Enhanced flexoelectricity with pre-strain gradients

Flexoelectricity describes a strain-gradient-induced electrical polarization in dielectric materials. Compared with piezoelectricity, flexoelectricity has some advantages in size dependence, material range, and temperature range, although its electro-mechanical efficiency is low. Flexoelectric enhancement is to be achieved principally by reducing dimensions and enlarging flexoelectric coefficients. In this work, we propose a mechanical approach to enhance flexoelectricity by adjusting a pre-strain gradient with bending moments. Based on theoretical analysis, the relationship between the pre-strain gradient and enhanced polarization is deduced. Performing a four-point bending approach, experimental verification is achieved by measuring polarized charges of non-poled polyvinylidene fluoride films. The measured electric polarization has been increased by 2.8 times by adjustment of pre-strain gradients. This demonstrates the feasibility of enhancing flexoelectricity by mechanical means.