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 fro m a polarized/charged dielectric material is analyzed and a model is presen ted to account for the experimental results, including the polarity reversa l of the current. Isothermal discharging current and isothermal final disch arging current experiments, for samples polarized/charged at constant curre nt or constant voltage, have been carried out. At the same time thermally s timulated discharge current measurements on partially or well-conditioned s pecimens charged/polarized at constant current or constant field have been carried out. The experimental measurements have been carried out on polyeth ylene terephthalate but the reported results are typical for a large class of materials. The currents determined by the homocharge and the heterocharg e have the same polarity, no matter how high the polarization/charging fiel d was. No current polarity reversal has been observed for a well-conditione d sample. For a partially conditioned sample the shape and the polarity of the thermally stimulated discharge currents peaks are strongly dependent ab out the conditioning process. Charge layers can exist into the sample accou nting for the current polarity reversal. The external current is determined by the disorientation of dipoles and by the movement of the positive and/o r negative space-charge clouds, or by the corresponding zero field planes, under the image force, toward the nearest electrodes. (C) 2001 Elsevier Sci ence B.V. All rights reserved.