Thermoelectric power studies of organic conducting composites (BEDT-TTF)x/Y (Y = I, AuI, AuI3) and (BEDO-TTF)x/I

The results of studies on the thermoelectric power of organic composites formed by a direct charge transfer reaction in the solid state, of general formula (BEDT-TTF)x/Y (Y = I, AuI, AuI3) and (BEDO-TTF)x/I, where BEDT-TTF means bis-(ethylenedithio)tetrathiafulvalene and BEDO-TTF is bis-(ethylenedioxy)tetrathiafulvalene, are presented. It is shown that the thermoelectric power of these materials arises mainly from the contribution of the conducting grains (BEDT-TTF)2I3 and (BEDT-TTF)2AuI2 in (BEDT-TTF)x/Y composites and the grains (BEDO-TTF)2.4I3 in (BEDO-TTF)x/I composites. The contribution of the insulating intergrain phase is small for x ≅ xopt. The results are consistent with predictions of effective-medium theory for thermoelectric power in inhomogeneous materials. The conclusion is that the thermoelectric properties of grains in highly conducting composites are nearly the same as the properties of the single crystals