Enhanced electromechanical response in (K, Na)NbO3-based ferroelectrics by phase boundary and nonstoichiometry engineering

Compositional fluctuation of the K and Na elements during the preparation process becomes a major issue for (K,Na)NbO 3 (KNN) lead-free ceramics to maintain relatively stable electrical properties. The raw material Bi 2 O 3 is more sensitive to high temperature. To improve electrical properties, it is more necessary to compensate the volatile Bi. In this work, the 0.96K 0.48 Na 0.52 Nb 0.96 Sb 0.04 O 3 -0.04Bi 0.5*(1+ x ) Na 0.5 ZrO 3 ( x  = −0.05, −0.02, 0.00, 0.02, 0.05, and 0.08) ceramics were selected as basis material. The excess Bi can increase the phase fraction of the T phase and decrease oxygen vacancy content, which effectively enhance the extrinsic contribution of the piezoelectric response. The electromechanical properties were optimized by excess Bi, and the optimal properties ( d 33  = 522 pC/N, k p  = 58.9%, T c  = 235 °C) were obtained in the ceramic with x  = 0.05. The present work provides new guidelines for enhancing the piezoelectric performance of KNN ceramics by a simple method, which can be applied to other lead-free piezoelectric ceramic systems.