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 0.5 Na 0.5 ) 0.93 Ba 0.07 TiO 3 (BNBT) ceramics through B‐site co‐substitution with aliovalent (Sn 0.5 Sb 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‐ x Ti x )O 3 . The proposed methodology offers a promising pathway for the development of high‐performance, environmentally benign actuator materials suitable for advanced electromechanical applications.