Temperature-Stable Dielectrics Based on Chemically Inhomogeneous BaTiO3

The dielectric properties and chemical homogeneity of BaTiO₃ ceramics sintered with additions of the pseudophase "CdBi₂Nb₂O₉" were investigated using SEM, TEM, STEM, and EDX. In materials showing the "X7R" dielectric temperature characteristic, the microstructure exhibits the grain core-grain shell structure. The perovskite material in the shell shows a temperature characteristic determined by mixed crystals of BaTiO₃ with the complex perovskites Ba(Bi_1/2Nb_1/2)O₃ and Ba(Cd_1/3Nb_2/3)O₃ having an approximate Curie point of -80°C. The chemical inhomogeneity emerges during a process of reactive liquid-phase sintering. Application of too-high sintering temperatures leads to uniform distributions of the additives via solid-state diffusion and to the loss of the X7R characteristic.