# Enhanced polarization and abnormal flexural deformation in bent freestanding perovskite oxides

## TL;DR

Researchers found that bending freestanding perovskite oxides creates large electric polarization and unusual thickness changes, opening new possibilities for nanoelectromechanical systems.

## Contribution

The study reveals a new flexural deformation mechanism in freestanding perovskite oxides due to flexoelectricity–piezoelectricity interplay.

## Key findings

- A giant flexoelectric response was observed in bent freestanding BiFeO3 and SrTiO3 with strain gradients up to 3.5 × 10⁷ m⁻¹.
- Bent freestanding BiFeO3 showed a substantial thickness change, indicating a unique bending-expansion/shrinkage effect.
- Theoretical models attribute the deformation to a flexoelectricity–piezoelectricity interplay.

## Abstract

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.

Freestanding perovskite oxides pave the way to novel flexural properties. Here, the authors observe the nanoscale strain gradient induced flexoelectric polarization with an unusual flexo-expansion/shrinkage effect in freestanding ferroelectric oxide.