Non-stoichiometry in MgAl₂O₄ spinel

Abstract

Stoichiometric magnesium aluminate spinel, MgAl₂O₄, contains equimolar proportions of Al₂O₃ and MgO. Spinel can, however, exhibit significant deviations from this stoichiometric composition. There is considerable disagreement concerning which species compensate for either excess Al₂O₃ or MgO non-stoichiometry. Here, we use empirical and quantum mechanical (density functional theory) atomistic simulation techniques to investigate the defect chemistry accommodating non-stoichiometry. The incorporation of excess Al₂O₃ was found to be a lower energy process than the solution of excess MgO. Elevated magnesium and aluminium cation vacancy defect concentrations are predicted in Al₂O₃ rich spinels, whilst MgO excess is facilitated by a combination of oxygen vacancy and magnesium interstitial defects.

Keywords:

• non-stoichiometry
• spinel
• atomistic simulation
• defect structures

Acknowledgements

This work was carried out as part of the UKERC materials programme. Computational resources were provided by the Imperial College High Performance Computing Service (http://www.imperial.ac.uk/ict/services/teaching-andresearchservices/highperformancecomputing).