It was recalled that a complex which consisted of a trivalent Fe ion in a cube-center interstitial site, tetrahedrally coordinated with four Ag vacancies and 4 halogen ions, had been detected in AgCl by means of electron paramagnetic resonance studies. Here, perturbed angular correlation spectroscopy was used to detect a similar defect complex of

In3+ in AgCl and AgBr. In some samples, there was an increase in the fraction of 111In3+ ions in cubo-symmetrical sites. The rate and temperature at which this conversion occurred varied from sample to sample. It was concluded that there was only one possible attribution for this cubo-symmetrical defect center that was consistent with previous data: a negatively charged configuration. It was argued that the stability of this defect was explicable on purely ionic grounds. The tetrahedral defect vanished at 250K in AgCl and at 200K in AgBr. In AgCl, the tetrahedral defect persisted when the temperature was lowered to below the formation temperature. In the case of AgBr, a decrease in temperature caused the defect center to revert back, at least partially, to the usual low-temperature configuration.

J.C.Austin, M.L.Swanson: Journal of Physics - Condensed Matter, 1995, 7[50], 9747-54