Aliovalent co-doping induces relaxor states with enhanced electrostrain in BNT-based ceramics

Developing high-performance lead-free electrostrain materials is key to advancing next-generation electromechanical technologies. Here we report an aliovalent co-doping strategy in (Bi_0.5Na_0.5)TiO₃-based (BNT-based) ceramics, where simultaneous A-site (Li⁺) and B-site (Nb⁵⁺) co-doping yields (1−x)Bi_0.5(Na_0.81K_0.19)_0.5TiO₃-xLiNbO₃ (BNKT-xLN, x = 0.01–0.04) compositions. The aliovalent substitution disrupts long-range ferroelectric order, enhances lattice distortion, and promotes a relaxor-like state with diffuse phase transitions and strong dielectric dispersion. Complementary polarization–electric field (P–E) and strain–electric field (S–E) measurements demonstrate a progressive evolution from classical ferroelectrisc to nonergodic relaxor behavior as the doping level increases. The optimized composition at x = 0.02 exhibits a large reversible electrostrain of approximately 0.55% associated with a temperature-driven reversible phase transition. Notably, BNKT-xLN ceramics achieve electric-field-induced polarizations exceeding 50 μC/cm², while exhibiting a relatively low electrostrictive coefficient Q₃₃ of ∼0.018 m⁴/C², suggesting their potential as energy storage matrices due to the weak polarization–strain coupling effect. These results underscore the importance of aliovalent co-doping strategy in modulating the energy landscape of BNT-based systems, offering a viable strategy for developing high-strain, lead-free electroceramics suited to next-generation actuators and energy storage devices.