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

Abstract

The natural chalcopyrite mineral CuFeS₂ is a semiconductor material with potential for thermoelectric applications. This study presents the thermoelectric properties – electrical resistivity ρ, Seebeck coefficient S and thermal conductivity κ – of the substituted on the Cu site and/or sulfur deficient CuFeS₂ chalcopyrite based series Cu_1−xM_xFeS_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, ρ and κ at high temperature. All compounds show n-type semiconducting properties with large absolute values of S, from −220 to −340 μV K⁻¹. Maximum ZT values up to 0.20 at 623 K were obtained for Cu_0.97Mn_0.03FeS₂ and Cu_0.98Co_0.02FeS_1.98. 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 κ ∼ 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.