Thermal depolarization of PVDF: anomaly at 180°C

PVDF samples with high β 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 after cooling down again to room temperature For elevated temperatures up to 175°C the polarization was reduced to 2% of the original value, yet recovered roughly to 8% of the original value after cooling down to room temperature In contrast to this, when heating the films to 180°C, a significantly different behavior was observed in cooling down to room temperature again the polarization returned from ~1% at 180°C to ~40% of the original prepolarized value