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

Abstract 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.