Temperature dependence of shear piezoelectric properties of poly(vinylidene fluoride) studied by piezoelectric resonance method

Elastic and dielectric anisotropies, and shear piezoelectric properties of uniaxially oriented poly(vinylidene fluoride) (PVDF) were determined in the temperature range from 10 K to 400 K by a piezoelectric resonance method. The shear piezoelectric stress constant e 24 increases above the primary dispersion temperature, while e 15 decreases markedly and tends to zero at 390 K: e 24 and e 15 are, respectively, 28 mC/m 2 and 38 mC/m 2 at 10 K, and 48 mC/m 2 and 15 mC/m 2 at 295 K (where the coordinate axes X and Z in the film refer to the stretching axis and poling axis, respectively). The temperature dependences of e 24 and e 15 are analyzed on the basis of the model in which the crystalline and amorphous phases are combined in series and parallel along the chain axis. The analysis shows that e 15 in the crystalline phase decreases considerably above the primary dispersion temperature, whereas e 24 in the crystalline phase increases with increasing temperature.