POLARONIC HOPPING CONDUCTION IN POLY(N-METHYL PYRROLE-PYRROLE) COPOLYMER

The measured ac conductivity sigma(m)(omega) and dielectric constant e psilon'(omega) of lightly doped poly(N-methyl pyrrole-pyrrole) copolym er were investigated in the temperature range 77-350 K and in the freq uency range 100 Hz-100 kHz. At low temperatures, the measured ac condu ctivity shows a strong dependence on frequency and is almost independe nt of temperature and can be described by the relation sigma(omega) = A omega(s), where the exponent s is found to be less than unity. The o bserved temperature and frequency dependence of the ac conductivity si gma(omega) can be qualitatively explained by considering contributions from two mechanisms, one giving a linear dependence of conductivity o n frequency and the other giving rise to a broad dielectric loss peak having a distribution of relaxation times. At high temperatures the di electric constant shows a frequency dispersion consistent with Debye-t ype relaxation. The origin of this relaxation was critically analysed. The estimated value of site spacing d calculated from the dielectric strength and spin density is approximate to 19 Angstrom which suggests one charge carrier per 4-6 pyrrole rings.