The rhombohedral twin orientation in alumina was obtained by using diffusion-bonding and was studied by means of transmission electron microscopy. It corresponded to a Σ = 7 near-coincidence orientation, with a grain boundary plane parallel to (01•2). The grain boundary contained 2 arrays of dislocations having the same line direction and alternately distributed Burgers vectors which were translation vectors of the DSC lattice. The associated step vectors were large (up to 1.75nm). Starting from symmetry considerations of the various dichromatic complexes, all of the possible unrelaxed atomic configurations were constructed. The O-terminated grain-boundary structures, as well as those passing through non-occupied Al sites were selected on the basis of optimal compactness at the interface. Correlations between the simulated and experimental high-resolution images favored those structures which were based upon empty octahedral sites at the interface. The most probable structure had a 2-fold screw axis at the interface, and left Al-O bonds with very little distortion with respect to the perfect coordination in alumina.

Near Coincidence Grain Boundary in Alumina. S.Lartigue-Korinek, S.Hagège: Materials Science Forum, 1999, 294-296, 281-4