Thermal degradation of the dielectric relaxation of 10–90% (w/w) zeolite-conducting polypyrrole composites

Abstract

The effect of thermal aging of 10–90 wt% zeolite-conducting polypyrrole composite on its dielectric properties is studied in the frequency range 10 −2 to 2 × 10 6 Hz from room temperature to liquid nitrogen temperature. A dielectric relaxation mechanism, which appears in the fresh samples, is influenced by the thermal annealing. The frequency f max where a maximum of a dielectric loss peak is located decays exponentially with the aging time and the intensity of the loss peaks shows a maximum at intermediate aging time. A modified Williams–Landel–Ferry law describes the temperature variation of f max in all specimens. Increasing activation energy values on increasing the aging duration are obtained. The temperature dependence of f max and the activation energy (regarded as the height of a potential barrier) are different from those characterizing the macroscopic conductivity, which is described by the charging energy limited tunneling model. The intensity of the dielectric mechanism in thermally treated samples deviates from the linear decrease with inverse temperature occurring in fresh polypyrrole. Although the thermal degradation of the logarithm of the dc conductivity decays proportional with the root of the aging time, the equivalent conductivity obtained from the dielectric data decays exponentially with aging duration. Time constants are obtained in both cases. The model of Barton–Nakajima–Namikawa (BNN) can hardly interconnect the dc conductivity with the relaxation process in fresh sample. The divergence augments with the aging time. The thermal aging law and the inadequacy of the BNN model probably indicates that the dc process is probably irrelevant to the relaxation process.