Grain boundary faceting and abnormal grain growth in BaTiO3

When 0.1 mol% TiO2-excess BaTiO3 was sintered below the eutectic temperatur e 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 we re faceted. On the other hand, however, when the air-sintered sample with f aceted grain boundaries was annealed in H-2, the faceted boundaries became defaceted, and the growth of abnormal grains was suppressed while the growt h of the matrix grains was enhanced, showing normal grain growth behavior. In addition, the abnormal grains that had been elongated along their twin l amella grew rather isotropically, irrespective of the presence of {111} twi ns. It appears therefore that {111} twins appear to enhance the growth of t he abnormal grains along the twin lamellae only when the grain boundary is faceted. After reannealing the H-2-annealed sample in air, however, the gra in growth behavior and grain boundary structure were found to recover those observed in the air-sintered sample. From these observations, it is conclu ded that abnormal growth of BaTiO3 grains observed is related to grain boun dary faceting and that boundary faceting is a necessary condition for abnor mal grain growth. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Sci ence Ltd. All rights reserved.