Oxidation Behavior of Microstructured and Nanostructured Co0.94Ni0.06Sb3 Thermoelectric Materials

The skutterudite materials such as of Co0.94Ni0.06Sb3 are widely studied for their thermoelectrical properties, i.e., their ability to produce electricity from heat. They are generally employed under vacuum but their use under oxidative environments (e.g., in air) is currently becoming an attractive perspective for power generation and a major challenge for research. The nanostructuring of the skutterudite materials is known to be an efficient solution to enhance their thermoelectric properties but the corresponding impact on the oxidation behavior of the material is still not really explored. For that purpose, this work aims at studying the oxidation behavior of microstructured Co0.94Ni0.06Sb3 and nanostructured Co0.94Ni0.06Sb3 under a flow of air at 800 K for 15 h, 100 h and 1000 h. The formation of a surface oxide layer is observed for both samples. The results show that the surface layer is a mixture of several oxide phases in various amounts depending on the oxidation time and on the structuring scale of the material. Moreover, the nanostructured skutterudite material is less affected by oxidation than the microstructured one. Indeed, the nanostructuring promotes the formation of the spinel oxide CoSb2O4/CoO·Sb2O3 that provides a long-term oxidation protection to the skutterudite material. Consequently, Co0.94Ni0.06Sb3 is established to be a promising thermoelectric material usable under oxidative environments, particularly being nanostructured.