Anomalous discharge current in copolymers of vinylidene fluoride and trifluoroethylene

When a steady or step voltage is applied to a dielectric material, the transient charge current decreases with time from the initial value to a leveled-off value that represents the leakage current arising from the conductivity of material. The transient discharge current is the same as the charge current remaining after subtracting the leakage current. Unlike ordinary charging and discharging processes, anomalous behavior was observed for copolymers of vinylidene fluoride and trifluoroethylene with varied comonomer content in which a current peak took place in a discharge process. The time taken for the current peak to appear is shorter the higher the temperature. This unusual discharging occurred at temperatures above the ferroelectric transition and was considerably suppressed in electrodialysed samples with less ionic impurity content. Thus the anomalous discharge process is most likely connected with a retarded discharge of ionic charge bound in the paraelectric phase