Materials with electromechanical coupling are essential for transducers and acoustic devices as reversible converters between mechanical and electrical energy^1,2,3,4,5,6. High electromechanical responses are typically found in materials with strong structural instabilities, conventionally achieved by two strategies—morphotropic phase boundaries⁷ and nanoscale structural heterogeneity⁸. Here we demonstrate a different strategy to accomplish ultrahigh electromechanical response by inducing extreme structural instability from competing antiferroelectric and ferroelectric orders. Guided by the phase diagram and theoretical calculations, we designed the coexistence of antiferroelectric orthorhombic and ferroelectric rhombohedral phases in sodium niobate thin films. These films show effective piezoelectric coefficients above 5,000 pm V⁻¹ because of electric-field-induced antiferroelectric–ferroelectric phase transitions. Our results provide a general approach to design and exploit antiferroelectric materials for electromechanical devices.

具有机电耦合的材料对于作为机械能和电能之间的可逆转换器的换能器和声学器件至关重要^1,2,3,4,5,6 。高机电响应通常出现在具有强结构不稳定性的材料中，通常通过两种策略来实现：同形相界⁷和纳米级结构异质性⁸ 。在这里，我们展示了一种不同的策略，通过竞争的反铁电和铁电级诱导极端结构不稳定来实现超高机电响应。在相图和理论计算的指导下，我们设计了铌酸钠薄膜中反铁电斜方相和铁电菱方相的共存。由于电场引起的反铁电-铁电相变，这些薄膜显示出高于 5,000 pm V ^{-1 的}有效压电系数。我们的结果提供了设计和开发机电设备反铁电材料的通用方法。