臺灣博碩士論文加值系統

碲化鉍是目前研究已經成熟且廣泛應用的常溫熱電材料，本論文採用非平衡分子動力學(NEMD)方法來研究雙晶界結構對碲化鉍材料熱傳性質的影響。模擬中，採用Huang和Kaviany所提出的勢能函數進行模擬，此勢能函數兼具二體與三體勢能及庫倫勢能。
在單晶碲化鉍的模擬中，先以平衡分子動力學(EMD)方法計算原子徑向分佈函數、聲子態密度及色散關係用來確認初始結構及勢能函數的選擇設置是否正確，接著以非均質非平衡分子動力學方法，配合控制熱流量法，進行熱傳導係數的計算。模擬得到的熱傳導係數在定性上與實驗量測值有一致的溫度相依性，定量上則略高於實驗量測值。
在雙晶界碲化鉍的模擬中，本論文分別對三種不同種類的雙晶界碲化鉍進行熱傳導係數及界面熱阻的計算。熱傳導係數的模擬結果顯示，材料中的雙晶界會破壞長波長聲子，使熱傳導係數下降。其中Te1層雙晶界結構最為穩定，故界面熱阻最小；反之，Te2層雙晶界界面熱阻最大。此外，縮短雙晶界的距離可以提高界面熱阻。整體來說，在室溫下，單一雙晶界結構碲化鉍等效熱傳導係數較單晶碲化鉍降低約15%，此與實驗上的觀察是一致的。

Bismuth Telluride (Bi2Te3) is the best thermoelectric material at room temperature. This research applies the equilibrium molecular dynamics (EMD) and the non-equilibrium molecular dynamics (NEMD) simulation methods to investigate the effect of twin boundaries on the phonon properties of Bi2Te3.The potential function suggested by Huang and Kaviany in 2008 is adopted, including the two-body and three-body interactions as well as the Columbic force.
From the EMD simulation results of single crystal Bi2Te3, the radial distribution function, the phonon density of state and the phonon dispersion relation are calculated. The agreement of the calculation results with literature confirms the accuracy of the initial conditions and the appropriateness of the employed potential function. The NEMD simulation results with a controlled heat flux on the other hand provide a calculation of the lattice thermal conductivity. The computed thermal conductivity qualitatively agrees with the experimental measurements, but slightly larger quantitatively.
The simulation results of twinned Bi2Te3 show that twin boundary structure can interfere long mean-free-path phonons and consequently reduce the lattice thermal conductivity. It is also noticed that the interfacial energy and stability of the simulated system differ when the twin boundary occurs at different atomic layers. The Te1-twin boundary structure is the most stable one, resulting in a lowest thermal boundary resistance. Instead, the Te2-twin boundary structure is the most unstable one, corresponding to a highest thermal boundary resistance. Moreover, the shorter distance between two twin boundaries, the larger the effective thermal boundary resistance is. In a word, twin boundaries cause a 15% reduction in the thermal conductivity of the Bi2Te3 investigated, consistent with the experimental observations.

誌 謝 I
中文摘要 II
Abstract III
表目錄 VIII
圖目錄 IX
第一章 緒論 1
1-1 研究背景 1
1-2 文獻回顧 2
1-2-1 實驗量測 2
1-2-2 分子動力學模擬 3
1-3 研究動機與目的 6
1-4 LAMMPS軟體介紹 7
1-5 論文架構 8
第二章 分子動力學理論 9
2-1 碲化鉍晶體結構介紹 9
2-2 勢能函數 12
2-2-1 碲化鉍勢能函數(一) 13
2-2-2 碲化鉍勢能函數(二) 16
2-3 初始與邊界條件 18
2-3-1 初始位置與速度 18
2-3-2 週期性邊界條件 19
2-4 溫度壓力控制方法 20
2-4-1 溫度控制方法 20
2-4-2 壓力控制方法 23
2-5 非平衡分子動力學 24
2-5-1 熱傳導係數計算 26
2-5-2 去除尺寸效應 27
2-6 收斂測試 28
第三章 單晶碲化鉍分子動力學模擬 30
3-1 平衡分子動力學穩態判斷與資料選取 30
3-2 徑向分佈函數 32
3-3 聲子態密度與色散關係 35
3-4 非平衡分子動力學計算 39
3-4-1 模擬時步大小與總時間設置 40
3-4-2 邊界條件 42
3-4-3 冷熱區與薄層厚度選取 43
3-4-4 穩態判斷與資料選取 44
3-4-5 單晶碲化鉍熱傳導係數 47
3-4-6 薄層熱通量跳動分析 51
第四章 雙晶界碲化鉍分子動力學模擬 55
4-1 雙晶界碲化鉍晶體結構介紹 55
4-2 單一雙晶界結構 56
4-2-1 穩態判斷與資料選取 60
4-2-2 熱傳導係數與界面熱阻 62
4-3 兩併排雙晶界結構 68
4-3-1 穩態判斷與資料選取 70
4-3-2 熱傳導係數與界面熱阻 75
第五章 結論與未來展望 89
5-1 結論 89
5-1-1 單晶碲化鉍 89
5-1-2 雙晶界碲化鉍 90
5-2 未來展望 90
參考文獻 92

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