Atomic Structure of Tilt Grain Boundaries in NiO

Abstract

High-resolution electron microscopy at 400 kV has been used to study the core structure of large-angle tilt grain boundaries in NiO. The deduced atomic structures show considerable variety and complexity, even for boundaries with the same tilt axis and misorientation. The coexistence of asymmetric and symmetric boundaries which is observed at each misorientation suggests that asymmetric grain boundaries containing densely packed planes are associated with relatively low free energies. A multiplicity of core structures is found for the =5 and the =13 grain boundaries. The normal component of the rigid-body translation in these boundaries is quite small in view of the relatively open structure that is expected for grain boundaries in ionic solids. Substantial concentrations of Schottky pairs near the boundary cores, as well as relaxations parallel to the misorientation axis, are indicated. 11 refs., 7 figs.