Ultralow Dielectric Loss with Excellent Thermal Stability in BiScO₃-PbTiO₃ Piezoelectric Ceramics via Phase Structure...

BiScO₃-PbTiO₃ (BS-PT) ceramics combine high piezoelectricity and a high Curie temperature but are limited in power applications by high dielectric loss (tan δ ≈ 4%) and low mechanical quality factor (Q_m ≈ 28). Here, we introduce relaxor ferroelectric Bi(Mn_2/3Nb_1/3)O₃ (BMN) to construct a T-rich morphotropic phase boundary (MPB), achieving simultaneous reduction of tan δ and enhancement of Q_m without significant degradation of piezoelectric properties. The optimized 0.02BMN-BS-0.635PT composition delivers tan δ = 0.57%, d₃₃ = 365 pC/N, Q_m = 124, k_p = 0.53, k_t = 0.54, and T_c = 435 °C. Mn-substitution at the B-site generates oxygen vacancies that couple with receptor centers to form defective dipoles, and their strong interaction with the T-rich phase suppresses polarization rotation and domain-wall motion, yielding reduced dielectric loss and enhanced Q_m, while relaxor-induced polar nanodomains help maintain a high d₃₃ value. In situ electrical and structural characterizations demonstrate excellent thermal stability: k_p and k_t remain 0.5 at 300 °C with <7% variation, and d₃₃ increases continuously up to 300 °C, indicating a depolarization temperature above this threshold. High-temperature XRD further shows that the rhombohedral-to-tetragonal phase ratio is stable below 300 °C, consistent with the T-rich MPB design at room temperature, accounting for the observed robustness. This study demonstrates the potential of BMN-BS-PT ceramics for high-temperature, high-power piezoelectric applications and establishes a generalizable phase structure regulation strategy for designing advanced piezoelectric ceramics.