Akio Yamamoto

Thermoelectric properties of supersaturated Re solid solution of higher manganese silicides

In this study, we developed a higher manganese silicide (HMS) that possesses a high dimensionless figure of merit ZT exceeding unity. HMSs containing a larger amount of Re than its solubility limit were prepared by the liquid quenching technique, and the obtained metastable HMSs showed good thermal stability to enable pulse current sintering at 1240 K. The lattice thermal conductivity was effectively reduced with increasing Re concentration, whereas the electron transport properties were not greatly affected. Consequently, the ZT of p-type HMS increased to 1.04 at 6 at. % Re from 0.4 of the Re-free sample.

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

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.

The Potential of FeVSb Half-Heusler Phase for Practical Thermoelectric Material

The electronic structure and electron transport properties of FeVSb half-Heusler phase were calculated using first-principles calculations and Boltzmann transport equation. We found, as a result of theoretical calculations, that the magnitude of the dimensionless of figure of merit (ZT) could be increased up to ∼0.84 due to the drastic increase of the power factor when the carrier concentration of p-type FeVSb is optimized through element substitution to vary the valence electron concentration. We revealed that this large increase in ZT is closely related to the significant variations both in electronic density of states and spectral conductivity with decreasing energy at the top of the valence band.

Carrier concentration dependence of thermoelectric properties of Fe(V1− x ,Ti x )Sb half-Heusler phase

The thermoelectric properties of the FeV1− x Ti x Sb half-Heusler (HH) phase were studied in the temperature range from 300 to 700 K. All the samples prepared with the compositions of FeV1− x Ti x Sb (0 ≤ x ≤ 0.2) possessed a positive Seebeck coefficient, while the sample with x = 0 showed a negative sign. FeV0.80Ti0.20Sb exhibited a large positive Seebeck coefficient exceeding 300 µV K−1 and a low electrical resistivity below 2.00 ± 0.20 mΩ cm at 700 K, leading to a large power factor PF = 4.40 ± 0.50 × 10−3 W m−1 K−2. The thermal conductivity of FeV1− x Ti x Sb (x > 0) at 300 K decreased to less than half of that of the sample at x = 0, probably because the disordering caused by the Ti substitution enhanced the scattering probability of phonons. The consistency between measured and calculated properties indicates that FeV1− x Ti x Sb HH is suitable as a new practical thermoelectric material.