The nature of polarization and piezoelectric properties of a vinylidene fluoride-tetrafluoroethylene copolymer

The piezoelectric properties of a vinylidene fluoride-tetrafluoroethylene copolymer can be explained either by orientation of the β-crystallite dipoles in the field of injected charges or by the presence of a ferroelectric phase in the polymer, depending on the sample polarization conditions. Upon the polarization of three-layer film samples, the inversion of thermostimulated depolarization (TSD) current in the middle layer was observed at 368-403 K and that in the anode layer at 428 K. The inversion peaks can be related primarily to the injection of positive charges into the polymer. It is demonstrated that effective polarization takes place predominantly at the anode layer. A correlation was established between a change in the TSD peak intensity and the d 31 piezoelectric modulus on the one hand and the (110) diffraction intensity on the other hand. It was found that the values of the d 33 piezoelectric modulus are greater than d 31 , irrespective of the sample polarization method.