Ultralow Dielectric Loss with Excellent Thermal Stability in BiScO 3 –PbTiO 3 Piezoelectric Ceramics via Phase Structure Regulation

BiScO 3 –PbTiO 3 (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 2/3 Nb 1/3 )O 3 (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%, d 33 = 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 d 33 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 d 33 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.