STUDY ON THE ELECTRICAL-CONDUCTION MECHANISM OF POLYPYRROLE FILMS

The electrical conduction mechanism of polypyrrole films containing various counter ions was investigated. Above 100 K the temperature dependence of electrical conductivity obeyed the Mott equation based on variable range hopping. The exponential factor (T0) increased as the size of counter ion increased, while the pre-exponential factor (K0) was independent of the size. The enhancement of conductivity (sigma-parallel to) in the stretch direction upon stretching was explained by the increase of the hopping attempt frequency (nu-0). The temperature dependence of the conductivity of the films containing small counter ions fitted well the Sheng equation from room temperature down to 10 K suggesting that the conduction is dominated more strongly by tunneling than by hopping in a lower temperature region. The conductivity of a film containing PF6- showed a metallic-like temperature dependence below 20 K where the apparent magnetoresistance was positive.