INFLUENCE OF STOICHIOMETRY AND IMPURITY ON THE SINTERING BEHAVIOR OF BARIUM-TITANATE CERAMICS

Abstract

The influence of stoichiometry, i.e. Ba/Ti ratio, and impurity on the densification of BaTiO3 were investigated. The BaTiO3 powders were prepared by conventional calcination of BaCO3 and TiO2. The stoichiometric ratios (Ba/Ti) were in the range 0.99 to 1.005. Impurity effects on the sintering behaviour were investigated with different purities of raw powders. The sintering behaviour of BaTiO3 has been studied extensively but an understanding of stoichiometric effects on densification is still incomplete. An excess of TiO2 lowered the onset temperature of sintering (initial state of sintering - 3% shrinkage). These results indicate that stoichiometric variation of BaTiO3 affects the initial state of sintering. The rate of densification for a Ti-rich sample was considerably faster than that for a Ba-rich sample. It was a so-called "activated" sintering. The TiO2 excess reacts with BaTiO3 to form Ba6Ti17O40, which forms with BaTiO3 a eutectic melt at 1320-degrees-C. The liquid phase, however, enhanced grain growth, not densification.