SEMICONDUCTOR-METAL TRANSITION IN DOPED (CH)X - THERMOELECTRIC-POWER

Thermoelectric power studies of polyacetylene have been carried out as a function of dopant concentration and temperature. The thermopower of pure trans-(CH)x is large (S = +850 μ V °K) and positive consistent with p-type material. With iodine doping, (CHIy)x, the thermopower remains positive over the full range of concentration 0 < y < 0.22. The semiconductor-metal transition is clearly observed at nc ≅ 3 mole %; S falls dramatically from S = +850 μ V °K at y = 0.003 to S = +30 μ V °K at y = 0.03. At higher concentrations, S remains nearly constant saturating at +18 μ V °K in the heavily doped metallic polymer. Temperature dependences are consistent with metallic behavior at the highest dopant concentrations and hopping transport in the undoped and lightly doped polymer. © 1979.