Effects of sintering temperature on the microstructure and thermoelectric properties of mesostructured Co₄Sb_11.5Te_0.5 skutterudites dispersed nano-TiN

The mesostructured skutterudites Co₄Sb_11.5Te_0.5 + nano-TiN composites are prepared through ball milling and spark plasma sintering (SPS). The influence of the various SPS temperatures within the range of 813–933 K on the microstructure and thermoelectric properties are focus in this work. The average grain sizes of the skutterudites increase from ~ 110 to ~ 500 nm with the increasing SPS temperature, while the densities of composites decrease from 7.02 to 6.26 g cm⁻³. Additionally, the phase of CoTe₂ is detected in the samples sintered at 903–933 K. With the SPS temperature increasing from 813 to 903 K, the electrical conductivity and thermal conductivity increase simultaneously, and then decrease when SPS temperature rises to 933 K. The absolute value of Seebeck coefficient shows no clear changes when SPS temperature is not higher than 873 K but then slightly decreases with the increasing of SPS temperature. At last, the optimum SPS temperature is determined as 873 K, the ZT value of 1.07 at 800 K for the sample SPSed at 873 K is obtained, which is 11.5% higher than that of the sample SPSed at 903 K.