ESR study of the electrochemical doping of polyacetylene with potassium

In this study we present the first experimental evidence of staging during doping of ${\left(\mathrm{CH}\right)}_x$ with potassium, obtained from ESR measurements. For that purpose, we have followed the peak-to-peak linewidth of the ESR signal during successive electrochemical doping-undoping cycles. We have also measured the open-circuit potential difference $V_{\mathrm{oc}}$ of the cell. The behavior of the linewidth related to $V_{\mathrm{oc}}$ shows that doping and undoping occur via a sequence of successive ordered phases corresponding to various intercalation stages: A simplified model of a pseudobiphasic system can explain qualitatively the variations of the linewidth. However, the observed behavior demonstrates the existence of an ordered phase at a doping level of 2%, during the undoping process, which is not revealed from the variations of $V_{\mathrm{oc}}$.