The dielectric temperature characteristic of additives modified barium titanate having core-shell structured ceramics

The dielectric temperature characteristics and microstructures of BaTiO₃-based ceramics sintered with additives such as Sm₂O₃, CeO₂, and Bi₂O₃:Nb₂O₅ were investigated using TEM, XRD, and EDS. For a Sm₂O₃-modified BaTiO₃ ceramic whose additives were uniformly distributed in grains, the ferroelectric transition temperature (T_c) was shifted to a lower temperature, while the transition temperatures (T₁ and T₂) were shifted to a higher temperature. The additions of CeO₂ and Bi₂O₃: PbO to BaTiO₃ formed the chemical inhomogeneity which was composed of grain core, grain shell, and concentration gradient region. The dielectric curve versus temperature of CeO₂-modified BaTiO₃ has the shape of one strong peak, whereas BaTiO₃ ceramics sintered with Bi₂O₃:Nb₂O₅ exhibit the broad dielectric constant at the low temperature region and 130 °C ferroelectric transition peak. The dielectric temperature characteristics of additives modified BaTiO₃ were determined in terms of the chemical inhomogeneity and stress induced by the difference of the unit cell volume between grain core and grain shell.