Effect of Fe doping on the structure and electric properties of relaxor type BSPT-PZN piezoelectric ceramics near the morphotropic phase boundary

The microstructure and electrical properties of Fe doped ternary complex piezoelectric ceramics 0.35BiScO3-0.6PbTiO3-0.05Pb(Zn1/3Nb2/3)O3-xFe (BSPT-PZN-xFe) with a composition near the morphotropic phase boundary were systematically investigated. The undoped BSPT-PZN showed a relaxor-like behavior. Addition of Fe largely reduced the diffuseness degree and improved the tetragonality. It also reduced the d33. The dielectric loss and the mechanical quality factor of the samples were, respectively, reduced and increased for about three times. The turning point in most of the parameters implies that the doping characteristics are mainly caused by the increased tetragonality (x < 0.4 mol%) or by the substitution induced defects (x > 0.4 mol%). Despite the complicated influence of Fe on the complex high temperature piezoelectric ceramics, it may still be used to significantly improve the 'hardness' of similar materials required for high power applications. Direct high temperature d33 measurements indicated a thermal depolarization temperature (250-260 °C) much lower than the peak value temperature (Tm ∼410-440 °C) in the temperature dependence of dielectric constant. This seems to be a challenge for the BSPT based ternary piezoelectric ceramics.