“Pesting”-like oxidation phenomenon of p-type filled skutterudite Ce0.9Fe3CoSb12

Oxidation behavior of p-type filled skutterudite Ce0.9Fe3CoSb12 in air was investigated and the oxidation mechanism was discussed in this study. Ce0.9Fe3CoSb12 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 Ce0.9Fe3CoSb12 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 Ce0.9Fe3CoSb12 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 MyFe4−xCoxSb12-based skutterudite thermoelectric device.