Point and small cluster defects in magnesium aluminate spinel were studied from a

first principles viewpoint. Typical point defects that occur during collision cascade

simulations were cation anti-site defects, which have a small formation energy and

were very stable, O and Mg split interstitials and vacancies. Isolated Al interstitials

were found to be energetically unfavourable but could occur as part of a split Mg–

Al pair or as a three atom–three vacancy Al 'ring' defect, previously observed in

collision cascades using empirical potentials. The structure and energetics of the

defects were investigated using density functional theory (DFT) and the results

compared to simulations using empirical fixed charge potentials. Each point defect

was studied in a variety of super-cell sizes in order to ensure convergence. It was

found that empirical potential simulations significantly overestimate formation

energies, but that the type and relative stability of the defects were well predicted

by the empirical potentials both for point defects and small defect clusters.

A Theoretical Study of Intrinsic Point Defects and Defect Clusters in Magnesium

Aluminate Spinel. C.A.Gilbert, R.Smith, S.D.Kenny, S.T.Murphy, R.W.Grimes,

J.A.Ball: Journal of Physics - Condensed Matter, 2009, 21[27], 275406