Pivotal role of polarization coupling on strain evolution in BNT-based systems

Bismuth sodium titanate [Bi _0.5Na _0.5TiO ₃ (BNT)]-based relaxors exhibit outstanding strain performances, making them valuable for piezoelectric actuators. Although various giant strain BNT-based systems have been constructed, the chemical modification on BNT ceramics still require amounts of trial-and-error experiments. Herein, based on the typical ferroelectric/relaxor theory and Preisach model, we propose new insight into the strain regulation mechanism to simplify the design of giant strain BNT-based systems. The polarization coupling effect, a kind of structure-driven interatomic interaction, is observed in BNT-based systems, which dominates the strain evolution process. Hence, tailoring the polarization interaction can effectively modify the macroscopic strain performances, including both the strain value and reversibility. Under specific condition, where the ergodic polar units combining with long-range polar structures in well-balanced proportions, the polarization coupling effect can induce the formation of a metastable ferroelectric state. This leads to the accelerated phase transition process while preserving reversibility, which is further validated in critical (Bi _0.5Na _0.36K _0.1Li _0.04) _0.995Sr _0.005Ti _0.95Ta _0.05O ₃ and (Bi _0.5Na _0.4K _0.1) _0.99Sr _0.01Ti _0.99Ta _0.01O ₃ (KLST-T and KST-T, respectively) systems within this work. Overall, these findings provide potential avenues for precise control and manipulation of the functionalities in BNT-based relaxors.