High-performance lead-free piezoelectrics with local structural heterogeneity

The temperature sensitivity of enhanced piezoelectricity in (K,Na)NbO ₃ perovskite-based lead-free piezoelectrics is one of the technical bottlenecks impeding practical applications. This work found a recipe that possesses a piezoelectric strain coefficient d ₃₃ ∗ as high as 600 pm V ^-1 over a wide temperature range up to 100 °C, which is additionally insensitive against the frequency of an applied electrical field. Electrical property measurement and nanostructure observation revealed that the high performance combining high piezoelectricity and excellent stability benefits from a diffused phase transition (DPT), which is closely associated with the transition from ferroelectric to relaxor behavior induced by the local structural disorder due to the complicated compositional modification. The high-resolution transmission electron microscopy images of Moiré fringes imply the existence of polar nanoregions (PNRs) that are responsible for the relaxor-like electrical behavior in the present materials. The findings and understanding obtained in this work should be valuable for pushing lead-free piezoelectric ceramics towards practical applications.