Achieving well-balanced performance of d33 and Td in unmodified morphotropic phase boundary BNKT20 ceramics by optimizing phase structure

The incompatibility of the large piezoelectric response ( d 33 ) and high depolarization temperature ( T d ) in lead-free piezoelectric ceramics limited their practical applications. The most used modification methods for improving d 33 or T d commonly required a delicate control of complex compositions. Here, a strategy for simply changing the sintering temperature is used to defer the T d and increase d 33 simultaneously. The T d and d 33 of unmodified Bi 0.5 Na 0.5 TiO 3 -0.2Bi 0.5 K 0.5 TiO 3 (BNKT20) ceramics increase with increasing sintering temperature until both of them reach the maximum ( d 33  ~ 174pC/N, T d  ~ 177 °C) at the sintering temperature of 1100 °C. In-depth analysis unveils the critical role of multiphase coexistence and oxygen vacancies in enhancing T d by optimizing sintering temperature. Meanwhile, increasing sintering temperature promotes large grain size with easy domain orientation, thus, yielding the improved d 33 . This work provides a simple and effective method to broaden the working range of Bi 0.5 Na 0.5 TiO 3 -based (BNT) piezoelectric ceramics at high temperature under the premise of realizing high piezoelectric properties.