DFT study of migration enthalpies in MgSiO₃ perovskite

Authors: Ammann, M.¹; Brodholt, J.²; Dobson, D.²

Source: Physics and Chemistry of Minerals, Volume 36, Number 3, March 2009 , pp. 151-158(8)

Publisher: Springer

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Abstract:

The effect of pressure on ionic diffusion in orthorhombic MgSiO₃ perovskite has been investigated using density functional theory. An intensive investigation of possible silicon pathways revealed new positions of the saddle-points and an enthalpy of migration at 26.2 GPa of 4.7 eV that is in fair agreement with the experimental values of about 3.5 eV at 25 GPa. This is much lower than found in previous studies (~9 eV) and removes the need to explain silicon diffusion by a complicated process involving coupled oxygen vacancies, as has been previously proposed. Our migration enthalpies for oxygen and magnesium are in excellent agreement with experiments. We find that oxygen diffusion occurs via a chain of several inequivalent jumps along the octahedron edges, and that magnesium occurs via two inequivalent [110] jumps and one [001] jump. We also present activation volumes for all three species at 25 and 135 GPa.

Keywords: Migration enthalpies; MgSiO3 perovskite; High pressure; Rheology of lower mantle

Document Type: Research article

DOI: http://dx.doi.org/10.1007/s00269-008-0265-z

Affiliations: 1: Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK, Email: m.ammann@ucl.ac.uk 2: Department of Earth Sciences, University College London, Gower Street, London, WC1E 6BT, UK

Publication date: 2009-03-01