Evaluation of the f-electron rare-earth copper telluride GdCu1+xTe2 as a thermoelectric material

Abstract Chalcogenide compounds of composition ABX 2 (with A, B, representing metal elements, X as the chalcogenide) have recently been attracting attention as thermoelectric materials. Possible magnetic enhancement of the thermoelectric properties has been proposed for electron-doped chalcopyrite CuFeS 2 which exhibits large power factors at room temperature. Promising ZT values close to 1 have been reported for TmAgTe 2 or YCuTe 2 due to very low thermal conductivities ( −1  K −1 at 800 K) resulting from a disordered sublattice of Cu atoms. To further explore the possibilities of the ABX 2 compounds, we study GdCu 1+x Te 2 which is a monoclinic layered compound that crystallizes in the C2/m space group, and has the f-electron Gd as a magnetic element, versus d-electron Fe in CuFeS 2 . Although the stoichiometric compound could not be stabilized, we report on the properties of this series of compounds sintered by spark plasma sintering (SPS). As for the other materials of ABX 2 type, compositions with x > 0.25 show very low thermal conductivities (0.64 W m −1  K −1 above 500 K for x = 0.25), which, together with a Seebeck coefficient above 0.2 mV K −1 , allows to reach a moderate ZT value near 0.2 at 540 K. We also discuss the dependence with the Cu excess content of the transport properties and the lack of effect of the magnetic moment of Gd on the Seebeck coefficient.