Achieving high electromechanical response in lead-free BNT-BT ceramics through synergistic A/B-site doping

Lead-free Bi_0.5Na_0.5TiO₃-based ceramics show great promise for achieving high unipolar strain. However, it remains challenging to implement an effective strategy for microstructural designs with high electromechanical response. Herein, a direct composition-engineering method based on A/B-sites doping is adopted to introduce a synergistic effect of reduced oxygen vacancies, lattice distortion, ferroelectric-to-relaxor phase transition, and nano-sized domains, resulting in a high piezoelectric strain coefficient d^*₃₃ of 857 pm/V at a small electric field of 4 kV/mm. Furthermore, a large room-temperature maximum polarization (P_m) of 72.4 μC/cm² was observed at high electric field. A phase transition from coexisting rhombohedral-tetragonal to pseudocubic was engineered by finely tuning the contents of NaTaO₃, leading to a decrease in both remnant polarization (P_r) and coercive field (E_c). The phase diagram of 1-x[0.935(Bi_0.5Na_0.5TiO₃)-0.065(BaTi_0.99Nb_0.01O₃)]-x(NaTaO₃) (x = 0-0.04) is proposed, providing a roadmap for engineering high-performance piezoelectric ceramics with enhanced electrostrain responses, which may find potential applications as piezoelectric actuators.