Competing lead-driven defect regulating mechanisms and their impact on polarization and piezoelectricity in ferroelectric perovskite ceramics

Lead-based ferroelectric ceramics are promising materials for high-temperature piezoelectric applications. However, their thermal stability is often limited by lead volatility and defect-induced conduction. This work elucidates the effect of excess PbO on the evolution of defects and polarization behavior of BiFeO₃-PbTiO₃-Ba(Zr,Ti)O₃ ceramics. By employing detailed experimental characterization and first-principles calculations, we demonstrate that minor fluctuations in the level of excess lead induces significant variations in the crystal and defect structures. These variations are shown to subsequently trigger a shift in the rhombohedral-tetragonal-pseudocubic (R - T - P c) phase boundary and a relaxor ferroelectric phase transition from the ergodic to nonergodic state. The presence of a moderate level of excess PbO is shown to suppress the formation of lead and oxygen vacancies, thereby enhancing ferroelectric stability, whereas the incorporation of an excessive level of Pb promotes Pb⁴⁺ formation and lattice distortion. This system simultaneously achieves an enhanced piezoelectric response (d ₃₃ ∼ 260 pC/N) and temperature stability, with a d ₃₃ variation of less than 8% from room temperature to 218.6°C. This work therefore provides new insights into defect regulation mechanisms, providing theoretical guidance for the design of lead-based perovskite ceramics with superior high-temperature piezoelectric properties.