A sapphire bicrystal with a symmetrical Σ = 7 [0¯1•1]/180º grain boundary was fabricated by using a hot joining technique at 1500C. The stability of the grain boundary structure was evaluated by using a molecular orbital method, and the bond overlap population and net charge were calculated as a function of the interplanar distance between 2 adjacent grains across the grain boundary. As a result, the grain-boundary structure was deduced to be such that two O-terminated (01•2) planes were joined to each other at an interplanar distance of about 0.13nm. This result agreed well with the atomic grain boundary structure which was experimentally determined from high-resolution electron microscopic analysis.

Atomic Structure and Chemical Bonding State of Sapphire Bicrystal. Y.Ikuhara, T.Watanabe, T.Saito, H.Yoshida, T.Sakuma: Materials Science Forum, 1999, 294-296, 273-6