Piezoelectricity analysis in VDF-TrFE copolymer films using the pressure wave propagation method

The pressure wave propagation method was used to study the polarization of VDF-TrFE (75-25%) copolymer films, by measuring the homogeneity, within the bulk of the material, of the piezoelectric coefficient and its relative amplitude. The influence of the value of the poling field and of the duration of the polarization process, associated with various thermal treatments, is investigated for 150-μm-thick films. When no thermal treatment is applied prior to the polarization process, the polarization is nonuniform at low field (0.3 MV/cm) and its buildup is rather slow. A fast response to the poling field is observed in films previously heated above the Curie point, and for applied fields equal to 0.7 MV/cm. In this case the polarization is uniform, even for low applied fields. Moreover, this polarization is very stable