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Abstract
Tables are given of all coincidence orientations with multiplicity Σ ≤ 36 for rhombohedral lattices with axial ratios in the range of corundum type structures (2.696 < c/a < 2-765). Measurements of the relative orientation of 133 pairs of neighbouring grains in sintered a-alumina showed that near-coincidence boundaries (14 cases) and one-dimensional coincidence boundaries (17 cases) occurred more frequently than would be the case for randomly distributed orientations and that many of these special boundaries contained periodic arrays of grain boundary dislocations. Their Burgers vectors have been determined for a rhombohedral twin boundary in order to decide which one among three possible coincidence descriptions best represents the boundary structure.
