Analysis of electric conduction mechanisms in polyethylene terephthalate

Abstract

The isothermal current–voltage measurements on insulating materials can be improved by using a symmetric triangular signal. The measured current is field dependent and the Richardson–Schottky, the Fowler–Nordheim, the Poole–Frenkel, Ohm, space charge limited current and ionic current mechanisms can be used for the interpretation of the results. The experimental data can fit with two or more from the presented mechanisms. In deciding which is the best mechanism, it is necessary to use a second condition. We propose to use the slope of the Richardson–Schottky and the Poole–Frenkel plots to calculate the dielectric permittivity of the sample. For high fields the work function can be determined from the Fowler–Nordheim plot and can be used as a control parameter. Polyethylene terephthalate was used as standard material to test the validity of these models under moderate electric fields (0.5 MV m−1<E<20 MV m−1). For low fields Ohm's law describes the current flow. The Richardson–Schottky law is adequate only for a small field range. The Poole–Frenkel law fits best the experimental data. For high fields the Fowler–Nordheim law fits as well the experimental results. The charge accumulated in the sample strongly influences the measured current.