本文選題：第一性原理計算　切入點：熱電材料　出處：《電子科技大學(xué)》2017年碩士論文

【摘要】：熱電材料是指一類能夠?qū)崮苻D(zhuǎn)化為電能的材料體系,廣泛應(yīng)用于便攜式電子產(chǎn)品、航空航天及國防軍事等領(lǐng)域。但是,目前商品化的熱電材料主要是銻化鉍,由于其具有較大的毒性,副反應(yīng)較多,成本較高,熱電優(yōu)值不高等缺點,限制了它的廣泛應(yīng)用。因此研究和開發(fā)新型具有優(yōu)異熱電性質(zhì)的材料體系成為當(dāng)務(wù)之急。隨著現(xiàn)代科學(xué)技術(shù)的進(jìn)步以及量子力學(xué)這門學(xué)科的不斷發(fā)展,模擬計算在材料的研究設(shè)計中起到越來越關(guān)鍵的作用。通過對材料原子尺度的計算,我們可以準(zhǔn)確的預(yù)測材料的一些性能和解釋實驗中出現(xiàn)的現(xiàn)象,進(jìn)而為實驗探究提供理論依據(jù)。本文基于第一性原理,對兩種潛在的新型熱電材料硫化亞錫(SnS)及氮化鉻(CrN)進(jìn)行了研究,重點分析了兩種材料的能帶結(jié)構(gòu)(Energy band structure)和態(tài)密度結(jié)構(gòu)(Density of states)。結(jié)果表明,硫化亞錫是一種間隙能隙半導(dǎo)體,能隙寬度為Eg=0.733eV,同時也表明它可以在較高溫度下獲得更好的熱電性能,這與現(xiàn)有的實驗結(jié)果相吻合。并且通過在500K與700K時對硫化亞錫的運輸性質(zhì)進(jìn)行研究,我們發(fā)現(xiàn)其在700K時具有更大的功率因子,與之前的能帶結(jié)構(gòu)分析結(jié)果相對應(yīng)。除此之外,通過分析塞貝克系數(shù)、電導(dǎo)率和功率因子隨費米能級的變化情況,表明對硫化亞錫材料體系而言p型摻雜要優(yōu)于n型摻雜。在此基礎(chǔ)上,我們選擇了Na、Mg、Al、Si、Ge、Pb六種元素對其進(jìn)行摻雜,通過形成能結(jié)算證明可以存在摻雜穩(wěn)定結(jié)構(gòu),并分析了摻雜后的能帶結(jié)構(gòu)與態(tài)密度結(jié)構(gòu)圖,發(fā)現(xiàn)Al與Pb摻雜后較有可能得到較高的塞貝克系數(shù)和電導(dǎo)率,進(jìn)而得到具有較高熱電優(yōu)值的熱電材料。另一個材料體系氮化鉻費米面位于價帶中,呈現(xiàn)金屬特性,具有較高的電導(dǎo)率。通過計入自旋極化與不計入自旋極化兩種計算方式,初步分析了其塞貝克系數(shù)與電導(dǎo)率變化情況,發(fā)現(xiàn)在兩種條件下塞貝克系數(shù)相差不大,但是計入自旋極化后材料的電導(dǎo)率明顯提升,因而可能具有更高的功率因子。我們通過上述理論計算可以初步揭示材料的微觀電子結(jié)構(gòu),并根據(jù)計算所得的能帶結(jié)構(gòu)與態(tài)密度結(jié)構(gòu)圖分析材料的半導(dǎo)體性質(zhì),最終由塞貝克系數(shù)、電導(dǎo)率與功率因子預(yù)測材料的熱電性質(zhì),對后續(xù)實驗提供指導(dǎo)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.
【學(xué)位授予單位】：電子科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TB34

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本文編號：1657065