High-resolution transmission electron microscopy and computational analyses of atomic structures of [0001] symmetric tilt grain boundaries of Al2O3 with equivalent grain-boundary planes

Al2O3 bicrystals containing [0001] symmetric tilt grain boundaries were fabricated to investigate atomic structures at their grain-boundary cores. Sigma7 and Sigma21 boundaries studied here have crystallographically equivalent grain-boundary planes of {2 (3) over bar 10}parallel to{21 (3) over bar0}, although they have different Sigma values. Grain-boundary structures were studied by high-resolution transmission electron microscopy (HRTEM) and static lattice calculations based on ionic potentials. HRTEM observations showed that the Sigma7 and Sigma21 boundaries exhibited asymmetric core structures with respect to their grain-boundary planes. From static lattice calculations, it was found that these two grain boundaries have similar rigid-body shifts normal to the tilt axis and also contain open spaces at their core. The similarity of their core structures indicates that characteristics of grain-boundary cores strongly depend on features of grain-boundary planes.