Electrical conductivity effects in polyethylene terephthalate films

Electrical conductivity effects in biaxially stretched polyethylene terepht halate (PET) films of 6 mu m thickness and 68% degree of crystallinity were investigated by means of dielectric relaxation spectroscopy in the frequen cy range 10(-2)-10(6) Hz and at temperatures higher than the glass transiti on temperature (similar to 85 degrees C) up to 190 degrees C. The formalism s of complex permittivity, electric modulus, and impedance were employed to analyze the experimental data. The results are discussed in terms of dc co nductivity, conductivity current relaxation, interfacial Maxwell-Wagner-Sil lars polarization, rho peak, space-charge polarization, and electrode polar ization. They are compared with the predictions of models for the electrica l and dielectric properties of ion-conducting polymers. The dc conductivity values determined from dc measurement, from ac conductivity plots and from complex impedance plots agree well with each other. Their temperature depe ndence is described by the Vogel-Tammann-Fulcher equation and classifies PE T as a fragile system. (C) 2000 American Institute of Physics. [S0021-8979( 00)01206-8].