COMPARED TEMPERATURE-DEPENDENCE OF THE ELECTRICAL-CONDUCTIVITY OF UNORIENTED AND STRETCHED POLYACETYLENES DOPED WITH HEAVY ALKALI-METALS

Classical unoriented (CH)x synthesized using the technique of Ito et al. and highly oriented polyacetylene (HOPA) obtained after a method similar to that proposed by Akagi et al. were doped to saturation with heavy alkali metal in the vapour phase. RT electrical conductivities in HOPA-based materials are 10 times higher than the values measured from doped-unoriented compounds. The thermal dependence of sigma in the range 4.2 - 290 K is strongly dependent on the nature of the polymer used. In unoriented materials, the conductivity obeys a fluctuation induced tunneling model, as proposed by Sheng, in a large domain of temperatures. To the contrary, the tridimensional variable range hopping is perfectly applicable to heavily doped HOPA compounds.