Electrical conductivity and thermopower of phosphoric acid doped polyaniline

Electrical transport properties of phosphoric acid doped polyaniline are investigated by the measurements of low temperature conductivity and thermopower. Samples were prepared by chemical polymerization of aniline in aqueous solution of phosphoric acid at various ratios of acid to aniline (Z). The conductivity at room temperature increases from 3 S/cm to 40 S/cm, and the thermopower increases from +0.2 μV/K to +7.6 μV/K, as the ratio Z varies from 1 to 6. The low temperature conductivity follows variable range hopping (VRH) temperature dependence, ln σ α - (T0/T)x, where VRH exponent systematically changes from x = 1/2 to 1/4. The thermopower changes from (U-shape to linear temperature dependence as the ratio Z increases. The systematic variation of transport data was analyzed by considering heterogeneous contributions from metallic transport and VRH process in disordered polymeric system.