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The dielectric properties and chemical homogeneity of BaTiO 3 ceramics sintered with additions of the pseudophase “CdBi 2 Nb 2 O 9 ” 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 BaTiO 3 with the complex perovskites Ba(Bi 1/2 Nb 1/2 )O 3 and Ba(Cd 1/3 Nb 2/3 )O 3 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.
Hennings et al. (Sun,) studied this question.