Enhancing thermoelectric performance of higher manganese silicide through Nb incorporation

Abstract Higher manganese silicide (HMS; MnSi 1.67–1.75 ) 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 (Mn 1‐ x Nb x Si 1.73 , 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 Mn 0.996 Nb 0.004 Si 1.73 , representing a 16% improvement over MnSi 1.73 (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 Mn 0.997 Nb 0.003 Si 1.73 , marking a 14% reduction relative to MnSi 1.73 (3.10 W m −1 K −1 ). The highest zT of 0.46 is realized in Mn 0.996 Nb 0.004 Si 1.73 at 773 K, marking a 15% increase over MnSi 1.73 ( 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.