SnS及CrN热电材料第一性原理研究

发布时间：2018-03-24 06:15

本文选题：第一性原理计算　切入点：热电材料　出处：《电子科技大学》2017年硕士论文

【摘要】：热电材料是指一类能够将热能转化为电能的材料体系,广泛应用于便携式电子产品、航空航天及国防军事等领域。但是,目前商品化的热电材料主要是锑化铋,由于其具有较大的毒性,副反应较多,成本较高,热电优值不高等缺点,限制了它的广泛应用。因此研究和开发新型具有优异热电性质的材料体系成为当务之急。随着现代科学技术的进步以及量子力学这门学科的不断发展,模拟计算在材料的研究设计中起到越来越关键的作用。通过对材料原子尺度的计算,我们可以准确的预测材料的一些性能和解释实验中出现的现象,进而为实验探究提供理论依据。本文基于第一性原理,对两种潜在的新型热电材料硫化亚锡(SnS)及氮化铬(CrN)进行了研究,重点分析了两种材料的能带结构(Energy band structure)和态密度结构(Density of states)。结果表明,硫化亚锡是一种间隙能隙半导体,能隙宽度为Eg=0.733eV,同时也表明它可以在较高温度下获得更好的热电性能,这与现有的实验结果相吻合。并且通过在500K与700K时对硫化亚锡的运输性质进行研究,我们发现其在700K时具有更大的功率因子,与之前的能带结构分析结果相对应。除此之外,通过分析塞贝克系数、电导率和功率因子随费米能级的变化情况,表明对硫化亚锡材料体系而言p型掺杂要优于n型掺杂。在此基础上,我们选择了Na、Mg、Al、Si、Ge、Pb六种元素对其进行掺杂,通过形成能结算证明可以存在掺杂稳定结构,并分析了掺杂后的能带结构与态密度结构图,发现Al与Pb掺杂后较有可能得到较高的塞贝克系数和电导率,进而得到具有较高热电优值的热电材料。另一个材料体系氮化铬费米面位于价带中,呈现金属特性,具有较高的电导率。通过计入自旋极化与不计入自旋极化两种计算方式,初步分析了其塞贝克系数与电导率变化情况,发现在两种条件下塞贝克系数相差不大,但是计入自旋极化后材料的电导率明显提升,因而可能具有更高的功率因子。我们通过上述理论计算可以初步揭示材料的微观电子结构,并根据计算所得的能带结构与态密度结构图分析材料的半导体性质,最终由塞贝克系数、电导率与功率因子预测材料的热电性质,对后续实验提供指导作用。
[Abstract]:Thermoelectric material is a kind of material system which can convert heat energy into electric energy. It is widely used in portable electronic products, aerospace, national defense and military, etc. However, the thermoelectric materials are mainly bismuth antimonide. Because of its great toxicity, more side effects, high cost, low thermoelectric value and so on, Therefore, it is urgent to study and develop new material systems with excellent thermoelectric properties. With the progress of modern science and technology and the continuous development of quantum mechanics, Simulation calculation plays a more and more important role in the research and design of materials. By calculating the atomic scale of materials, we can accurately predict some properties of materials and explain the phenomena in experiments. Based on the first principle, two potential new thermoelectric materials, tin sulphide SNS and chromium nitride CrNs, are studied in this paper. The energy band structure (band structure) and density of state structure (Density of states) of the two materials are analyzed in detail. The results show that tin sulfide is a gap energy gap semiconductor with a gap width of 0.733 EV. It also shows that it can obtain better thermoelectric properties at higher temperature. By studying the transport properties of stannous sulfide at 500K and 700K, we find that it has a larger power factor at 700K, which corresponds to the previous energy band structure analysis results. By analyzing the variation of Seebeck coefficient, conductivity and power factor with Fermi energy level, it is shown that p-type doping is better than n-type doping for tin sulfide system. It is proved that there is a stable doping structure through the formation energy settlement. The energy band structure and the density of state structure diagram after doping are analyzed. It is found that the higher Seebeck coefficient and conductivity can be obtained after Al and Pb doping. Then the thermoelectric material with high thermoelectric value is obtained. The chromium Fermi nitride surface of another material system is located in the valence band, which shows the metal characteristic and has high conductivity. By taking into account the spin polarization and excluding the spin polarization, two calculation methods, the spin polarization and the non-spin polarization, are taken into account. The variation of Seebeck coefficient and conductivity is analyzed preliminarily. It is found that there is no difference between Seebeck coefficient and conductivity under the two conditions, but the conductivity of the material with spin polarization is obviously increased. The microelectronic structure of the material can be preliminarily revealed by the theoretical calculation, and the semiconductor properties of the material can be analyzed according to the calculated energy band structure and the density of state structure diagram. Finally, the thermoelectric properties of the material are predicted by Seebeck coefficient, conductivity and power factor.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TB34

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