The atomic structure of asymmetric [001] tilt boundaries in SrTiO3

The atomic structures of 25 degrees and 45 degrees asymmetric [001] tilt boundaries in SrTiO3 have been determined experimentally using the unique combination of high-resolution Z-contrast imaging and simultaneous electron-energy-loss spectroscopy in the scanning transmission electron microscope. These complementary techniques permit the direct location of the cation columns at the boundary to an accuracy of 0.2 Angstrom and the coordination of the O atoms to be investigated with atomic resolution. Using bond-valence sum calculations, the structural and electronic results were combined to produce models for the grain-boundary structures. These calculations highlighted the presence of half-occupied columns at both grain boundaries as an important feature for reducing the grain-boundary energy associated with these ionic materials. In addition, the grain-boundary structure units identified in the experimental images were used to predict structures for other misorientations by the application of the principles of continuity of grain-boundary structure.