Transport studies of protonated emeraldine polymer: A granular polymeric metal system

Abstract

An experimental study of the temperature- ($T$) dependent dc conductivity $\ensuremath{\sigma}$, the electric field ($E$) dependence of $\ensuremath{\sigma}$, and the $T$-dependent thermopower $S$ as a function of protonation level ($0.0<x\ensuremath{\equiv}\frac{[{\mathrm{H}}^{+}]}{[\mathrm{N}]}\ensuremath{\leqq}0.5$) of emeraldine polymer is presented. The conductivity $\ensuremath{\sigma}(300 \mathrm{K})$ varies from ${10}^{\ensuremath{-}10}$ to 10 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ with increasing protonation, while $\ensuremath{\sigma}(T)\ensuremath{\propto}\mathrm{exp}[\ensuremath{-}{(\frac{{T}_{0}}{T})}^{\frac{1}{2}}]$, with ${T}_{0}$ decreasing with increasing $x$. Above a threshold field ${E}_{t}$, $\ensuremath{\sigma}\ensuremath{\propto}\mathrm{exp}(\ensuremath{-}\frac{{E}_{0}}{E})$, with ${E}_{0}$ constant. The thermopower $S$ changes sign with increasing $x$ and is proportional to $T$ for $x\ensuremath{\approx}0.5$. The transport properties are the first systematic evidence for the formation of a granular polymeric metal.