Phase transformations and ordering in polyacetylene

Abstract

Donor and acceptor complexes of polyacetylene containing the counterions ${\mathrm{K}}^{+}$, ${\mathrm{Na}}^{+}$, and ${\mathrm{PF}}_{6}$${\mathrm{}}^{\mathrm{\ensuremath{-}}}$ have been investigated by electrochemical methods. First-order structural phase transformations as well as counterion-ordering transitions within structural phases have been identified for alkali-metal complexes of polyacetylene. The conductivities of the complexes exhibit relative maxima at the compositions of ordered phases. Ordered phases of ${\mathrm{CHNa}}_{\mathrm{y}}$ have been identified at compositions y=0.0667, 0.0833, and 0.111; ordered phases of ${\mathrm{CHK}}_{\mathrm{y}}$ are found at y=0.0625, 0.0833, 0.125, and 0.167. Evidence is found for disproportionation into separate phases at intermediate doping levels, 0.003<y<0.06. Conductivity \ensuremath{\sigma} at these intermediate levels is a strongly varying function of y. In this range, \ensuremath{\sigma} versus y data are well fitted by a variable-range-hopping model.