HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY STUDIES OF A NEAR SIGMA-11 GRAIN-BOUNDARY IN ALPHA-ALUMINA

The atomistic structure of a near Sigma 11 (N Sigma 11) grain boundary in ultrapure alpha-Al2O3 bicrystals was determined by quantitative hi gh-resolution transmission electron microscopy (HRTEM). High-resolutio n imaging revealed an atomically sharp interface with a characteristic periodic pattern at (0 $($) over bar$$ 111) parallel to (01 $$($) ove r bar 11) facets. The pattern was analyzed by comparing the HRTEM micr ographs with simulated images of different structures that had been re laxed by static-lattice calculations. The best agreement with experime nt was reached for the grain boundary structure with the lowest energy (1.7 J.m(-2)). Although this structure reproduces the relative transl ation 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.