Charged oxygen interstitials in corundum: first principles simulations

Combining supercell models and hybrid B3PW exchange‐correlation functionals, ab initio simulations on quasi‐stable configurations of interstitial $O_i^-$ ions in α‐Al2O3 (corundum) crystals and possible migration trajectories have been modelled. We have studied crystalline distortion around migrating $O_i^-$ including interatomic distances and the effective atomic charges, as well as redistributions of the electronic density. Unlike neutral interstitial atom Oi studied by us previously, migrating $O_i^-$ ion does not form dumbbells with the nearest regular $O_{reg}^{q -}$ oxygen ions, due to the strong Coulomb interaction with the nearest $Al_{reg}^{q+}$ cations as well as stronger repulsion between $O_i^-$ and adjacent regular $O_{reg}^{q -}$ ions. We have also estimated the energy barrier for migration between the nearest quasistable configurations of interstitial $O_i^-$ ion. One of these configurations is an octahedron formed by six nearest $O_{reg}^{q -} $ anions in the centre of which $O_i^-$ ion is located, unlike a neutral Oi atom which prefers to migrate directly towards one of adjacent $O_{reg}^{q -} $ anions with the dumbbell formation. As the result, the barrier for $O_i^-$ ion migration in corundum has been found to be by ∼70% smaller than that of Oi atom. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)