Improvement of electrostrain properties of BNT-based piezoelectric ceramics by co-doping of Sr2+ and Ta5+ in A and B sites

Lead-free piezoelectric ceramics of the [0.852(Bi 0.5-x Sr x Na 0.5 )-0.11(Bi 0.5 K 0.5 )-0.038Ba]Ti (1-x) Ta x O 3 (designated as BNKT-BT-xTaSr) ternary system were prepared with co-doping of Ta 5+ and Sr 2+ . The purpose of this study is to investigate the effects of co-doping of Ta and Sr element on the microstructure, phase structure electrical properties, and electrostrain behavior of BNKT-BT-xTaSr ceramics. With the increase of Ta 5+ and Sr 2+ doping, the transition temperature ( T F-R ) of the modified doped BNKT-BT-xTaSr ceramics from ferroelectric to relaxed phase decreases to below room temperature (RT). When x = 0.005, the BNKT-BT-xTaSr ceramics reached a large electrostrain of 0.46%( d * 33  = 657 p.m./V) at RT under an electric field of 7 kV/mm, which is caused by the transition from ergodic relaxor phase to ferroelectric phase under a high applied electrical field. In addition, the electrostrain is increased to 0.48% ( d * 33  = 685 p.m./V) under the same electric field after the thermal aging process at 80 °C for two weeks. This study demonstrates that the A/B site co-doping could effectively improve the electrostrain properties of BNKT-BT-xTaSr ferroelectric ceramics .