Thermal depolarization of PVDF: anomaly at 180 degrees C

PVDF (polyvinylidene fluoride) samples with high beta -content (80%), prepolarized at room temperature, were heated to higher temperatures. The polarization was measured first under open circuit conditions at the high temperature and then cooling down again to room temperature. For elevated temperatures up to 175 degrees C the polarization is reduced to 2% of the original value, yet covers roughly to 8% of the original value after cooling down again to room temperature. In contrast, when heating up the films to 180 degrees C a significantly different behavior was observed: in cooling down to room temperature the polarization returns from about 1% at 180 degrees C to about 40% of the original prepolarized value.<
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