Interstitial faulted dislocation dipole formation in sapphire (α-Al2O3)

While both vacancy and interstitial edge-trapped perfect dislocation dipoles form with equal probability during high temperature basal deformation of sapphire, faulted dipoles are invariably interstitial in character. The most likely origin of this asymmetry is the different energy associated with the point defects needed to be ejected into the bulk crystal for a dipole to be annihilated. Interstitial point defects are much more energetic than vacancy defects, leading to immediate supersaturation, and rapid condensation of the interstitials into a faulted dipole segment, rather than being absorbed by the bulk crystal.