Static-lattice calculations of the energies and structures of (101n) (n = 0, 1, and 4) and (0001) grain boundaries in a-Al,O, using three different potentials are reported. It was found that the energies of boundaries perpendicular to the (W1) direction vary between 0.3 and 0.9 J-m-'. These compare favorably to experimental values, and the results are not sensitive to the choice of potential. The energies of the other boundaries do depend on the potential, but their relaxed structures do not. Using the most reliable potential, the energies of boundaries which have been studied by highresolution electron microscopy range from 1.0 to 1.7 J.m-*. Simulated images of the calculated structures compare favorably with high-resolution electron microscope micrographs of these boundaries.
The atomistic structure of a near 211 (N211) grain boundary in ultrapure cu-Al,O, bicrystals was determined by quantitative high-resolution transmission electron microscopy (HRTEM). High-resolution imaging revealed an atomicallesharp interface with a characteristic periodic pattern at (0111) I] (0111) facets. The pattern was analyzed by comparing the HRTEM micrographs with simulated images of different structures that had been relaxed by static-lattice calculations. The best agreement with experiment was reached for the grain boundary structure with the lowest energy (1.7 J.m-'). Although this structure reproduces the relative translation state of the adjacent crystals to within 0.02 nm, the calculated structure was not in complete agreement with the periodic pattern at the grain boundary. The origin of this difference is probably due to a slight misalignment of the two crystals adjacent to the boundary.
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