Enhanced Piezoelectric Response Attained by Defect Dipoles in BiFeO₃-based Lead-Free Ceramics

The impact of defects on the performance of piezoelectric materials has been a topic of considerable debate, due to the competing actions of the deteriorating effect of the defects themselves on the ceramic resistance and the positive effect on the piezoelectric performance resulting from the defect polarization. In order to probe its combined influence on piezoelectric properties, here, we designed BiFeO₃ (BF)-based ceramics with different defect concentrations. It has been demonstrated that the incorporation of an appropriate concentration of defects into ceramics can effectively enhance their piezoelectric properties while maintaining their insulating properties. During the polarization process, both the intrinsic polarization and defect dipoles are oriented along the direction of the electric field. This occurs in the presence of a high temperature environment as well as an applied electric field, which results in a complementary enhancement of the macroscopic ferro- and piezoelectric properties. Consequently, the piezoelectric performance of BF-BT-BKT ceramics is achieved (d₃₃ = 203 ± 5 pC/N, T_C = 502 °C, k_p = 33.05%). This work provides a framework for understanding the intrinsic structural mechanism of bismuth ferrate.