Grain boundary faceting and abnormal grain growth in BaTiO3 Original Research Article

When 0.1 mol% TiO2–excess BaTiO3 was sintered below the eutectic temperature in air, abnormally large grains formed in the fine matrix BaTiO3 grains. The abnormal grains contained {111} twin lamellae, while the matrix grains did not. A TEM observation revealed that almost all the grain boundaries were faceted. On the other hand, however, when the air-sintered sample with faceted grain boundaries was annealed in H2, the faceted boundaries became defaceted, and the growth of abnormal grains was suppressed while the growth of the matrix grains was enhanced, showing normal grain growth behavior. In addition, the abnormal grains that had been elongated along their twin lamella grew rather isotropically, irrespective of the presence of {111} twins. It appears therefore that {111} twins appear to enhance the growth of the abnormal grains along the twin lamellae only when the grain boundary is faceted. After re-annealing the H2-annealed sample in air, however, the grain growth behavior and grain boundary structure were found to recover those observed in the air-sintered sample. From these observations, it is concluded that abnormal growth of BaTiO3 grains observed is related to grain boundary faceting and that boundary faceting is a necessary condition for abnormal grain growth.