Properties of polyacetylene doped with I, Br, IrCl6, and FeCl3

We have studied the temperature dependence of the resistivity of polyacetylene doped with I, Br, Ir${\mathrm{Cl}}_6$, and Fe${\mathrm{Cl}}_3$. The roles of dopant molecule size, doping technique, doping speed, and isomerization state in determining the mechanism of electrical conduction are discussed. Evidence for dopant-induced disorder is presented from x-ray and high-resolution transmission electron microscopy studies. We suggest that the dopant molecule size determines whether the dopant is dispersed molecularly or whether the dopant molecules aggregate. In addition, we find significant differences in the activation energy, $k_B{T}_0$, between $\mathrm{CH}{\left(\mathrm{Br}\right)}_y$ and $\mathrm{CH}{\left(\mathrm{I}\right)}_y$, although the characteristic temperature dependence of the resistivity is the same.