Crossover from Mott to Efros-Shklovskii variable-range-hopping conductivity in conducting polyaniline

Electrical resistance and magnetoresistance of the HCl-doped polyaniline (PANI) in aqueous ethanol have been investigated at low temperature down to 1.8 K and in magnetic field up to 8 T. The weaker temperature dependence of resistivity characterized by the ratio, ϱr= ϱ(1.8 K) / ϱ(300 K) indicates that a better homogeneity and less disorder can be obtained by protonation with HCl in ethanol media. The samples with resistivity ratio lying in the range 102≤ϱr≤103 exhibit a crossover from Mott to Efros-Shklovskii variable-range-hopping (VRH) conduction below 10 K. The Coulomb gap energy has been calculated and is small (0.22–0.04 meV).