribution and stability of Ni dopants in the greigite structure. We present here a theoretical investigation of mixed thiospinels (Fe1−xNix)3S4, using a combination of density functional theory (DFT) calculations and Monte Carlo simulations. We find that the equilibrium distribution of the cations deviates significantly from a random distribution: at low Ni concentrations, Ni dopants are preferably located in octahedral sites, while at higher Ni concentrations the tetrahedral sites become much more favourable. The thermodynamic mixing behaviour between greigite and polydymite (Ni3S4) is dominated by the stability field of violarite (FeNi2S4), for which the mixing enthalpy exhibits a deep negative minimum. The analysis of the free energy of mixing shows that Ni doping of greigite is very unstable with respect to the formation of a separate violarite phase. The calculated variation of the cubic cell parameter with composition is found to be non-linear, exhibiting significant deviation from Vegard’s law, but in agreement with experiment.

Type: Article
Title: Cation distribution and mixing thermodynamics in Fe/Ni thiospinels
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.gca.2012.04.007
Publisher version: http://dx.doi.org/10.1016/j.gca.2012.04.007
Language: English
Additional information: This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
URI: http://discovery.ucl.ac.uk/id/eprint/1352531
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