The atomic structures of 25 and 45 asymmetrical [001] tilt boundaries were determined experimentally by using an unique combination of high-resolution Z-contrast imaging and simultaneous electron energy-loss spectroscopy in a scanning transmission electron microscope. These complementary techniques permitted the direct location, of cation columns at the boundary, to an accuracy of 0.02nm. The coordination of the O atoms could also be investigated at atomic resolution. By using bond valence sum calculations, the structural and electronic results were combined so as to produce models of the grain-boundary structures. These calculations revealed that the presence of half-occupied columns at both grain boundaries was an important factor in the reduction of the grain-boundary energy that was associated with these ionic materials. The grain-boundary structural units which were identified in the experimental images were used to predict the structures, for other misorientations, by applying the principle of continuity of the grain-boundary structure.

M.M.McGibbon, N.D.Browning, A.J.McGibbon, S.J.Pennycook: Philosophical Magazine A, 1996, 73[3], 625-41