Realizing an Ultrahigh Depolarization Temperature near the Curie Point and Large d 33 with Superior Temperature Stability in Lead-Free Ceramics via a Sandwich Structure Design.

An imminent challenge of lead-free Bi 0.5 Na 0.5 TiO 3 -based (BNT) piezoceramics is that the giant piezoelectric constant ( d 33 ) 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 d 33 , which severely hinders their industrial application in the field of elevated temperatures. Herein, a sandwich-structured 0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 /0.89Bi 0.5 Na 0.5 TiO 3 -0.11BaTiO 3 /0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3 (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 d 33 , 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 d 33 (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 d 33 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 d 33 - 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.