Low frequency dielectric relaxation phenomena in conducting polypyrrole and conducting polypyrrole-zeolite composites

The dielectric properties of polypyrrole-zeolite composites up to 50% w/w zeolite are studied in the frequency range from 10(-2) to 2x10(6) Hz from room temperature to liquid nitrogen temperature. The complex permittivity formalism reveals a temperature dependent relaxation in all samples except for the 25% w/w zeolite composite. The frequency f(max) where a maximum of a loss peak is located varies with temperature by the Williams-Lander-Ferry law. The values of the activation energy of the relaxation process (which are of the order of polaronic dc conductivity) have the tendency to reach a minimum in the 25% w/w composition, which is a loss-free composite. The 50% w/w zeolite behaves as a dielectric where ionic relaxation dominates. The temperature variation of the strength of the dielectric mechanism follows a Curie law, apart from 50% w/w zeolite where the dielectric strength is practically constant. The frequencies, where loss peaks are maximum, as well as dc conductivity follow qualitatively the same temperature law, but the parameters are quite different. Moreover, the locations of the relaxation peaks diverge from the predictions of Barton-Nakajima-Namikawa model. Long-range electric charge transport (dc conductivity) and the relaxation that corresponds to short-range localized motion probably involve different processes. (C) 2004 American Institute of Physics.