Superior electrostrain with excellent thermal stability by constructing glassy ferroelectric crossover

Simultaneous enhancement in both strain response and thermal stability has been a longstanding challenge in lead-free ferroelectrics due to the failure in stabilizing the microstructure features of large electrostrain over a wide temperature range, viewed as a considerable limitation for practical utility. In this work, a promising electrostrain of approximately 0.4 % with a fluctuation of <5 % within the temperature range of 300–380 K is attained in the Ta-modified (Bi, Na)TiO₃-BaTiO₃ ceramics through constructing a glassy ferroelectric crossover near the composition displaying the field-induced transitions from relaxor to coexistent rhombohedral+tetragonal ferroelectric phases of MPB (relaxor→MPB). It exceeds the electrostrain performance of neighboring compositions unilaterally displaying relaxor→MPB transition or pure glassy behavior when taking both electrostrain amplitude and thermal stability into consideration. Phase field simulation indicates that the combination of enhanced electrostrain and excellent thermal stability is ascribed to the embedding the nano-scaled glassy ferroelectric state within the MPB region of the relaxor→MPB composition, a feature enabled through introducing local fields by Ta-doping process. The optimal coexistence of micro and nano domain patterns in designed glassy ferroelectric crossover smears the microstructural difference between relaxor and MPB ferroelectric regions. It allows the easy and recoverable domain wall motion across a wide temperature range, resulting in the favorable electrostrain output with excellent thermal stability. This research proposes a novel strategy for improving thermal-stable electrostrain amplitude in eco-friendly ferroelectrics, thereby facilitating the advancement of lead-free piezoelectric technologies.