ICT2014 Abstracts

        MnSi_γ is known to possess a large magnitude of Seebeck coefficient, metallic electrical conductivity, and relatively small thermal conductivity. These characteristics definitely lead to a relatively large value of dimensionless figure of merit ZT > 0.4. These rather good thermoelectric properties are partly attributed to its electronic structure; a large peak in density of states and several overlapping bands both observable near the edge of valence band.  The rather complicated crystal structure, on the other hand, provides us with the relatively small lattice thermal conductivity.

         The power factor of MnSi_γ is almost comparable with that of practical thermoelectric materials, such as Bi₂Te₃, but its lattice thermal conductivity is slightly larger. It is, therefore, naturally considered that if the lattice thermal conductivity is slightly reduced, MnSi_γ would be one of the most plausible thermoelectric materials consisting solely of cheap, environmentally friendly elements.

        In this study, we employed partially substitution of W for Mn in MnSi_γ to effectively reduce its lattice thermal conductivity. We speculated that electronic structure and electron transport properties are less sensitive to the W-substitution, because such tendency was confirmed in Al-Mn-Si C54-phase and C40- phase both of which possess the similar local atomic arrangement about Mn as that in MnSi_γ. Unfortunately, however, the solubility limit of W in MnSi_γ was negligibly small. For increasing W concentration in MnSi_γ, we used single-role liquid quenching technique.

         By using the liquid quenching technique, we succeeded in obtaining MnSi_γ-type structure containing 3 at.% W without precipitation of secondary phase. The magnitude of Seebeck coefficient was almost unchanged with W-substitution for Mn, while the lattice thermal conductivity was effectively reduced. As a result, we succeed in effectively increasing the magnitude of ZT. The thermoelectric properties of the prepared samples together with their thermal stability will be explained in detail at the presentation.