Recent realizations of ultrathin freestanding perovskite oxides offer a unique platform to probe novel properties in two-dimensional oxides. Here, we observe a giant flexoelectric response in freestanding BiFeO₃ and SrTiO₃ in their bent state arising from strain gradients up to 3.5 × 10⁷ m⁻¹, suggesting a promising approach for realizing ultra-large polarizations. Additionally, a substantial change in membrane thickness is discovered in bent freestanding BiFeO₃, which implies an unusual bending-expansion/shrinkage effect in the ferroelectric membrane that has never been seen before in crystalline materials. Our theoretical model reveals that this unprecedented flexural deformation within the membrane is attributable to a flexoelectricity–piezoelectricity interplay. The finding unveils intriguing nanoscale electromechanical properties and provides guidance for their practical applications in flexible nanoelectromechanical systems.

最近实现的超薄独立钙钛矿氧化物为探索二维氧化物的新特性提供了一个独特的平台。在这里，我们观察到由高达 3.5 × 10 ⁷  m ^-1的应变梯度引起的独立式 BiFeO ₃和 SrTiO ₃在其弯曲状态下的巨大挠曲电响应，这表明了实现超大极化的有希望的方法。此外，在弯曲的独立式 BiFeO _{3中发现了膜厚度的显着变化}，这意味着铁电膜中存在一种不寻常的弯曲膨胀/收缩效应，这是以前在晶体材料中从未见过的。我们的理论模型表明，膜内这种前所未有的弯曲变形可归因于挠曲电 - 压电相互作用。这一发现揭示了有趣的纳米级机电特性，并为它们在柔性纳米机电系统中的实际应用提供了指导。