Polyethylene terephthalate (PETP) foams as ferroelectrets

Voided space-charge electrets represent a new class of piezoelectric materials, the so-called ferroelectrets. Several polymers are under investigation with respect to possible ferroelectret properties. However, processing limitations, difficulties in preparing suitably voided polymer films or unfavorable property combinations often prevent the successful generation of new ferroelectrets. Here, we describe the preparation of voided polyethylene terephthalate (PETP) ferroelectret films by means of carbon-dioxide gas diffusion. First results are discussed regarding the structural and piezoelectric properties of voided PETP films. The observed piezoelectric properties of the new voided PETP films clearly demonstrate their ferroelectret behavior. It is possible to adjust the electromechanical and elastic properties over a rather wide range so that the films are suitable for several transducer applications.