Nanostructured CoSi Obtained by Spark Plasma Sintering
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Cobalt monosilicide is a cheap, environmentally friendly thermoelectric material for medium temperatures (200â€“700Â°C). While its power factor is similar to the state-of-the-art thermoelectric materials, its thermal conductivity is too large to reach high ZT values. Nanostructuring might be an interesting strategy to reduce the phonon mean free path thereby improving the thermoelectric performance. In this paper, we report on a 35% reduction of the thermal conductivity of n-type CoSi by a nanostructuring approach. CoSi nanostructured powders were synthesized by arc melting, followed by 4Â h mechanical milling. By optimizing the spark plasma sintering thermal and pressure cycle, pellets with 5â€“10% porosity were obtained. During sintering, a small amount of Co2Si extra phase appeared and grains coarsened. After sintering, the pellets remained nanostructured, with an averaged grain size of 70Â nm. The reduction of thermal conductivity is ascribed to a decrease in both the electronic and lattice contributions. The former is directly related to a decrease in the electrical conductivity, which appears to be the limiting factor preventing nanostructured CoSi from reaching enhanced thermoelectric performances.
KeywordsNanostructuring thermoelectricity Seebeck spark plasma sintering (SPS) thermal conductivity cobalt silicide
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