Oxidation Studies of Cu12Sb3.9Bi0.1S10Se3 Tetrahedrite

Tetrahedrites are widespread minerals with general formula Cu10M2Sb4S13 (M = Cu, Mn, Fe, Co, Ni, Zn). Their thermoelectric properties can be tuned through proper doping and reach zT values as high as 1, being considered promising low-cost thermoelectric materials. However, for practical application in thermoelectric devices, it is necessary to establish their ability to operate for long periods under working temperatures and atmospheres. We present herein studies of oxidation in air of Cu12Sb3.9Bi0.1S10Se3 tetrahedrite at four different temperatures between 230 degrees C and 375 degrees C, together with preliminary corrosion studies in aggressive NaCl electrolyte. Surface oxidation already occurs at the lower studied temperatures, but a strong decrease of the oxidation rate is observed for materials treated at intermediate temperature (275 degrees C), where a continuous surface layer of Cu2-xS forms, pointing to a protective effect of this layer that could be applied in devices operating at such temperatures. For the material treated at higher temperatures (350 degrees C and 375 degrees C), no tetrahedrite phases were seen after 1500 h, which can be related to the (tetrahedrite + chalcostibite + antimony -> skinnerite) reaction that occurs above 280 degrees C. Corrosion studies indicated that increasing the oxidation temperature unfortunately leads to a decrease of the corrosion resistance of tetrahedrite-based phases.