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)NbO3 (KNN) lead-free ceramics to maintain relatively stable electrical properties. The raw material Bi2O3 is more sensitive to high temperature. To improve electrical properties, it is more necessary to compensate the volatile Bi. In this work, the 0.96K0.48Na0.52Nb0.96Sb0.04O3-0.04Bi0.5*(1+x)Na0.5ZrO3 (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 (d33 = 522 pC/N, kp = 58.9%, Tc = 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.