Dielectric Properties in BaTiO₃-BaSnO₃ and BaTiO₃-Ba(Fe1/2Ta1/2)O₃ Systems

Complete solid solutions with perovskite type structures were formed in systems of BaTiO 3 -BaSnO 3 and BaTiO 3 -Ba(Fe 1/2 Ta 1/2 )O 3 . The Curie temperature of the BaTiO 3 -BaSnO 3 system decreased linearly with BaSnO 3 content and the relation between the Curie constant and the Curie temperature was also linear with a tangent of 3.3×10 2 . The broad phase transition in this system was attributed to simultaneous occurrence of composition fluctuations and weak ferroelectric interactions. In the BaTiO 3 -Ba(Fe 1/2 Ta 1/2 )O 3 system, the Curie temperature decreased rapidly whereas the Curie constant increased with increasing Ba(Fe 1/2 Ta 1/2 )O 3 content. The relation of Curie constant versus Curie temperature was approximately linear with a negative tangent of -1.3×10 2 . The broader phase transition in the BaTiO 3 -Ba(Fe 1/2 Ta 1/2 )O 3 system was ascribed to a direct disturbance of interactions between the permanent electric dipoles caused by local ion pairs. The anomalous increase in the Curie constant was attributed to an increase of electron deformation due to the existence of nonisovalent B ions.