Realizing an Ultrahigh Depolarization Temperature near the Curie Point and Large d₃₃ with Superior Temperature...

An imminent challenge of lead-free Bi_0.5Na_0.5TiO₃-based (BNT) piezoceramics is that the giant piezoelectric constant (d₃₃) caused by the morphotropic phase boundary is incompatible with a high depolarization temperature (T_d) and ultralow temperature coefficient (T_tc) of the real-time d₃₃, which severely hinders their industrial application in the field of elevated temperatures. Herein, a sandwich-structured 0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃/0.89Bi_0.5Na_0.5TiO₃-0.11BaTiO₃/0.94Bi_0.5Na_0.5TiO₃-0.06BaTiO₃ (SWS-6/11/6BT-y, where y refers to the weight fraction of the BNT-11BT solid solution) ceramic composite is engineered for mitigating the conflict between d₃₃, T_d and T_tc. Following this strategy, ultrahigh T_d near the Curie point (225 °C, close to that of the BNT-11BT layer) and relatively large d₃₃ (130 pC/N, close to that of the BNT-6BT layer) are simultaneously realized in a SWS-6/11/6BT-40%-Q ceramic composite. More importantly, the ultralow T_tc (0.07%) of real-time d₃₃ is also achieved in this work. The structural heterogeneity yields the high piezoresponse, and the built-in field resulting from layer-type ceramic composites provides the driving force to promote the diffused ferroelectric-relaxor phase transition and the resultant ferroelectric order with high T_d. The above synergistic contributions realize the remission of the d₃₃-T_d-T_tc conflict in a sandwich-structural SWS-6/11/6BT-40% ceramic composite. Thus, our work provided a path for designing the BNT-based piezoceramics with potential for industrial applications.