Local interfacial structures and bonding at the rhombohedral twin interface in corundum were studied by means of first-principles electronic structure calculations which were based upon local density functional theory. Two sets of geometrical interface models were selected. One of them assumed the presence of a terminating O layer at the interface. The other assumed the termination, of the corundum structure, by interstitial vacancies. Optimum interface configurations were obtained by minimizing the total internal energy with respect to relative translation states of the adjoining grains and relaxations of all of the atomic positions. These were a vacancy-terminated configuration with a very low interface energy, a well-defined relative translation state with screw-rotation symmetry and a highly ordered atomic structure which minimized the mutual repulsion between neighboring like-charged ions. A second metastable configuration, with vacancy termination and a higher interface energy, was also obtained as well as a metastable O-terminated structure with an interface energy which lay between those of the 2 vacancy-terminated configurations. Theoretical results for the interfacial structures and translation states were considered with respect to experimental investigations of the twin interface via high-resolution transmission electron microscopy. The calculated interfacial site-projected densities of electron states exhibited significant deviations from the bulk-crystal projected densities of electron states in the conduction bands.

Microscopic Structure and Bonding at the Rhombohedral Twin Interface in α-Al2O3. A.G.Marinopoulos, C.Elsässer: Acta Materialia, 2000, 48[18-19], 4375-86