Large Electrostrain Induced by Co-Doping of Sr2+ and Ta5+ in a and B Sites for Bnt-Based Piezoelectric Ceramics

Abstract

Lead-free piezoelectric ceramics of the [0.852(Bi0.5Na0.5)-0.11(Bi0.5K0.5)-0.038Ba]TiO3 (designated as BNKT-BT) ternary system   were co-doped with Ta5+ and Sr2+. The purpose of this study is to investigate the effects of Ta/Sr element co-doping on the phase structure, microstructure, electrical properties, and electrostrain behavior of BNKT-BT ceramics. With increasing doping content, the transition temperature of ferroelectric phase to relaxor state (TF-R) drops to below room temperature, and the BNKT-BT ceramics co-doped with Ta5+ and Sr2+ exhibit the characteristics of relaxor at room temperature. When x = 0.005, a large electrostrain of 0.46% (d*33 = 657 pm/V) is obtained under the 7 kV/mm, suggesting that the large electrostrain resulted from the transition of ergodic relaxor to the ferroelectric phase under the high applied electrical field. In addition, the electrostrain is increased to 0.48% (d*33 = 685 pm/V) under the same electric field. after the aging process (for two weeks at 80°C). This study demonstrates that the A/B site co-doping could effectively improve the electrostrain properties of BNKT-BT ferroelectric ceramics.

Keywords: Phase transition, A/B site co-doping, electrostrain, aging