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 0.5 Na 0.5 )TiO 3 -based (BNT-based) ceramics, where simultaneous A-site (Li + ) and B-site (Nb 5+ ) co-doping yields (1− x )Bi 0.5 (Na 0.81 K 0.19 ) 0.5 TiO 3 - x LiNbO 3 (BNKT- x LN, 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- x LN ceramics achieve electric-field-induced polarizations exceeding 50 μC/cm 2 , while exhibiting a relatively low electrostrictive coefficient Q 33 of ∼0.018 m 4 /C 2 , 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. • Aliovalent co-doping enhances electrostrain in BNT-based ceramics • Relaxor behavior induced by Li/Nb dopants stabilizes polar nanoregions • BNKT-0.02LN exhibits large reversible electrostrain of ∼0.55% • Weak polarization–strain coupling indicates energy storage potential • Site engineering reshapes energy landscape for lead-free electromechanical use