Giant strain response in 2 mol% Nb-doped (Bi_0.5Na_0.4K_0.1)TiO₃ lead-free ceramics

A series of Nb-doped (Bi_0.5Na_0.4K_0.1)TiO₃ lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method. The X-ray diffraction patterns reveal a pure perovskite structure for all the samples. A giant strain of 0.34% is achieved at 2 mol% Nb-doping concentration, and the corresponding normalized strain d33∗ reaches 625 pm V⁻¹, which is one of the best results of the BNT-based ceramics. Complex ac impedance data indicate that only the bulk effect contributes to the resistivity. The compositionally induced disruption of long-range ferroelectric order and relaxor transition contributed to the pinched polarization loops as well as the large electric field-induced strain. The results indicate that appropriate Nb-dopant content can remarkably enhance the strain level of (Bi_0.5Na_0.4K_0.1)TiO₃ ceramics, making it a promising candidate for actuator applications.