This study demonstrates a novel approach to achieve ultrahigh electromechanical response in materials by inducing extreme structural instability through the competition between antiferroelectric (AFE) and ferroelectric (FE) orders. The researchers designed sodium niobate (NaNbO₃, NNO) thin films to coexist both AFE and FE phases, guided by the phase diagram and theoretical calculations. These films exhibit effective piezoelectric coefficients exceeding 5,000 pm V⁻¹ due to electric-field-induced phase transitions from AFE to FE. The results provide a general strategy for designing and exploiting antiferroelectric materials for electromechanical devices, offering significant advancements in the field of piezoelectric and ferroelectric materials.This study demonstrates a novel approach to achieve ultrahigh electromechanical response in materials by inducing extreme structural instability through the competition between antiferroelectric (AFE) and ferroelectric (FE) orders. The researchers designed sodium niobate (NaNbO₃, NNO) thin films to coexist both AFE and FE phases, guided by the phase diagram and theoretical calculations. These films exhibit effective piezoelectric coefficients exceeding 5,000 pm V⁻¹ due to electric-field-induced phase transitions from AFE to FE. The results provide a general strategy for designing and exploiting antiferroelectric materials for electromechanical devices, offering significant advancements in the field of piezoelectric and ferroelectric materials.