Electrostrain performance and the relaxor state on polarization scaling behaviors of sodium bismuth titanate-based ferroelectrics

Bismuth sodium titanate (BNT)-based ceramics have attracted extensive attention due to their potential as lead-free piezoelectric materials. In this work, doping KNbO₃into BNT-based ceramics effectively induces a transition from a non-ergodic relaxor (NR) state to an ergodic relaxor (ER) ferroelectric state. This work systematically elucidates the correlation among relaxation properties, electrostrain properties, and scaling behaviors. The ER ferroelectrics show dispersive polarization with persistent non-180° domain switching and polar nanoregions (PNRs) reorganization over broad electric fields, leading to continuously increasing strain under high fields. Frequency-dependent measurements reveal that freezing frequency decreases with increasing AC field amplitude, and the freezing frequency is closely related to internal bias field transition frequency. ER systems show positive frequency scaling exponent (α) indices under low frequencies and low electric fields due to rapid reversibility of polar nano regions, while NR materials show negative α indices. This work provides a novel theoretical paradigm for lead-free piezoelectric design and aids in understanding the dynamic ferroelectric hysteresis.