Relationship between Poling Characteristics and Phase Boundaries of Potassium–Sodium Niobate Ceramics

The controversy about the optimum poling conditions of (K,Na)NbO3 (KNN)-based lead-free ceramics was still unresolved and the relationships between poling characteristics and phase boundary types were rarely mentioned. Here, we tried to unveil the relationships between poling characteristics and phase boundary types of these ceramics. The optimum poling temperatures should be chosen near their corresponding phase transition temperatures. In addition, a large piezoelectricity can be attained in the ceramics with a multiphase coexistence under a lower poling electric field (<E(C)), while a higher poling electric field (≥E(C)) is required to achieve the sufficient polarization in the ones with single O or T phase. More interestingly, it is the first time to report that the ceramics with different phase boundaries can be fully poled after the measurement of P-E loops, where the d33 values match those of the corresponding ones poled by the DC electric field. We believe that this modified poling process can benefit the improved piezoelectricity of KNN-based ceramics.