Band degeneracy driven high power factor in higher manganese silicide for thermoelectric application

Abstract

Higher Manganese Silicide (HMS), a p-type semiconductor that obeys the 14-th electron rule, exhibits a high Seebeck coefficient and electrical conductivity attributed to the contribution of partially filled d-orbitals near the fermi level and high carrier mobility. However, its thermoelectric performance remains constrained by its high lattice thermal conductivity. To overcome this limitation, Cr and Sn were substituted in HMS in the nominal stoichiometries of Mn1-xCrxSi1.74-ySny (x = 0, 0.06, 0.08, y = 0.001). The Cr doping shifts the chemical potential toward the valence band edge, promoting metallic behavior that led to an enhanced electrical conductivity. Concurrently, the dislocation networks and grain boundary effects minimized the lattice thermal conductivity to ∼1.14 Wm−1K−1, yielding a peak ZT of ∼0.50 at 803 K in Mn0.92Cr0.08Si1.74. To further enhance the Seebeck coefficient, Sn co-doping has been carried out to explore the electronic structure by shifting the chemical potential toward the valence band, which results in enhanced Seebeck coefficient and electrical conductivity via carrier energy filtering. This co-doping approach results in a maximum power factor of ∼1154 μWm−1K−2 at 703 K in the Mn0.92Cr0.08Si1.739Sn0.001 sample, highlighting the synergistic role of Cr and Sn in tuning the carrier transport properties without severely compromising the thermal conductivity. These findings demonstrate that Cr and Sn co-doping serves as a viable approach to enhance the thermoelectric performance of HMS-based materials.