Practical high strain with superior temperature stability in lead-free piezoceramics through domain engineering

An easy-to-use domain strategy by utilizing phase boundary design, chemical modification, and electric-field driving was employed to optimize strain and temperature stability of a polycrystalline ceramic. First, the effects of phase boundary, composition, and electric field on the domain were investigated in detail. Distinct spontaneous polarization rotation appears in various phase transition processes, inducing different evolution of domain structure and piezoresponse at elevated temperatures. Measurements reveal that the domain at the rhombohedral-tetragonal (R-T) phase boundary shows giant piezoresponse and high temperature stability. The structure origin is assigned to the slow degradation of spontaneous polarization, and the highly steady domain contribution stimulates excellent strain stability at the R-T phase boundary. Additionally, doped components significantly influenced domain stability, and boosted electric fields stabilized the piezoresponse of the domain. Second, modulating domain stability and its piezoresponse through tuning the phase boundary and driving field, as well as chemical modification, realized a large and temperature-insensitive strain fluctuation less than 3% at 23-80 degrees C) in (K, Na)NbO3 (KNN)-based ceramics. This value is largely superior to that obtained from current lead-free piezoelectric materials and some soft lead-based counterparts, indicating a tremendous application potential for (K, Na)NbO3 (KNN)-based ceramics. This study affords a significant guidance for designing lead-free piezoelectric materials with high piezoelectricity and temperature stability.