Significantly enhanced mechanical quality factor of acceptor-doped quadruple point composition in lead-free Ba(Zr,Ti)O₃ ceramics

High mechanical quality factor (Q_m) is crucial in high-power applications of piezoelectric ceramics because it affects key performance parameters such as sensitivity, efficiency, and stability of devices. Acceptor doping has been the state-of-the-art approach to improve Q_m. In the past few decades, many previous research has focused on acceptor doping at the phase boundary to achieve high-performance piezoelectric ceramics. Here, we found that compared with the acceptor-doped phase boundary compositions, the acceptor-doped quadruple point composition can achieve significantly enhanced Q_m. The optimal Q_m value is up to 1100, which is three times higher than the Q_m (approximately 254) obtained in the acceptor-doped phase boundary composition, and also higher than the Q_m obtained in the acceptor-doped single-phase region compositions. Piezoresponse force microscopy (PFM) characterization reveals that the pinning effect induced by defect dipoles is more pronounced in the acceptor-doped quadruple point composition compared with the acceptor-doped phase boundary composition, resulting in reduced domain mobility and enhanced Q_m. This work provides new insights into the design of lead-free and lead-based piezoelectric materials with high mechanical quality factors.