Thermoelectric properties of Al–Mn–Si C40 phase containing small amount of W or Ta

Abstract

The lattice thermal conductivity of the Al–Mn–Si C40 phase was effectively reduced by substituting a small amount of W for Mn while maintaining a large Seebeck coefficient |S| > 100 µV/K and a low electrical resistivity ρ < 1.7 mΩ cm. The Al–Mn–Si-based C40 phase containing a small amount of W showed essentially the same behaviors of both Seebeck coefficient and electrical resistivity as those of a W-free sample at the same carrier concentration. This experimental result was consistent with the first principles calculations that predicted the absence of impurity states in the energy gap in association with the W atom at the Mn site. The lattice thermal conductivity, on the other hand, markedly decreased owing to the heavy element impurity scattering effect of phonons. Consequently, the ZT of the n-type Al27.5Mn29.0W3.0Fe1.0Si39.5 C40 phase increased to a value that was ∼4 times larger than that of the W-free sample.