Growth kinetics of interstitial loops in irradiated sapphire

The growth of interstitial dislocation loops that occurs on annealing oxygen ion-irradiated sapphire is interpreted in terms of a simple statistical model, based on the random diffusion of excess interstitial ions to existing dislocation loops. The growth of the loops is characterized by an activation energy of 1·86±0·1 ev which is thought to be that for interstitial migration of oxygen ions. It is shown that excess interstitial ions are retained in the foils for anomalously long times during annealing. This is interpreted in terms of the combined effect of a charge double layer at the surface of the platelets and anisotropy of the interstitial diffusion coefficients. Coalescence of the loops by the ‘self-climb’ mechanism is found to be an important factor in loop growth when the loop density is high.