Probing flexoelectricity via a split Hopkinson pressure bar experiment

摘要

Flexoelectricity is thought of as a universal property of all dielectric materials that couples polarization with the inhomogeneous deformation. However, at the macroscale, this coupling is usually very weak and the direct observation of flexoelectricity always suffers from a low signal-to-noise ratio (SNR). At the micron or submicron scale, both the flexoelectric effect and some surface effects may get pronounced simultaneously. To separate the flexoelectric effect from those surface effects and accurately measure the bulk flexoelectric coefficients are challenging. In this paper, we propose a high SNR method for measuring the bulk flexoelectric coefficient 11 of millimeter-sized samples through split Hopkinson pressure bar (SHPB) experiments. Our experimental results show that for a normal impact speed (17 m/s) of the striker bar, the induced voltage difference is as high as 70 mV, which can be easily measured without using signal amplifiers. In most of previous works on measuring flexoelectric coefficients, strain gradients are introduced through the design of samples' shape such as thin beams, thin films, truncated cones and pyramids. In a different way, the proposed SHPB based approach introduces time varied strains to the system and then converts time gradients of strains into their spatial gradients through elastic waves. As a promising way of measuring bulk flexoelectric coefficients, this approach produces high SNR flexoelectric signals, reduces interferences from surface effects, and avoids difficulties in fabricating nanostructures. Published by AIP Publishing.