Defect simulation procedures were applied to doped spinels and intrinsic defects which originated from cation antisite disorder, due to partial interchange of the positions of divalent and trivalent cations, were studied. It was found that the probability of Al3+ replacing Mg2+ was higher than the reverse process. The simulation results indicated that the configurational energy was lower for Al3+ being replaced by trivalent impurities (Cr3+, Mn3+, Co3+) than for the replacement of Al3+ by divalent impurities (Cr2+, Mn2+, Co2+); thus questioning the existence of impurity-vacancy dipoles. The thermally stimulated depolarisation current spectra of the spinels contained bands at 120, 160, 250 and 300K. The presence of these bands varied from sample to sample, and some crystals did not exhibit any of the bands. The 160 and 250K bands were suggested to be of dipolar origin and γ-irradiation to upto 1.5kGy enhanced the 250K peak in samples that already exhibited it. It created a 250K peak in samples that did not exhibit it before irradiation.

Computer Modelling in MgAl2O4 Spinels. S.S.De Souza, F.A.De Oliveira Neto, A.R.Blak: Radiation Effects and Defects in Solids, 1999, 151[1-4], 1015-9