On the nature of the origin of the isothermal and non-isothermal current released from dielectric materials

The mechanism of the isothermal and the non-isothermal current released from a polarized/charged dielectric material is analyzed and a model is presented to account for the experimental results, including the polarity reversal of the current. Isothermal discharging current and isothermal final discharging current experiments, for samples polarized/charged at constant current or constant voltage, have been carried out. At the same time thermally stimulated discharge current measurements on partially or well-conditioned specimens charged/polarized at constant current or constant field have been carried out. The experimental measurements have been carried out on polyethylene terephthalate but the reported results are typical for a large class of materials. The currents determined by the homocharge and the heterocharge have the same polarity, no matter how high the polarization/charging field was. No current polarity reversal has been observed for a well-conditioned sample. For a partially conditioned sample the shape and the polarity of the thermally stimulated discharge currents peaks are strongly dependent about the conditioning process. Charge layers can exist into the sample accounting for the current polarity reversal. The external current is determined by the disorientation of dipoles and by the movement of the positive and/or negative space-charge clouds, or by the corresponding zero field planes, under the image force, toward the nearest electrodes. (C) 2001 Elsevier Science B.V. All rights reserved.