Defect-engineered strain enhancement via phase redistribution and electrostrictive coupling in predominantly ergodic BNT-based ceramics

Electrostrain in lead-free relaxor piezoceramics is governed by the interplay between phase heterogeneity and defect-mediated polarization dynamics. Here, a BNT-SBT ceramic system is employed to elucidate how thermal post-processing modulates electromechanical behavior without compositional modification or external conditioning. The treatment induces a redistribution of rhombohedral (R3c) and tetragonal (P4bm) phase fractions, accompanied by reconfiguration of defect-related environments. Electron paramagnetic resonance reveals the presence of oxygen-vacancy−related defect states, while XPS analysis indicates a redistribution of near-surface oxygen chemical states. Despite the mixed-phase structure, polarization measurements exhibit diffuse relaxor characteristics, suggesting that long-range domain switching plays a limited role, whereas the reversible strain response is predominantly governed by electrostrictive polarization dynamics, facilitated by oxygen-vacancy–related defect states. A significant enhancement in electrostrictive response is confirmed by the increased electrostrictive coefficient (Q₃₃) and the linear S–P² relationship. Consequently, the maximum strain increases from 0.25% to 0.51%, with a normalized strain coefficient of 729 pm⋅V⁻¹. The results indicate that the enhanced strain originates from an electrostriction-dominated response enabled by processing-induced defect-phase coupling and local structural heterogeneity. This work provides a processing-driven pathway for tuning electromechanical properties in BNT-based relaxor ceramics and offers insight into strain generation mechanisms beyond conventional domain-switching models.