Complex conductivity of polyacetylene films prepared by different methods

Abstract

The frequency (f) and temperature (T) dependence of the complex conductivity ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ was measured for undoped and lightly doped films of highly stretchable polyacetylene (hs-PA) and Shirakawa polyacetylene (S-PA). When ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ and f were reduced by using the dc conductivity \ensuremath{\sigma}(0), all the experimental data of ${\mathrm{\ensuremath{\sigma}}}^{\mathrm{*}}$ of hs-PA were on a master curve whereas those of S-PA did not show such universality. The data analysis based on the conductivity relaxation formalism revealed that the functional form H(\ensuremath{\tau})\ensuremath{\propto}${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{\alpha}}}$ (${\mathrm{\ensuremath{\tau}}}_{\mathrm{min}}$${\mathrm{\ensuremath{\tau}}}_{\mathrm{max}}$, -11) of the relaxation spectrum H(\ensuremath{\tau}), i.e., the distribution function of relaxation time \ensuremath{\tau}, fitted the experimental data best and that \ensuremath{\alpha} was independent of T for hs-PA while \ensuremath{\alpha} was proportional to T for S-PA. The T-independent \ensuremath{\alpha} for hs-PA indicates isoenergetic hopping between equivalent sites, so that the conduction mechanism in hs-PA can be ascribed to acoustic-phonon-assisted hopping of charged solitons between PA chains. On the other hand, it is likely that the inter-fibril-barrier hopping makes the main contribution to the conduction mechanism in S-PA. This difference in conduction mechanisms between hs-PA and S-PA is attributed to their morphological dissimilarities.