Production of (Fe,Co)Si2 and (Fe.Mn)Si2 Thermoelectric Materials by Spark Plasma Sintering

In this study, FeSi2 bulk specimens were prepared by mechanical alloying, spark plasma sintering, and subsequent annealing. The annealed FeSi2 bulk specimens consisted of the β-FeSi2 phase and exhibited high Seebeck coefficient values. The maximum Seebeck coefficient of 356 μVK−1 was achieved in the FeSi2 bulk specimen annealed at 1173 K for 6 h. However, the power factor of the FeSi2 bulk specimen was quite small due to its high electrical resistivity, and a drastic improvement is required. Therefore, Mn- and Co-substituted specimens, Fe1−xMnxSi2 (x = 0.2–0.8) and Fe1−xCoxSi2 (x = 0.2–0.8), were produced, and their thermoelectric properties were evaluated. The Mn- and Co-substituted specimens exhibited lower electrical resistivity and a higher power factor than the FeSi2 bulk specimen. The Fe1−xMnxSi2 (x = 0.2–0.8) bulk specimens were p-type thermoelectric materials, and a Seebeck coefficient of 262 μVK−1 and a power factor of 339 μWm−1K−2 were achieved in the Fe0.94Mn0.06Si2 bulk specimen. On the other hand, the Fe1−xCoxSi2 (x = 0.2–0.8) bulk specimens were n-type thermoelectric materials, and a Seebeck coefficient of −180 μVK−1 and a power factor of 667 μWm−1K−2 were achieved in the Fe0.96Co0.04Si2 bulk specimen.