Temperature dependence of mobility of conducting polymer polyaniline with secondary dopant

The conductivity $\sigma$ and carrier density $n$ of the conducting polymer polyaniline were investigated by changing the concentration $x$ of a secondary dopant, meta-cresol. We found that $\sigma$ changes by four orders of magnitude within the $x$-range of 1-10 %, while $n$, as estimated from the Hall measurements, shows a weak dependence on $x$ in the region of 2% <$x$< 50%. These results suggest that $\sigma$ can be enhanced by the change in the mobility $\mu$. We analyzed the temperature dependence of $\mu$ by not only the combination of two different types of scattering mechanism, but also by the polaron hopping model. The experimental data of $\mu(T)$ can be explained well by the latter model with reasonable fitting parameter values of a small-polaron binding energy and a longitudinal optical phonon frequency.