Synergy of morphotropic phase boundary and internal bias fields to achieve high d33 and d33* simultaneously in lead-free BNT-based ceramics

It is difficult to obtain high d33 and d33* simultaneously in one piezoelectric ceramic system via a conventional method due to the conflicting structure–properties responding mechanism between the direct piezoelectric and converse piezoelectric effects. In this work, a synergistic approach of constructing morphotropic phase boundary and introducing the internal bias fields in (Bi0.5Na0.5)TiO3 ceramics is proposed through Sr2+ and Li+ doping for mitigating the conflict between d33 and d33*. By this strategy, both high d33 (197 pC/N) and d33* (1500 p.m./V) are realized in Srx(Bi1-xNa0.97-xLi0.03)0.5TiO3 when x = 0.24. The large d33 stems from rhombohedral and tetragonal (R3c and P4bm) phase coexistence. The internal bias field introduced by defect dipoles tends to counteract the effects of depolarization field, thus greatly aiding the external fields with higher actual excitation fields. The superposition of internal bias field, depolarization field and external fields yields strong asymmetry bipolar strain curves, thereby contributing to the large d33*. Thus, this work opens a new door for developing lead-free ceramics with excellent piezoelectric performance.