Investigation Of High Performance High Curie Temperature Piezoelectric Ceramics

There are a few of high Curie temperature piezoelectric ceramics, which have excellent properties and high operating temperature. However, it is used widely. In this work, preparation and characterization of perovskite high Curie temperature piezoelectric ceramics (mainly with modified PbTiO₃ piezoelectric ceramics) were investigated. All ceramics have been processed by conventional sintering from ceramics powders synthesized by one step, direct solid-state reaction of the constituent oxides.First, La and MnO₂-modified Bi(Mg_1/2Ti_1/2)O₃-PbTiO₃ were prepared and studied. All samples have pure perovskite phase. The grain size become smaller and uniform, the Curie temperature and peak of dielectric constant become decreased and dielectric anomaly gradually disappears with increasing of La-doped. The coercive field and remanent polarization are decreased with increased La-doped and the same content of PbTiO₃. It is favorable to ceramic sintering and growing of grain for MnO₂-modified. Meanwhile, the peak of dielectric constant, coercive field, remanent polarization and piezoelectric properties (6pC/N) decreased, but Curie temperature(higher than 600℃) improved from dielectric permittivity-temperature dependence and corresponding polarization-field hysteresis loop.Second, Fe-doped Bi(Mg_1/2Ti_1/2)O₃-PbTiO₃ were prepared and investigated. The tetragonality of samples decreased. The dielectric constants decreased and dielectric losses are increased with improving of frequency, Curie temperature of some samples are increased from dielectric permittivity-temperature dependence. The coercive field and remanent polarization are decreased and cannot get into saturation state at room temperature. They are also decreased but easily get into saturation state at 120℃. The samples of B(MT)_0.95F_0.05-0.39PT, B(MT)_0.90F_0.10-0.37PT and B(MT)_0.90F_0.10-0.39PT have good piezoelectric properties (higher than 150pC/N) by depolarization treatment at 420℃. The domain size becomes small with increasing of content PbTiO₃. Impedance of samples are gradually decreased with increasing of test temperature, grain boundary and grain make the same contribution for the resistance.Last, different compositions of (1-x)Bi(Mg_2/3Nb_1/3)O₃-xPbTiO₃ are successfully prepared by the solid state reaction technology. It is tetragonal phase when x≥0.7, while it is rhombohedral phase when x＜0.6. Therefore, the morphotropic phase boundary near x=0.6. It is diffuse phase transition when x≥0.7, while the samples of x=0.6, 0.5 is frequency dispersion. The peak of dielectric constant and loss are decreased and the peak location shift from high to low temperature with increasing of frequency when the content of PbTiO₃ is decreased. The composition of x=0.9, 0.5 are the second order phase transition ferroelectrics, while composition of x=0.8, 0.7, 0.6 are the first order. The dispersivity of samples is decreased with increasing of content PbTiO₃ according to dispersivity index. Impedance of samples is gradually decreased with increasing of test temperature. The domain of BMN-0.8PT is strip form with about 0.5um of width, bright-dark interphase.