Oxidation Behavior of Skutterudite-Based Thermoelectric Materials in High-Temperature Air Atmosphere

Power generation driven by thermoelectric conversion requires high chemical stability of the module under the practical operating conditions. The stability of the module in a high-temperature atmosphere depends on the constituent elements of the thermoelectric materials. This study systematically examines the oxidation behaviors of four skutterudite compounds (CoSb3, Co0.94Ni0.06Sb3, CeFe3CoSb12, and In0.25Co3FeSb12) under high-temperature atmospheric conditions using thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffraction, scanning electron microscopy (SEM), and energy dispersive x-ray spectroscopy (EDX). All four samples increase in weight at a certain temperature according to the TG curves, and several exothermic peaks are observed in the DTA curves, corresponding to the oxidation or decomposition of the thermoelectric materials. Various phases (e.g., CoSb2O4, Sb2O3, Sb2O4, and CoSb2O6 (or FeSbO4)) are formed after TG-DTA measurement up to 1073 K. The stable temperature ranges of the phases were similar in CoSb3 and Co0.94Ni0.06Sb3, and in CeFe3CoSb12 and In0.25Co3FeSb12. Notably, the temperature range in which the CoSb3-type phase is stable is significantly lower in CeFe3CoSb12 and In0.25Co3FeSb12 than in CoSb3 and Co0.94Ni0.06Sb3. SEM analysis after leaving the sintered materials in air at different temperatures for specified periods of time revealed the formation of several oxide layers on the surface.