Electrical conduction in polyethylene terephthalate and polyethylene films

Electrical conduction is studied in polyethylene terephthalate and to a limited extent in polyethylene over a range of fields up to 1·2×10⁶ V cm⁻¹. In common with previous investigations, it is found that the current decays with time according to an inverse power law, but this can be obviated by a conditioning procedure which then allows steady values of current to be measured over a range of temperature and field. The results suggest that the current has an activation energy which is field dependent, but attempts to fit the results to a Schottky-type law are not very successful.

By adopting a more generalized form of potential barrier than the coulombic one usually chosen in the Schottky law, it is possible to obtain consistent agreement with experiment. The form of potential barrier chosen appears to refer to the cathode-dielectric interface and is probably determined by space charge in the dielectric. Values of the metal-dielectric contact potential for the samples of polyethylene terephthalate and polyethylene investigated were 2·58 and 2·14 eV respectively for aluminium electrodes. It is suggested that the time dependence observed before conditioning is completed is due to the slow build-up of the full interfacial barrier.