High‐Performance Lead‐Free Ceramics With Simultaneously High Piezoelectricity and High Mechanical Quality Factor

Piezoelectric materials with a high piezoelectric coefficient (d₃₃) and high mechanical quality factor (Q_m) are vital for advanced high-power applications. However, achieving this combination is challenging, particularly for lead-free piezoelectrics, because a high d₃₃ value relies on mobile domain walls, which increase dissipative losses and reduce Q_m. In this study, this longstanding trade-off is overcome by introducing defect dipoles (via Mn doping) into the quadruple point (QP) composition of the lead-free Ba(Sn, Ti)O₃ system. The resultant 0.5%Mn-doped Ba(Sn_0.11Ti_0.89)O₃ (BST-0.5%Mn) ceramic exhibits a high d₃₃ value of 710 pC/N and high Q_m value of 929, while the BST-1%Mn ceramic achieves a d₃₃ value of 614 pC/N and Q_m value of 1138. These values represent a 10-fold increase in Q_m and 1.6-fold increase in d₃₃ for BST-0.5%Mn, compared to those for undoped BST. High-resolution scanning transmission electron microscopy and phase-field simulations reveal that the enhanced d₃₃ and Q_m are attributable to the coexistence of multiple phases of QPs with symmetry-conforming defect dipoles, challenging the long-held notion of physical incompatibility between high d₃₃ and high Q_m. These findings offer a pathway for designing eco-friendly piezoelectric materials with unprecedented performance, paving the way for sustainable and efficient high-power applications.