Microstructure of BaTiO₃–Bi(Mg_1/2Ti_1/2)O₃–BiFeO₃ Piezoelectric Ceramics

The dependence of the ferroelectric and piezoelectric properties of (1-x)(0.33BaTiO₃–0.67BiFeO₃)–xBi(Mg_1/2Ti_1/2)O₃ (x = 0, 0.05, 0.10, and 0.15) on Bi(Mg_1/2Ti_1/2)O₃ content x associated with microstructural changes is studied. From the behaviour of electric field-induced polarization and strain, polarization switching and depolarizing become easier as Bi(Mg_1/2Ti_1/2)O₃ content x increases. Remanent polarization and dielectric constant decrease, while polarization saturation field increases with increasing x. Microstructural observation reveals that Bi(Mg_1/2Ti_1/2)O₃ addition enhances the compositional fluctuation of BaTiO₃/BiFeO₃ ratio, which probably creates a nanometre-sized domain region with slightly BaTiO₃-rich composition. Since this nanometre-sized domain may cause relatively large responses of polarization and strain to the applied electric field, an appropriate amount of Bi(Mg_1/2Ti_1/2)O₃ enhances the electric field-induced strain, resulting in the largest piezoelectric response at x = 0.05. However, excessive Bi(Mg_1/2Ti_1/2)O₃ degrades polarization and strain characteristics, because a number of Ba(Fe_1-xMg_x/2Ti_x/2)₁₂O₁₉ grains are created as a secondary phase and cause the segregation of excess bismuth oxide phases with low dielectric constant into the boundaries of the ferroelectric/piezoelectric grains.