| Abstract |
| Ge-doped higher manganese silicides (HMSs) MnSi1.72-1.73:Gem (m = 0.01-0.04) were prepared and their thermoelectric properties were studied. HMS powders were synthesized by solid-state reaction of raw material powders (Mn, Si, and Ge) at 1273 K for 6 h in vacuum, and hot-pressed at 1173 K for 2 h under 70 MPa. Mn11Si19 or Mn15Si26 was the main HMS phase; only a small quantity of Si remained. The intermetallic compound MnSi was not produced. The lattice constants increased with the substitution of Ge at Si sites. With the increase in the Ge doping concentration, the electrical conductivity increased, while the Seebeck coefficient decreased. The power factor was significantly increased by the Ge doping, owing to the increase in the electrical conductivity. The Ge doping led to phonon scattering owing to the difference in mass between Ge and Si, leading to a reduced thermal conductivity. Therefore, the dimensionless figure of merit (ZT) was remarkably enhanced by the Ge doping. For MnSi1.72:Gem, the maximum ZT of 0.44 was obtained at 823 K for MnSi1.72:Ge0.01, while for MnSi1.73:Gem, the maximum ZT of 0.37 was achieved at 823 K for MnSi1.73:Ge0.03. |
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| Key Words |
| thermoelectric, HMS, higher manganese silicide, solid-state reaction, hot pressing |
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