Structures and properties of the Sb-doped PLZT ferroelectric ceramics around the morphotropic phase boundary

Abstract

For the applications of piezoelectric energy harvester, both a large figure of merit and a high Curie temperature are required for ferroelectric ceramics. In this work, the Sb-doped PLZT (Pb_0.96La_0.04(Zr_1-xTi_x)O₃ + 0.5 wt.%Sb₂O₅) ceramics were synthesized by the conventional solid-state reaction process, and the compositional dependence of phase structures, microstructure and electrical properties were comprehensively investigated. Firstly, the manipulable R-T morphotropic phase boundary (MPB) has been successfully built by adjusting the Zr/Ti ratio, and the shift of MPB is found to significantly influence the dielectric properties and ferroelectric modes of the Sb-doped PLZT ceramics. The reduced polarization anisotropy in the MPB region provides a driving force for abnormal grain growth. Moreover, the presence of oxygen vacancies was verified in the ceramics by the X-ray photoelectron spectroscopy measurement. In particular, the ferroelectric properties and domain switching of the ceramics were analyzed in detail from the P-E and J-E hysterisis loops measured at different temperatures and electric fields. The internal bias field E_i increased with rise in temperature, as evidenced by the high concentration of oxygen vacancies identified in the sample with x = 0.47. The intrinsic relaxation phenomenon observed in the domain switching process was attributed to the short-range migration of singly ionized oxygen vacancies at elevated temperatures. With increasing temperature, thermal activation induces space charge and domain dynamics, causing Maxwell–Wagner polarization and polarization switching in the ceramic at lower electric fields. As benefited from the Sb-doping effect and an optimized MPB, the sample with x = 0.47 obtained excellent mechanical and electrical properties including H_v=3.97 GPa, d₃₃=529 pC/N, T_C=277 °C, ε_r=1167, P_r=28.33 μC/cm², and FOM (d₃₃×g₃₃)=27.08×10⁻¹² m²/N, which provide this material with enormous competitiveness for applications in piezoelectric energy harvesters.