Thermopower of deuterated and alloyed Cu-DCNQI-crystals — Evidences for a “quite normal reentry” of the conductivity

In Cu(2,5-DMe-DCNQI)2 (DCNQI: N,N1-Dicyanoquinonediimine) crystals with metal-like conductivity, phase transitions (ph.t.) to an insulating state can be adjusted. A reentry to the metallic state at lower temperature is observed in alloyed Cu-DCNQI systems. Correlating the ph.t. of the thermopower S, the conductivity σ and the ESR-intensity of deuterated and alloyed DCNQI salts, we could proof a model of coexisting conducting and non-conducting areas in the vicinity of the ph.t. We could find S(T) ∼ T - as known for metals - in the high temperature range for the examined DCNQI-salts. At low temperatures, in the range of the reentry of σ, S(T) reaches again the value according to a metallic behavior. This low temperature metallic state is identified as equivalent to that of the high temperature one.