Symmetrical Σ7 tilt grain boundaries in alumina were studied using bicrystals. Three types of Σ7 boundary were fabricated: rhombohedral twin, Σ7{1¯1•2}, and 2 types of [00•1] symmetrical tilt grain boundary with grain-boundary planes of {4¯5•0} and {2¯3•0}. These corresponded to Σ7{4¯5•0} and Σ7{2¯3•0}. Their atomic structures and grain-boundary energies were investigated by using high-resolution transmission electron microscopy and a thermal grooving technique, respectively. The high-resolution transmission electron microscopic observations showed that the Σ7{1¯1•2} boundary had a completely symmetrical atomic arrangement with respect to the grain-boundary plane. However, the Σ7{2¯3•0} and Σ7{4¯5•0} boundaries exhibited asymmetrical atomic structures which were confirmed by analyzing the atomic configurations using static-lattice calculations. Thermal grooving experiments showed that the grain-boundary energies depended strongly upon the properties of the grain-boundary planes.

Atomic Structures and Energies of Σ7 Symmetrical Tilt Grain Boundaries in Alumina Bicrystals. H.Nishimura, K.Matsunaga, T.Saito, T.Yamamoto, Y.Ikuhara: Journal of the American Ceramic Society, 2003, 86[4], 574-80