Preparation Of Mnsi_1.7 Thermoelectric Material And Calculations Of Its Electronic Structure

Thermoelectric materials are semiconductor functional materials which can directly convert heat into electricity and vice versa. Higher manganese silicides MnSi1.7 are very promising among them. MnSiu has broad application prospects because of its high chemical stability, good oxidation resistance, non-toxic pollution and low cost.In the present work, MnSiu bulk thermoelectric materials were prepared by powder metallurgy. The influences of the process parameters on the quality of samples were investigated. Based on the results, a reasonable process was obtained. The variation of electrical conductivity with temperature was also investigated. Meanwhile, the band structure and density of states of Mn4Si7 were calculated theoretically.A mixture of Mn powder and Si powder was wet-milled with ethanol, and then pressed under a pressure of 486 MPa. Then MnSiu bulks with high density were obtained. As the increase of the sintering temperature and sintering time, the proportion of MnSiu in the samples were gradually increased. Faster cooling rate promotes the reservation of MnSiu to temperature. The conductivity of MnSiu samples increased with temperature, and then decreased, with a minimum at about 400°C.The thermoelectric properties of thermoelectric materials are closely related to their electronic structure. Study of electronic structure of the thermoelectric materials can provide theoretical guidance to develop high-performance thermoelectric materials. By means of first principles calculations based on density functional theory, the band structure and density of states of Mn4Si7? were investigated. The results indict that Mn4Si7 has a direct band gap of 0.82 eV. Si vacancy in Mn4Si7?crystal produces an impurity state near the Fermi level, leading to the formation of p-type Mn4Si7.Si vacancy introduced increases the density of states near the Fermi level, which indicates that the introduction of the defects may improve the ZT factor of Mn4Si7.