The mechanism for the enhanced piezoelectricity, dielectric property and thermal stability in (K,Na)NbO3 ceramics

In the context of piezoelectric applications, it is essential not only to achieve a high piezoelectric coefficient but also to ensure excellent overall performance, which includes appropriate dielectric property and superior thermal stability. Despite two decades of research, (K,Na)NbO₃ (KNN) ceramics have been recognized as a lead-free ferroelectric material capable of replacing PZT ceramics, the relationships between structure, piezoelectricity, dielectric property, and thermal stability remain incompletely understood. Here, taking piezoelectric energy harvester (PEH) as an example, we combined property measurements and atom-scale scanning transmission electron microscopy (STEM) and phase-field simulations to establish the structure-property relationship in lead-free KNN ceramic. The results indicate that the energy harvesting performance of KNN reaches its peak when polarization configuration achieves a balance between the enhancement of piezoelectric coefficient and dielectric permittivity. Large angle polarization at the scale of ∼5–10unit cells embedded within the long-range order T phase can lead to high piezoelectric coefficient, moderate dielectric permittivity, superior temperature stability, and excellent energy harvesting performance. This work elucidates the relationship between structure and properties in KNN piezoceramic and provides guidance for the design of high-performance ferroelectric ceramic for PEH, which is expected to benefit the design of lead-free piezoceramics for other piezoelectric applications.