Enhancing thermoelectric performance of higher manganese silicide through Ge doping

Higher manganese silicide (HMS, or MnSi x , with x ranging from 1.67 to 1.75) is a promising medium-temperature TE material due to its competitive thermoelectric and mechanical properties. In this work, samples with a nominal composition of Mn(Si 1- x Ge x ) 1.73 ( x = 0, 0.007, 0.008, 0.009, and 0.010) were prepared by combining vacuum levitation melting with spark plasma sintering . The highest PF of 1.15 mW m −1 K −2 , achieved at 723 K for the x = 0.008 sample, is 19 % higher than that of pristine HMS ( PF ≈ 0.96 mW m −1 K −2 ). The lowest thermal conductivity is reduced by 19.55 %, from 3.12 W m −1 K −1 (pristine HMS) to 2.51 W m −1 K −1 (the x = 0.008 sample) at 823 K. Doping with Ge successfully decoupled the interdependent electronic and thermal transport properties, leading to a 47 % increase in zT from 0.23 for the pristine HMS to 0.34 for the x = 0.008 sample. • Valence electron count derived from modulation vector. • Fermi level tuned by Ge doping. • Suppression of intrinsic excitation.