Atomic Structure of Symmetric Tilt Grain Boundaries in NiO

High-resolution electron microscopy shows the coexistence of several distinct core structures for coincident-site lattice boundaries in NiO bicrystals near =5, (310), and =13, (510), where is the reciprocal density of coincident lattice sites. Lattice expansion perpendicular to the =5 grain boundaries is considerably smaller than calculated theoretically. Structural units in boundaries near =13, (510) exhibit translations normal to the grain-boundary plane, resulting in a rumpling of the interface on an atomic scale. Our observations suggest the presence of a high concentration of Schottky pairs in the grain boundaries.