Temperature dependence of the pyroelectric coefficient in polyvinylidene fluoride

Abstract

The pyroelectric properties of bioriented β-PVDF were studied in the temperature range [- 100-70°C]. The temperature dependence of the pyroelectric coefficient was obtained, and its variation was compared with the DSC thermogram and the TSC complex spectrum. Three transitions have been observed in the investigated temperature range. They have been associated with the glass transition of the free and constrained amorphous phases (Tgl = -40°C and Tgu = 15°C) and to conformational reorganizations at the crystallites surface (Tac = 47°C). A correlation has been established between these pyroelectric transitions and volumetric variations. Dimensional effects have been found to reasonably describe the increase of the pyroelectric coefficient through the glass transition range. These changes in the thickness of the film correspond to secondary pyroelectricity and explain nearly 50% of the room temperature coefficient. In the glassy state, primary pyroelectricity is dominant.