Effects of Cobalt Substitution on Crystal Structure and Thermoelectric Properties of Melt-Grown Higher Manganese Silicides
To improve the thermoelectric (TE) properties of melt-grown higher manganese silicides MnSiγ, dissipation of MnSi precipitates that deteriorate the electrical conductivity is required. We have investigated the effects of light cobalt (Co) substitution on TE properties and MnSi precipitates of MnSiγ. A 4% substitution of Mn with Co is an effective approach to eliminate MnSi precipitates from melt-grown MnSiγ, which is confirmed by powder x-ray diffraction and energy-dispersive spectroscopy measurements. Furthermore, this light Co substitution leads to increase of the hole carrier concentration, resulting in a great increase in the electrical conductivity from 24 × 103 S/m to 54 × 103 S/m at 700 K. The resulting power factor exhibits 1.9 × 10−3 W/mK2 around 700 K. Moreover, the lattice thermal conductivity is greatly decreased by partial Co substitution compared with that of Co-free MnSiγ. Consequently, the dimensionless figure-of-merit zT of (Mn1−xCox)Siγ samples increases from 0.27 for x = 0 to 0.50 for x = 0.04 in the vicinity of 800 K.
KeywordsHigher manganese silicides valence electron counts thermoelectric properties MnSi precipitate cobalt substitution
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