Enhancing thermoelectric performance of higher manganese silicide through Nb incorporation
摘要
Higher manganese silicide (HMS; MnSi1.67–1.75) is a promising thermoelectric (TE) material due to its eco-benign composition, low price, and mechanical/thermal stability. However, its high thermal conductivity caps its intrinsic zT at ~ 0.38, despite an impressive power factor. Herein, bulk HMS (Mn1-xNbxSi1.73, x = 0, 0.003, 0.004, and 0.005) samples were synthesized via levitation melting. Benefiting from element doping, which hinders high-frequency phonon movement, and from secondary-phase engineering, which suppresses low-frequency phonon transport and filter out low-energy carrier, Nb-incorporated samples exhibit both a high power factor and a low thermal conductivity relative to Nb-free sample. The highest power factor of 1.70 mW m−1 K−2 at 723 K is achieved in Mn0.996Nb0.004Si1.73, representing a 16% improvement over MnSi1.73 (1.46 mW m−1 K−2 at 773 K). At 823 K, the lowest thermal conductivity (2.67 W m−1 K−1) is achieved in Mn0.997Nb0.003Si1.73, marking a 14% reduction relative to MnSi1.73 (3.10 W m−1 K−1). The highest zT of 0.46 is realized in Mn0.996Nb0.004Si1.73 at 773 K, marking a 15% increase over MnSi1.73 (zT ≈ 0.40). The as-synthesized samples also exhibit robust mechanical properties, sufficient for the device fabrication. These results underscore the synergistic effect of alloying and second-phase engineering to enhance the TE performance of HMS and provide guidance for future research.
Graphical Abstract