Enhanced Electrical and Thermal Stability in (K,Na)NbO₃ Ceramics via Compositional Engineering

Lead-free (K,Na)NbO3 (KNN)-based piezoceramics are being pursued for the next generation of actuators. The piezoelectric properties of KNN can be improved by synthesizing a multiphase composition with an optimal microstructure. However, in conjunction with an ultrahigh piezoelectric coefficient (d33), the stability of piezoelectric properties under a high external electric field and temperature is crucial. Here, we demonstrate a multiphase (1 – y)(K0.48Na0.52)(Nb0.96Sb0.04)O3-yAgx(Bi0.5Na0.5)(1–x)ZrO3 (KNN-Ag-BNZ) composition exhibiting increased electromechanical properties with enhanced electrical and thermal stability. The composition with x = 0.1 and y = 0.05 merges the ferroelectric rhombohedral-orthorhombic-tetragonal phases, resulting in high d33 ∼ 570–600 pC/N and d*33 ∼ 600 pC/N (at 10 kV/mm) at room temperature. Electromechanical coupling factors (kp and k31) exhibited a stable magnitude up to the Curie temperature (205 °C). The performance of KNN-Ag-BNZ was evaluated under a high drive field (45–55% Ec) by measuring piezoelectric displacement and dielectric loss (tan(δ)), and the results were compared with commercial PZT 8. This composition also exhibited high fatigue resistance at an electric field up to 104 cycles. Overall, the results demonstrate an excellent combination of high electromechanical properties with good thermal stability and high voltage tolerance, making it a promising candidate for actuation applications.