Interfacial energies, local ionic coordinations and electronic states at basal twin interfaces in corundum were investigated by means of first-principles density-functional and empirical shell-model calculations. Three different metastable twin configurations were determined by using both theoretical approaches. These exhibited mirror, 2-fold-rotation and glide-mirror symmetries with respect to the basal interface planes. In all 3 metastable configurations, large changes in cation-cation coordination appeared in the interfacial regions, with the occurrence of additional (with respect to the bulk crystal) Al-Al nearest-neighbor pairs at very short distances on adjacent cation basal planes. Using both approaches, the rotation twin was found to have the lowest energy. This agreed with experimental high-resolution transmission electron microscopic observations. The calculated site-projected densities of states for interfacial O ions in the 3 twins were found to depend strongly upon the local O packing at the interfacial regions.

Interfacial Structures and Energetics of Basal Twins in α-Al2O3 - First-Principles Density-Functional and Empirical Calculations. A.G.Marinopoulos, S.Nufer, C.Elsässer: Physical Review B, 2001, 63[16], 165112 (9pp)