Low-energy conductivity of PF6-doped polypyrrole

In this paper we present a set of temperature-dependent reflectivity;Ind de conductivity measurements on a series of PF6-doped polypyrrole samples dif fering only in their synthesis temperatures, spanning the metal-insulator t ransition. From the reflectivity we have derived optical constants, taking particular care that they are Kramers-Kronig consistent. We have analyzed o ur data in the light of two proposed models for the structure of conducting polymers, homogeneous and inhomogeneous disorder, and find that the observ ed decrease in the low-energy ac conductivity can be accounted for by a sim ple generalization of the heterogeneous disorder model used to explain the de conductivity. The homogeneous localization-modified Drude model fails to satisfactorily model the ac conductivity at low energy. [S0163-1829(99)060 43-9].