Unique surface structure resulting in the excellent long-term thermal stability of Fe4Sb12-based filled skutterudites

Abstract

The evolutions of the phase composition, microstructure, and thermoelectric properties of BaFe4Sb12 materials at 773 K in vacuum were investigated to evaluate their long-term thermal stabilities. It was observed that the interior of the BaFe4Sb12 exhibited excellent thermal stability, while the surface decomposed into FeSb2, Sb, and Ba5Sb3. However, the decomposition rate sharply declined with increasing annealing time, and the thicknesses of the decomposition layer was approximately 49 μm after annealing for 30 days. Thermoelectric performances negligibly changed during the annealing process, and the dimensionless figure of merit remained in the range of 0.61 ± 0.02 at 800 K. The unique decomposition layer, wherein Ba5Sb3 compounds enriched in the outermost layer and along the FeSb2 grain boundaries, served as a dense protective cover to effectively retard the Sb sublimation, resulting in excellent long-term thermal stability. This work provides a plausible explanation for the long-term thermal stability of Fe4Sb12-based filled skutterudites.