Enhanced Piezoelectric\nResponse Attained by Defect\nDipoles in BiFeO<sub>3</sub>‑based Lead-Free Ceramics

The impact of defects on the performance of piezoelectric\nmaterials\nhas been a topic of considerable debate, due to the competing actions\nof the deteriorating effect of the defects themselves on the ceramic\nresistance and the positive effect on the piezoelectric performance\nresulting from the defect polarization. In order to probe its combined\ninfluence on piezoelectric properties, here, we designed BiFeO<sub>3</sub> (BF)-based ceramics with different defect concentrations.\nIt has been demonstrated that the incorporation of an appropriate\nconcentration of defects into ceramics can effectively enhance their\npiezoelectric properties while maintaining their insulating properties.\nDuring the polarization process, both the intrinsic polarization and\ndefect dipoles are oriented along the direction of the electric field.\nThis occurs in the presence of a high temperature environment as well\nas an applied electric field, which results in a complementary enhancement\nof the macroscopic ferro- and piezoelectric properties. Consequently,\nthe piezoelectric performance of BF–BT–BKT ceramics\nis achieved (<i>d</i><sub>33</sub> = 203 ± 5 pC/N, <i>T</i><sub>C</sub> = 502 °C, <i>k</i><sub>p</sub> = 33.05%). This work provides a framework for understanding the\nintrinsic structural mechanism of bismuth ferrate.