Thermoelectric Performance of Cr Doped and Cr–Fe Double-Doped Higher Manganese Silicides with Adjusted Carrier Concentration and Significant Electron–Phonon Interaction

Polycrystalline higher manganese silicides Mn1–xCrxSi1.74 (x = 0, 0.10, 0.20) with Cr single doping and Mn1–2yCryFeySi1.74 (y = 0.10, 0.20) with Cr–Fe double doping have been prepared by arc melting and spark plasma sintering. Hall effect results and thermoelectric transport properties measurements demonstrate that Cr doping effectively increases the carrier concentration, thereby giving rise to enhanced electrical conductivity and power factor. Coupled with an enlarged effective mass and a reduction in the lattice thermal conductivity, a maximum zT is realized in Mn0.90Cr0.10Si1.74. It is also proved that the carrier concentration and carrier scattering mechanism could be altered through further doping on the Mn site by Fe, which leads to a lower electrical conductivity and higher Seebeck coefficient. Factors related to the suppression of the lattice thermal conductivity, like mass and strain field fluctuation scattering and electron–phonon scattering, are also analyzed. This work reveals the effects of Cr single doping and Cr–Fe dual-element doping on the carrier concentration, carrier scattering mechanism, and lattice thermal conductivity of higher manganese silicides.