Synthesis and thermoelectric properties of nano/micro-meter CoSb3-based bulks processed by in-situ spark plasma sintering

Nanostructure materials exhibit different properties from those of corresponding bulk substances, the decrease in the grain size of the material leads to a drastic increase in the density of grain boundaries, which brings out a significant reduction in thermal conductivity, kappa, and so improve the value of thermoelectric figure-of-merit, ZT. But the decreased grain size reduces the electrical conductivity and Seebeck coefficient at the same time. Based on the above reasons, a novel method of in-situ spark plasma sintering (SPS) is used to synthesize CoSb₃-based Skutterudite compounds with nano/micro-meter grains by controlling the grain size of raw materials, and the thermoelectric properties are studied systematically. The results indicate that, the ratio of electrical conductivity and thermal conductivity is optimized, and a relative high Seebeck coefficient is obtained at nano/micro-meter scale. As a result, the dimensionless figure of merit ZT is greatly improved for CoSb₃, and La_0.3FeCo₃Sb₁₂, the highest value of ZT of 0.34 and 0.72 is obtained at 700 K for CoSb₃ and La_0.3FeCo₃Sb₁₂ Skutterudite compound, respectively