Abnormal grain growth kinetics BaTiO3 with an excess TiO2

The abnormal grain growth of BaTiO3 containing an excess of 0.1, 0.2, and 0.4 mol% of TiO2 is studied. It is found that the matrix grain size depends on TiO2 excess but does nor change with annealing temperature or time characterizing that the matrix grain growth is strongly suppressed. The number of abnormal grains per unit of volume also behaves in a similar way indicating that the abnormal grains originated right in the beginning of the reaction in a situation analogous to a site-saturated transformation. The evolution of the volume fraction of the abnormal grains with time has an unusual feature: the maximum volume fraction, for a given TiO2 excess, is less than one for lower annealing temperatures but increases with annealing temperature. A model is proposed to describe the kinetics that agrees well with measured data. Abnormal grain growth has been confirmed to occur in the solid state below the eutectic temperature. Nonetheless both experimental and theoretical results suggest that abnormal grain growth kinetics is significantly faster above the eutectic temperature. The nature of the pinning force in BaTiO3 containing an excess of TiO2 is also discussed in detail. (C) 1998 Acta Metallurgica Inc.