Effects of sintering temperature on microstructure and thermoelectric properties of Ce-filled Fe₄Sb₁₂ skutterudites

The improvement of thermoelectric properties of p-type iron-based skutterudites is limited due to the present of more iron-rich impurity phases induced by the inherent structural instability of Fe-containing skutterudites. How to reduce the content of the impurity phase in p-type Fe-based skutterudites is a key to obtain high ZT value. Ce_1.25Fe₄Sb₁₂ materials with different sintering temperatures (723 K, 773 K, 798 K, 823 K and 848 K) have been prepared by a traditional melting-quenching-annealing process coupled with spark plasma sintering (SPS) technique. The results of XRD and EPMA analysis indicate that all the SPSed samples consist of the main skutterudite phase and impurity phases of FeSb₂, Sb, CeSb₂ and oxides of Ce and Sb. Compared with other SPSed samples, the SPS-773 K sample has the best thermoelectric properties due to the relatively fewer impurity phases, a large number of micro-nanoscale particles at the grain boundary and more voids. The SPS-773 K sample shows the largest ZT value over the entire test temperature range due to the higher power factor and lower lattice thermal conductivity. The maximum ZT value reaches 0.81 at 800 K. This indicates that thermoelectric properties of Ce-filled Fe₄Sb₁₂ skutterudite materials can be effectively improved by reducing impurity phases induced by the optimization of the sintering temperature.