Transversal Flexoelectricity of Semiconductor Thinfilm under High Strain Gradient

TL;DR

This paper theoretically investigates the transversal flexoelectric effects in bent MgO thin films under high strain gradients, revealing nonlinear elastic behavior and anisotropic flexoelectric responses with implications for ionic solids.

Contribution

It introduces a theoretical approach using the generalized Bloch theorem to analyze flexoelectricity in MgO thin films under high strain gradients, highlighting nonlinear elastic effects and anisotropic responses.

Findings

Nonlinear elastic behavior under high strain gradients.

Large internal displacements lead to strong polarization.

Anisotropic flexoelectric coefficients between (100) and (111) films.

Abstract

The flexoelectric behaviors of solids under high strain gradient can be distinct from that under low strain gradient. Using the generalized Bloch theorem, we investigate theoretically the transversal flexoelectric effects in bent MgO thinfilms. As a comparison, a centrosymmetric (100) film and a non-centrosymmetric (111) film are considered. Under bending, the mechanical responses of both films are linear elastic under low strain gradient but nonlinear elastic under high strain gradient. In the linear elastic regime, no internal displacements and thus no polarization contributed from ions are induced. Only in the nonlinear elastic regime, atoms adopt discernibly large internal displacements, leading to strong polarization from ions. Because the internal displacements of atoms of the (111) film are much larger than those of the (100) film, the obtained flexoelectric coefficient of the (111) film is also greater than that of the (100) film, revealing strong anisotropy of flexoelectricity of MgO film. Our results and the employed approach have important implications for the study of flexoelectric properteis of ionic solids.