Bi_0.48(Na_0.84K_0.16)_0.48Sr_0.04(Ti_1-xTa_x)O₃ lead-free ceramics with enhanced electric field-induced strain

A series of Bi_0.48(Na_0.84K_0.16)_0.48Sr_0.04(Ti_1-xTa_x)O₃ (abbreviated as NKS-100xTa) lead-free piezoelectric ceramics were fabricated using a traditional solid-state method. The structure and electrical properties of NKS-100xTa were investigated in detail. The composition for x = 0.01 presented an enhanced electric field induced bipolar strain of ∼0.53%, as well as the giant unipolar strain of ∼0.478% corresponding to S_max/E_max ∼682 p.m./V at 70 kV/cm. It is found that the ferroelectric-relaxor transition temperature (T_F-R) shifted down to ambient temperature and the remnant polarization (P_r) decreased with the Ta doping. It destroyed the long-range ferroelectric ordering and increased the relaxor characteristic. Therefore, the origin of giant strain was ascribed to the transformation from the ferroelectric phase to relaxor phase under the applied electric field. In addition, the well fatigue properties within 10⁴ cycles indicated that the prepared ceramics offered extendable availability for sensors and actuators.