Structure, relaxation behaviors and nonlinear dielectric properties of BaTiO₃-Bi(Ti_0.5Mg_0.5)O₃ ceramics

(1-x)BaTiO₃-xBi(Mg_1/2Ti_1/2)O₃ (BT-BMT, x=0-0.2, abbreviated as BT-BMT100x) ceramics were prepared by using a solid state reaction process. Their crystal structure, microstructure, conduction behavior, dielectric and tunability properties were investigated. It is found that the tetragonal phase and a pseudocubic phase coexist for x≤0.15 and transform to a pseudocubic phase at x=0.20. With the incorporation of BMT, BT-BMT becomes more insulating. The activation energies of the conduction are respectively 1.15(1) and 1.54(1) eV for grain and grain boundary of BT-BMT20. Furthermore, an abnormal nonlinear dielectric tunable behavior is observed. The dielectric permittivity first slightly increases until reaching the threshold electric field, and then suddenly decreases. This abnormal nonlinear dielectric behavior is attributed to the synergetic effects of the clamped oxygen vacancies and excessive aggregation of Bi at the grain boundaries.