Effects of Annealing on Microstructure and Thermoelectric Properties of Nanostructured CoSb3

Nanocrystallization of thermoelectric materials is an effective way to reduce their thermal conductivity, but so far the thermal stability of nanostructured thermoelectric materials has been little studied. Effects of annealing treatment on the microstructure and the thermoelectric properties of nanostructured CoSb₃ were investigated in this work. Samples with average grain size of 300 nm were prepared by spark plasma sintering of high-energy ball-milled nanosized CoSb₃ powders. The study shows that annealing has a very significant impact on the grain size of the samples. The grain size of the sample with 100 h annealing is three times greater than before annealing. The major phase in the 150-h-annealed sample is still skutterudite, except for a trace amount of Sb phase. With increasing annealing time, the density reduces slightly. In addition, the power factor of the sample decreases, thus resulting in a decrease of the thermoelectric figure of merit.