Grain boundaries in material which contained an excess of 0.5, 0.3 or 0.1at%Ti, and had been sintered at 1300 or 1250C, were examined by means of scanning electron microscopy, electron back-scattering diffraction and transmission electron microscopy. In the 0.1%Ti excess material, large grains grew abnormally to form high-angle grain boundaries when they impinged. A large fraction of the grain boundaries was faceted in a hill-and-valley shapes. In the 0.5%Ti excess material, large grains which grew abnormally were elongated in the directions of their {111} double twins. These grains often formed flat grain boundaries which were parallel to their {111} planes with fine matrix grains. Grain-boundary segments between large impinging grains with high misorientation angles were also often parallel to the {111} planes of one of the grains. These grain boundaries were expected to be singular. Most of the grain boundaries between randomly oriented fine-matrix grains in the 0.3at%Ti excess material were also faceted, with hill-and-valley shapes at finer scales being observed under transmission electron microscopy. The facet planes were parallel to the {111}, {011} and {012} planes of one of the grain pairs, and were also expected to be singular. These high-angle grain boundaries, which lay on low-index planes of one of the grain pairs, were similar to those observed in other oxides and metals.

Faceting of High-Angle Grain Boundaries in Titanium-Excess BaTiO3. Y.K.Cho, D.Y.Yoon: Journal of the American Ceramic Society, 2004, 87[3], 438-42