The formation process of BaTiO3 from powder compacts, equi-molar mixture of BaCO3 and TiO2, and an abnormal expansion during the formation process were investigated. The formation process of BaTiO3 from BaCO3 and TiO2 is devided into three steps. In the microscopic observation, it was confirmed that a powder compact of BaCO3 on magnesia and rutile substrates begins to melt at 950degreesC. This liquid phase is thought to influence the formation reaction of BaTiO3 greatly. It is well known that Ba component diffuse to TiO2 one-sidedly in this reaction. As a result, the space where BaCO3 occupied in a compact specimen is left as a pore after the reaction has teminated, and the change of TiO2 particles to BaTiO3 particles results in a volume expansion of the compact. These are considered to be the cause of an abnormal expansion during the reaction of BaCO3 and TiO2.
