Preparing filled CoSb3 skutterudites at 500 °C by a self-reduction sol–gel route

Abstract

In this study, CoSb₃ and Ba filled CoSb₃ skutterudites are synthesized by a convenient self-reduction sol–gel method using a mixed-acid (citric acid & oxalic acid) as a coordination and reduction agent at 500 °C in N₂. The influence of the mixed-acid ratio and the heat treatment conditions on the sample phases is discussed. The results show that single phase Ba_xCoSb₃ (0 ≤ x ≤ 0.15) are synthesized successfully at 500 °C for 30 min in N₂, and a ratio from 3 : 1 to 5 : 1 for citric acid/oxalic acid is necessary. The reaction mechanism can be described as the citric acid coordinating well with Co²⁺ and Sb³⁺ and producing a stable gel, while oxalic acid plays a role in tight binding and fully reducing particles in the reaction system. Furthermore, the maximal filling fraction of Ba filled CoSb₃ is 0.15 in this sol–gel method, which is slightly higher than that of Ba_0.51Co₄Sb₁₂ synthesized by the high pressure synthesis method.