Shear flexoelectric coefficient μ1211 in polyvinylidene fluoride

Defined as a strain gradient-induced electric polarization, flexoelectricity exists in all dielectric materials. The coefficient that exists between the strain gradient and the electric polarization defines the flexoelectric coefficient tensor. The tensor components along the longitudinal and transverse directions have been studied widely. However, little progress has been reported on flexoelectric properties in the shear direction to date. In this work, a novel method for measurement of the shear flexoelectric coefficient μ1211 of polyvinylidene fluoride is presented. An experiment is conducted on a tubular unpolarized specimen, where shear strain gradient is generated along the radial direction by applying torque to the ends of the tube-shaped specimen. Dynamic torque is exerted on specimens with a static bias value and at different frequencies. The generated shear strain gradient is calculated via finite element analysis and the corresponding induced electrical polarization is measured using a charge amplifier. The shear flexoelectric coefficient μ1211 is found to have an average value of 7.318 × 10−10 C/m at room temperature. The experimental results show good agreement with the theoretical predictions and indicate the potential value of this material property for electromechanical device fabrication.