Interplay of hopping and percolation in organic conducting blends

Electronic transport properties of organic conductive blends made of doped poly(aniline) and poly(methyl methacrylate) are studied as a function of th e conductive phase fraction p and the temperature T. As p is varied, the sc aling law of electrical percolation, sigma proportional to (p - p(c))(1), i s obeyed by the de conductivity sigma with a single value of p(c) = 0.07% f or a wide range of temperatures. Conversely, the conductivity exponent t in creases monotonically from 1.4 to 4.3 as T decreases. At constant p, the th ermal dependence of sigma is described by the superposition of a metallic p art and a hopping part. In the hopping law, In sigma proportional to -(T-0/ T)(gamma), the exponent is p dependent. Considering a wide and T dependent distribution of local conductances, we may explain the non-canonical behavi or of exponents t (continuous percolation model) and gamma.