Dielectric Materials for Electrical Engineering

Chapter 23

Piezoelectric Polymers and their Applications 1

23.1. Introduction

The piezoelectric effect on a polymer was revealed for the first time in Poly(vinylidene fluoride (PVDF) by Heiji Kawaï, in 1969 [KAW 69]. In general, piezoelectricity corresponds to the outbreak, or the variation, of a polarization in a material in response to the application of a mechanical stress: a phenomenon designated as the direct effect. This type of material also produces the opposite effect: the application of an electric field causes a deformation of the sample. These electrical and mechanical properties when coupled with polymers are used in several applications, such as receiving and transmitting transducers.

PVDF and its copolymer vinylidene fluoride (VDF) with trifluoroethylene (TrFE) or tetrafluoroethylene (TFE) groups are materials whose ferroelectricity has been demonstrated [LOV 83, FUR 89], and which is developed in section 23.3.1. In these semi-crystalline polymers, it is the spontaneous polarization of the crystalline phase which causes their piezoelectricity. Fluorinated polymers have good piezoelectric properties associated with intrinsic properties of softness, lightness, etc. These organic materials thus have an interesting place in applications such as transducers, for example, in comparison with a piezoelectric ceramic, the lead zirconate titanate (PZT) which is also widely used.

More recently, ferroelectric properties have been shown in other semi-crystalline polymers: the ...