Thermoelectric properties of n-type cobalt doped chalcopyrite Cu1−xCoxFeS2 and p-type eskebornite CuFeSe2

Chalcopyrite CuFeS2 has been recently suggested as a promising thermoelectric material. In the present paper, the transport properties – electrical resistivity ρ and Seebeck coefficient S – of the n-type CuFeS2 chalcopyrite and the p-type CuFeSe2 eskebornite have been measured. Very different groundstates are evidenced with a semimetallic behavior concomitant to a metal-like S(T) curve for CuFeSe2 whereas CuFeS2 is a semiconductor with much larger |S| values. For that reason, charge creation by Co2+ for Cu+ substitution in CuFeS2 has been performed. The veracity of the Co for Cu substitution for x ≤ 0.10 in Cu1−xCoxFeS2 chalcopyrite has been confirmed by EDS analyses, coupled to electron diffraction, with a transmission electron microscope. Also, this study demonstrates the existence of twinning domains. The compounds corresponding to the best compositions in terms of power factor have been densified by Spark Plasma Sintering for thermal conductivity measurements. A maximum ZT value up to 0.22 at 675 K for Cu0.96Co0.04FeS2 has been obtained.