Electrical conduction and dielectric relaxation in polyethylene terephthalate succinate

Electrical conduction and complex permittivity are examined in polyethylene terephthalate succinate, focusing on their relations to dielectric relaxation processes. Both the real and imaginary parts of the complex permittivity, namely, the dielectric constant έ_r and the dielectric loss factor ε_r, increase with a decrease in frequency, especially at high temperatures. They are both ascribed to the transport of ionic mobile carriers. Namely, the carrier transport forms a conduction current that should contribute to ε_r. On this occasion, if charge exchange does not occur at the two electrodes, heterocharge layers should be formed before the electrodes. This should increase the charge density on the electrodes, thus contributing to έ_r. In addition to the increase in έ_r and ε_r due to mobile ions, two relaxation processes, one due to micro-Brownian motion of dipoles and the other due to orientation and magnitude change of the dipole moment induced by two end groups in the polymer main chain, are observed. Corresponding to these two relaxation processes, two thermally stimulated discharge current (TSDC) peaks appear. The two TSDC peaks as well as the increments in έ_r and ε_r become larger when the crystallinity of the sample decreases.