Pyroelectric and switching properties of polyvinylidene fluoride film

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Abstract
A P-E hysteresis loop is observed in polyvinylidene fluoride film with a spontaneous polarization of 8 μcoul/cm2at 140°C. The spontaneous polarization, obtained by the integration of the pyroelectric current, decreases with increase in temperature. The pyroelectric current shows a minimum at the solid-to-glass transition temperature (-40°C). The dielectric constant at 25°C, measured at -.003 Hz, is -1000, or two orders of magnitude larger than the value measured at 50 Hz. The switching current above 120° C has the form Jmax = JoEne - α/kT with n varying from 0.7 to 1.6 and α equal to 0.65 eV. The inverse switching time shows a similar dependence on field and temperature, with an activation energy of 1 eV. The long switching time, of the order of several minutes at 150°C, suggests that polarization reversal is associated with the rotation of the long chain molecules by the applied field.