Exploiting the Competition Between Antiferroelectric and Ferroelectric Orders for Ultrahigh Electromechanical Response

High electromechanical responses are typically found in materials with strong structural instabilities, typically achieved through two common approaches: morphotropic phase boundaries and nanoscale structural heterogeneity. In this study, we present an alternative strategy for achieving ultrahigh electromechanical responses by inducing extreme structural instability through the competition between antiferroelectric and ferroelectric orders. Guided by the phase diagram and theoretical calculations, we designed sodium niobate thin films to simultaneously exhibit antiferroelectric orthorhombic and ferroelectric rhombohedral phases. These films demonstrate effective piezoelectric coefficients exceeding 5000 picometers per volt driven by electric field-induced transitions between the antiferroelectric and ferroelectric phases. Our findings offer a novel method to design and optimize antiferroelectric materials for advanced electromechanical applications.