Correlation between phase, microstructure and electrical properties of KNN-modified BNT-BT lead free ceramics

To enhance the piezoelectric performance of the lead-free Bi 0.5 Na 0.5 TiO 3 -BaTiO 3 (BNT-BT) system, we introduced K 0.5 Na 0.5 NbO 3 (KNN) via synergistic composition modulation. A series of (0.94-x)BNT-0.06BT-xKNN (x = 0.01–0.04) ceramics were synthesized using a solid-state reaction method. The composition with x = 0.02 exhibited optimal performance, achieving a significantly improved piezoelectric coefficient ( d ₃₃ = 115 pC/N) and a high depolarization temperature ( T d = 138 °C). Comprehensive structural and electrical characterizations revealed that these enhancements originate from KNN-induced modifications, including the coexistence of rhombohedral and tetragonal phases, refined grain morphology, and optimized domain dynamics. This work demonstrates that KNN modification is an effective strategy for tailoring the functional properties of BNT-BT-based ceramics, positioning the optimized composition as a competitive lead-free piezoelectric candidate for advanced electromechanical applications.