Long aging time thermal degradation of the ac conductivity and complex   permittivity of conducting polypyrrole
  The modification of the ac conductivity and the complex permittivity of conducting polypyrrole was monitored throughout a two years thermal aging at 343K. Reduction of the cross-over frequency is correlated with the degradation of dc-conductivity, while the ac conductivity region corresponding to the so-called 'universal' dielectric relaxation remains practically invariant during the first year of ageing, which implies a collective co-operativity among multiple degradation processes that yield a practically time-independent effective disordered environment. A broad dielectric loss peak recorded in fresh specimens splits into two distinct relaxations for intermediate stages of the annealing process. The ageing-time evolution of the dc component and the relaxations are qualitatively analysed and time constants are determined. 
I. Sakellis, A.N. Papathanassiou and J. Grammatikakis
cond-mat.mtrl-sci cond-mat.dis-nn