A direct current piezoelectric effect in fluorinated ethylene-propylene copolymer due to space charge

A dc piezoelectric effect was observed in corona charged fluorinated ethylene-propylene membranes. After an appropriate thermal treatment the charge deposited on the sample surface penetrated the bulk material, with the charge centroid remaining at the center of the sample was indicated by heat pulse measurements. The charged sample responded to an applied pressure with a constant voltage signal or, if in short circuit, with a transient external electric current. This phenomenon was interpreted as being caused by a relative movement of the stored charges with respect to the material structure. A semiquantitative analysis based on this relative movement was carried out that allowed physical parameters such as the volumetric charge density and the longitudinal piezoelectric coefficient to be obtained. (C) 1996 American Institute of Physics.