TEMPERATURE-DEPENDENCE OF SHEAR PIEZOELECTRIC PROPERTIES OF POLY(VINYLIDENE FLUORIDE) STUDIED BY PIEZOELECTRIC RESONANCE METHOD

Elastic and dielectric anisotropies, and shear piezoelectric propertie s of uniaxially oriented poly(vinylidene fluoride) (PVDF) were determi ned in the temperature range from 10 K to 400 K by a piezoelectric res onance method. The shear piezoelectric stress constant e(24) increases above the primary dispersion temperature; while e(15) decreases marke dly and tends to zero at 390 K: e(24) and e(15) are respectively, 28 m C/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 cry stalline and amorphous phases are combined in series and parallel alon g the chain axis. The analysis shows that e(15) in the crystalline pha se decreases considerably above the primary dispersion temperature, wh ereas e(24) in the crystalline phase increases with increasing tempera ture.