Structure of grain boundaries in ceramics

Abstract

Grain boundaries in different ceramics were studied. Quite frequently, an amorphous film can be detected on the grain boundaries. The amorphous layer should invalidate all geometrical description of a “clean” boundary, e.g. the coincidence size lattice (CSL) and the DSC lattice. Usually, this amorphous layer forms during densification which often occurs by a liquid phase sintering process. Well defined small-angle and large-angle grain boundaries in Ni 1− y O show that a region of reduced mean inner potential (compared to the perfect lattice) exists at the boundaries. The reduction in mean inner potential can be caused by (i) the dilatation in the core region of grain boundary dislocations, (ii) a net charge at the boundary, (iii) change in composition at the boundary and (iv) by segregation of impurities. The contributions of the different effects are discussed.