"Pesting"-like oxidation phenomenon of p-type filled skutterudite Ce_0.9Fe₃CoSb₁₂

Highlights: • Ce_0.9Fe₃Co₁Sb₁₂ exhibits "pesting"-like oxidation phenomenon at high temperature. • The highest oxidation rate of Ce_0.9Fe₃Co₁Sb₁₂ appears around 800 K. • Severe periodically oxide layer peeling-off behavior is observed around 800 K. • The co-existence of Fe and Co is responsible for the poor oxidation resistance. - Abstract: Oxidation behavior of p-type filled skutterudite Ce_0.9Fe₃CoSb₁₂ in air was investigated and the oxidation mechanism was discussed in this study. Ce_0.9Fe₃CoSb₁₂ exhibits interesting "pesting"-like oxidation phenomenon around 800 K. The bulk sample completely disintegrates into a crowd of plate-like particles under this temperature range after only 24 h exposure in air. However, this abnormal oxidation phenomenon is not observed at temperature below 750 K or above 850 K. This result is consistent with the thermogravimetry and derivative thermogravimetry measurements which show that the oxidation rate for Ce_0.9Fe₃CoSb₁₂ around 800 K is the highest among 650–900 K. Microstructure observations suggest that this "pesting"-like oxidation is related with the severe periodically oxide layer peeling-off behavior around 800 K, which makes the Ce_0.9Fe₃CoSb₁₂ samples are easy to be oxidized because the fresh substrate surface is always exposed to high concentration oxygen atmosphere. X-ray diffraction and X-ray photoelectron spectroscopy measurements indicated that in the oxide scale the direct contact of Fe³⁺-oxide and CoSb₂O₄ which possess different formation/growth rate and volume expansion coefficient should be responsible for this peculiar oxide layer peeling-off behavior around 800 K. This work can serve as an important reference for the designation of M_yFe_4−xCo_xSb₁₂-based skutterudite thermoelectric device