FREQUENCY AND TEMPERATURE SCALING IN THE CONDUCTIVITY AND ITS STRUCTURAL CONSEQUENCES

We have studied the temperature (T) and frequency (omega/2 pi) depende nce of the complex conductivity sigma(omega,T) of several systems wher e hopping conduction is dominant: conducting carbon-black/polymer comp osites as a function of carbon-black (CB) concentration, aggregates of molecular cluster compounds as a function of the size and of the dist ance between the metal cores and polymers as a function of degree of d oping. For all compounds the conductivity ar a function of omega and T can be scaled onto single curves. Using an extension of the anomalous diffusion model the specific details of these curves for the CB compo sites are shown to he characteristic of the underlying fractal structu re. The main features of the scaled dependence of sigma(omega,T) of th e randomly packed cluster compounds are well described by effective me dium theories, except at low frequencies where percolation effects bec ome important. Similar features are seer in polythiophene derivatives at doping levels above the percolation threshold.