Flexoelectric polarization of piezoelectric PVDF-films above the curie temperature

A new field of research is the flexoelectric effect of solids. This quit new electromechanical energy conversion mechanism has not yet been sufficiently investigated till now. Flexoelectricity defines the change of electrical polarization induced by changing of strain gradients in dielectric materials. In contradiction to the piezoelectric effect, all dielectric materials show a flexoelectric behavior. Flexoelectric conversion is not limited to defined temperature ranges. The effect is still present above the Curie temperature of piezoelectric materials. This interesting behavior could lead to new applications in different branches. This paper describes investigations on flexoelectricity at temperatures above the Curie temperature in piezoelectric polyvinylidene difluoride (PVDF) polymer films. Changes of the mechanical strain gradient in the polymer film lead to a change of polarization. Furthermore, this leads to a charge separation on aluminum electrodes deposited on both sides of the polymer film. Finally, the charge transport to the electrodes in an external circuit can be measured. To analyze the flexoelectric polarization alone and in combination with other effects measurements were carried out at room temperature and above the Curie temperature. At temperatures of 130°C, i.e. far above the Curie temperature an unexpected strong polarization was found. It ranges between 50% and 80 % of the polarization values at room temperature.