【作者】 杨文昭；

【导师】 师春生；

【作者基本信息】 天津大学 ， 材料学， 2010， 硕士

【摘要】 热电材料是实现热能和电能之间相互转换的一种半导体功能材料。其中较有前景的是高锰硅化物MnSi_1.7。它具有化学稳定性高、抗氧化性能好、无毒无污染、成本低等优点,具有广泛的应用前景。本文采用粉末冶金法制备了MnSi_1.7块体热电材料。通过对比不同工艺参数对试样的影响,得到合理的制备工艺参数,并考察其电导率随温度的变化规律。同时,为了深入理解MnSi_1.7的电子结构,对Mn₄Si₇的能带结构和态密度进行了较为完备的理论计算和分析。采用酒精湿磨方法将Mn粉和Si粉混合后,压制压力为486 MPa条件下制备出的MnSi_1.7块体材料成型性和致密性最佳。随着烧结温度的升高和烧结时间的延长,产物中MnSi_1.7所占比例逐渐升高。较快的降温速率对MnSi_1.7相的保留有很好的促进作用。MnSi_1.7块体材料的电导率随着温度的升高,先增大后减小,在400℃左右时达到了最小值。热电材料的热电性能与其电子结构密切相关,研究其电子结构可为开发高性能热电材料提供理论指导。本文利用基于密度泛函理论的第一性原理对Mn₄Si₇的能带结构和态密度做了较为完备的理论计算和分析,计算结果表明,Mn₄Si₇具有0.82 eV的直接能隙。体系中Si空位的引入导致在费米能级附近产生杂质态,形成p型Mn₄Si₇;Si空位的存在使得费米能级附近态密度的增加,这预示通过在Mn₄Si₇中引入缺陷可能提高其ZT系数。更多还原

【Abstract】 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.更多还原