Electronic-Properties Of Isostructural Organic Conductors (Et)(3)(Hso4)(2) And [Ni(Dddt)(2)](3)(Hso4)(2) - Thermopower And Tight-Binding Calculations

The temperature dependence of thermopower of isostructural molecular conductors [Ni(dddt)(2)](3)(HSO4)(2) and (ET)(3)(HSO4)(2) has been investigated. Drastic difference in S(T) dependences is qualitatively explained on basis of tight binding band structure calculations. A peak at 25 K in [Ni(dddt)(2)](3)(HSO4)(2) was shown to be manifestation of metal to semimetal phase transition, and the abrupt decrease at 125 K in (ET)(3)(HSO4)(2) is concerned with metal to insulator phase transition. Rather complex semimetal band structure was found in both cases.