Thermoelectric property of fine-grained CoSb₃ skutterudite compound fabricated by mechanical alloying and spark plasma sintering

Skutterudite CoSb₃ polycrystalline materials were prepared using a combined process of mechanical alloying (MA) and spark plasma sintering (SPS). The influence of SPS temperature on the thermoelectric properties was focused in this work with a special emphasis on the analysis of the size effects of grains. The average grain sizes decreased from 300 to 50 nm with decreasing SPS temperatures from 600 to 300 °C. The electrical resistivities of samples spark plasma sintered at 300-600°C all decreased with increasing temperature, indicating a classic intrinsic conduction behaviour of semiconductors. The samples spark plasma sintered at 300-500°C showed a positive Seebeck coefficient while the sample spark plasma sintered at 600°C showed a negative Seebeck coefficient. The room-temperature thermal conductivities were reduced from 4.30 to 2.92 W m^-1 K^-1 as the grain sizes were decreased from 300 to 100 nm corresponding to SPS at 600 and 400 °C, respectively. The present work indicates that MA and SPS is a good combination for fabricating fine-grained CoSb₃ thermoelectric materials.