Reversible pyroelectricity and inverse piezoelectricity in polyvinylidene fluoride

We present dc measurements of the reversible pyroelectric effect in the temperature interval 170–350 °K and of the inverse piezoelectric effect at 0.3 °K for films of commercial polyvinylidene fluoride which were polarized in a strong dc electric field at elevated temperatures. The pyroelectric coefficient dP/dT increases with temperature and exhibits slightly discontinuous changes in slope at Tg≃−50 °C and Tb≃+20 °C. At room temperature, dP/dT ∼4×10−10 C/cm2 °K. At 0.3 °K the piezolectric strain coefficient d33 measured along the thickness of the sample is of the order of −10−8 cgs, where the negative sign indicates that the film thickness decreases upon application of a dc field in the direction of the poling field. The strain coefficients in the plane, d31, are of the order of 10−9 cgs. Annealing experiments suggest that the reversible pyroelectric effect and the inverse piezoelectric effect originate from the same polarization.