Thermoelectric properties of the chalcopyrite Cu1-xMxFeS2-y series (M = Mn, Co, Ni)

The natural chalcopyrite mineral CuFeS2 is a semiconductor material with potential for thermoelectric applications. This study presents the thermoelectric properties - electrical resistivity rho, Seebeck coefficient S and thermal conductivity kappa - of the substituted on the Cu site and/or sulfur deficient CuFeS2 chalcopyrite based series Cu(1-x)Mx(F)eS(2-y) (M = Mn, Co, Ni, x <= 0.05 and y <= 0.02). All samples have been densified by spark plasma sintering, allowing proper measurements of S, rho and kappa at high temperature. All compounds show n-type semiconducting properties with large absolute values of S, from -220 to -340 mu V K-1. Maximum ZT values up to 0.20 at 623 K were obtained for Cu0.97Mn0.03FeS2 and Cu0.98Co0.02FeS1.98. The veracity of Mn for Cu substitution into the structure has been confirmed by EDS analyses, coupled to electron diffraction within a transmission electron microscope. The latter study demonstrates the existence of twinned domains. The thermal conductivity reaches values as low as kappa similar to 1.2 W m(-1) K-1 at 623 K. The magnetic properties of a Mn substituted sample did not show any significant modification in the magnetic behavior compared to the pristine CuFeS2 compound. The small negative magnetoresistance observed in CuFeS2 of about -2% at 5 K in 9 T is degraded in the Mn substituted sample.