Study of pyroelectric and relaxation phenomena in poly(vinylidene fluoride) using thermal current analysis

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Abstract
Using the thermal current analysis (TCA) technique, pyroelectric and relaxation currents have been simultaneously measured in a number of commercial corona-poled PVdF films, over the temperature range 0-120 degrees C. A relaxation peak observed at approximately=55 degrees C is attributed to space charge residing at the crystal/amorphous boundaries of beta -crystallites, resulting in partial dipole cancellation. Annealing films at 60 degrees C removes these charges and produces an enhancement of about 10% in pyroelectricity (measured at 25 degrees C), which subsequently decays with a time constant of about 2 h at room temperature. A second relaxation peak is observed at about 80 degrees C and, although its origin is undetermined, pyroelectric measurements suggest that the underlying mechanism may also be responsible for about 10% of the pyroelectric activity possessed by a new sample.