Anomalous discharge current in copolymers of vinylidenefluoride and trifluoroethylene

Charge and discharge processes were studied for copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with TrFE content of 27 to 63 mol.% by use of a step-voltage field. Unlike the ordinary charge and discharge processes in polymer dielectrics, anomalous behavior was observed for copolymers of VDF and TrFE with varied comonomer content in which a current peak took place in a discharge process. The peak time, i.e., the time elapsed for the current peak to appear in a discharge transient, depended strongly on temperature and the applied field. The higher the temperature and the lower the field on charging, the shorter was the peak time. This unusual discharge process showing a current peak occurred at higher temperatures above the ferroelectric to paraelectric transition or the Curie transition of the VDF/TrFE copolymer, being much suppressed in electrodialyzed samples with less ionic impurity. Thus the anomalous discharge process is probably connected with a retarded discharge process of ionic charge bound in the paraelectric phase of the copolymer.<
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