First-principles pseudopotential calculations using plane-wave basis functions were made to evaluate quantitatively the formation energy of Cr/Al vacancies in MgCr2O4 and MgAl2O4. Relaxation of the atoms within the second-nearest neighbor shell of the vacancy was taken into account in a 56-atom super-cell. The formation energy was calculated as a function of the atomic chemical potential of Cr/Al. It showed negative values in the case of the oxidation limit of MgCr2O4, which was in good agreement with experimental results showing abundance of Cr vacancies when annealed in air. The formation energy of the Al vacancy in MgAl2O4, under the same conditions, was as large as 4.76eV. This reflected the fact that MgAl2O4 did not form the Al vacancy alone in air.

Formation Energy of Cr/Al Vacancies in Spinel MgCr2O4 and MgAl2O4 by First-Principles Calculations. H.Moriwake, I.Tanaka, F.Oba, Y.Koyama, H.Adachi: Physical Review B, 2002, 65[15], 153103