High-Temperature Oxidation Behavior of Filled Skutterudites YbyCo4Sb12

The oxidation behavior of filled skutterudites Yb (y) Co4Sb12 was investigated. The overall oxidation of Yb (y) Co4Sb12 consists of two stages. In the first stage, densified oxide layers form on the surface gradually due to the reaction between oxygen and skutterudite at high temperature. In the second stage, microcracks evolve in the oxide layers because of mismatch of coefficient of thermal expansion between the oxide layer and skutterudite matrix, which accelerates the oxidation by providing transport paths for both outside oxygen and inside Sb. The overall oxidation process can be described through the repetitive cycle: dense layer formation -> stress release -> microcrack formation -> self-repair -> dense layer formation. The oxidation activation energy of filled skutterudites determined using thermogravimetry method with multi-heating rates is lower than that of unfilled CoSb3. Moreover, it was found that, with increasing Yb filling fraction, the oxidation activation energy decreases monotonically. Our results suggest that protection against oxidation is necessary for application of filled skutterudites.