A DIRECT-CURRENT PIEZOELECTRIC EFFECT IN FLUORINATED ETHYLENE-PROPYLENE COPOLYMER DUE TO SPACE-CHARGE

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