ICT2014 Abstracts

Over the last years, an increasing number of studies were devoted to the identification of new efficient thermoelectric materials based on non-toxic and abundant elements. Sulfur-containing natural minerals such as sulfosalts belong to this class of materials. Tetrahedrites of general chemical formula (Ag,Cu,Fe)₁₂(Sb,As)₄S₁₃ were recently shown to exhibit interesting thermoelectric properties. The rather complex cubic lattice results in very low thermal conductivity values (0.3 – 0.4 W.m^-1.K^-1 at 300 K). Combined with high thermopower values, promising ZT values were reached in Cu_12-xZn_xSb₄S₁₃ (1.0 at 673 K for x = 0.5).

In this study, we tried to optimize the thermoelectric properties of Cu₁₂Sb₄S₁₃ viasubstitution of Te for Sb. The tetrahedrites Cu₁₂Sb_4-xTe_xS₁₃ (0 < x < 2) were synthesized by using a conventional powder-metallurgy route with either pure elements or precursors. Bulk materials were prepared in sealed quartz tube under inert atmosphere at 873 K. The resulting ingots were annealed at lower temperature, grounded into fine powders and densified by spark plasma sintering. The thermal stability was probed by temperature-dependent powder x-ray diffraction and differential scanning calorimetry.

The thermoelectric properties, including thermopower, electrical resistivity and thermal conductivity were investigated between 300 and 700 K. The thermal conductivity was found to be independent of the Te concentration remaining as low as 0.5 W.m^-1.K^-1. The electrical resistivity and thermopower increase with x, a result consistent with a gradual shift from a metallic state (x = 0.0) towards a semiconducting behavior (x = 2.0) and with electronic band structure calculations. A maximum ZT of 0.85 was obtained for x = 1.0 at 673 K.