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

An experimental study of the temperature- ($T$) dependent dc conductivity $\sigma$, the electric field ($E$) dependence of $\sigma$, and the $T$-dependent thermopower $S$ as a function of protonation level ($0.0<x\equiv \frac{\left[{\mathrm{H}}^{+}\right]}{\left[\mathrm{N}\right]}\leqq 0.5$) of emeraldine polymer is presented. The conductivity $\sigma \left(300\mathrm{} \mathrm{K}\right)$ varies from ${10}^{-10\mathrm{}}$ to 10 ${\mathrm{\Omega }}^{-1\mathrm{}}$ ${\mathrm{cm}}^{-1\mathrm{}}$ with increasing protonation, while $\sigma \mathrm{}\left(T\right)\mathrm{}\propto \exp [-{\left(\frac{T_0}{T}\right)}^{\frac{1}{2}}]$, with $T_0$ decreasing with increasing $x$. Above a threshold field $E_t$, $\sigma \propto \exp (-\frac{E_0}{E})$, with $E_0$ constant. The thermopower $S$ changes sign with increasing $x$ and is proportional to $T$ for $x\approx 0.5$. The transport properties are the first systematic evidence for the formation of a granular polymeric metal.