Ab initio simulations on migration paths of interstitial oxygen in corundum

Ionizing radiation produces in Al2O3 (corundum) crystals primary Frenkel pairs of complementary defects (in oxygen sublattice these are oxygen vacancies and interstitial oxygen ions, VO−Oi). The interstitial Oi atoms begin to migrate above certain temperature and create the dumbbell pairs with regular oxygen atoms (Oreg−Oi). We have calculated the optimal dumbbell configurations and optimized further migration paths (i.e., Oi interstitial can break the bond with one Oreg atom and moves towards another, one of four next-neighbor Oreg atoms). To simulate all possible Oi migration trajectories, we have performed large-scale hybrid DFT-LCAO PBE0 calculations on 2×2×1 supercells of defective α-Al2O3 crystals using CRYSTAL14 computer code. The limiting barrier height for oxygen interstitial 3D migration is estimated as 1.3eV.