Synergistic Phase Boundary and Defect Engineering Enables Ultrahigh Electrostrain in Lead-Free Ceramics

Piezoelectric ceramics serve as essential materials for electromechanical transduction; however, they face two critical limitations: the environmental toxicity associated with conventional lead-based systems and the inadequate strain performance, typically below 0.5%, observes in current lead-free alternatives. In this work, a synergistic design approach is presented to address both challenges by simultaneously modulating the room-temperature nonergodic relaxor to ergodic relaxor phase boundary and introducing engineered defect dipoles (P_d) in (Bi_0.5Na_0.5)_0.93Ba_0.07TiO₃ (BNBT) ceramics through B-site co-substitution with aliovalent (Sn_0.5Sb_0.4)⁴⁺ complex ions. This dual-modulation strategy leverages field-induced phase transitions, the morphotropic phase boundary effect, and the cooperative alignment between spontaneous polarization and defect dipole polarization. As a result, the material system exhibits markedly suppressed negative strain, a substantial internal bias field that facilitates reversible domain switching, and an exceptional electromechanical response. Specifically, an ultrahigh electrostrain of 1.06%, a giant effective piezoelectric coefficient of 1317 pm V⁻¹, and an ultralow strain hysteresis of 7.2% are achieved. These metrics rival those of benchmark lead-based ceramics such as Pb(Zr_1-xTi_x)O₃. The proposed methodology offers a promising pathway for the development of high-performance, environmentally benign actuator materials suitable for advanced electromechanical applications.