Enhanced thermoelectric properties in chimney ladder structured Mn(B_xSi_(1-x))_(1.75) due to the dual lattice occupation of boron

摘要

Due to its abundant, inexpensive, and nontoxic features, higher manganese silicide MnSi1.75 has drawn intensive attention as a promising middle temperature thermoelectric material. In this study, we applied aberration-corrected scanning transmission electron microscopy to characterize its chimney ladder crystal structure and found the particular contrast along the [110] direction, contributed from the enhancement of helical Si layers on Mn layers. Moreover, it is demonstrated that the Seebeck coefficient and electrical conductivity of MnSi1.75 could be simultaneously reinforced via boron doping, giving a peak power factor value of 1.72 mW m(-1) K-2 at 723 K for Mn(B0.04Si0.96)(1.75). Interestingly, it is indicated that boron would occupy both Si lattice and interstitial sites, resulting in an optimized charge carrier concentration and a reduced lattice thermal conductivity at the same time. A maximum zT value of similar to 0.55 at 773 K and a high zT(ave) value of 0.4 from 300 to 823 K were eventually realized in the Mn(B0.04Si0.96)(1.75) sample.