Observation of intergranular films in BaB₂O₄-added BaTiO₃ ceramics

Distribution characteristics of boundary phase in BaB₂O₄ added BaTiO₃ ceramics were investigated with a focus on the curvature difference of solid-liquid interfaces at two-grain and triple junctions. High-resolution transmission electron microscopy revealed that the triple junction of solid grains showed the positive curvature of solid-liquid interface and consisted of the mixture of liquid phase and crystallized BaB₂O₄ phase. On the other hand, flat amorphous thin film of 2.5-nm thickness was observed at the two-grain junction. This kind of boundary phase distribution characteristic was explained by the solubility difference between two kinds of junctions of solid grains that had different curvature of solid-liquid interfaces.