以非平衡分子動力學模擬探討碲化鉍雙晶界結構對熱傳性質之影響

An Investigation of the Thermal boundary resistance associated with the Twin Boundary in Bismuth Telluride in use of the non-Equilibrium Molecular Dynamics Simulation

謝宜達(I-Ta Hsieh)

指導教授 ： 黃美嬌

國立臺灣大學/工學院/機械工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201703603

摘要

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。

關鍵字

非平衡分子動力學 ； 碲化鉍 ； 雙晶界 ； 熱傳導係數 ； 界面熱阻

並列摘要

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.

並列關鍵字

NEMD ； Bismuth Telluride ； Twin boundary ； Thermal conductivity ； Thermal boundary resistance

參考文獻

[1] Z.-G. Chen, G. Han, L. Yang, L. Cheng, and J. Zou, "Nanostructured thermoelectric materials: Current research and future challenge," Progress in Natural Science: Materials International, vol. 22, no. 6, pp. 535-549, 2012.

[2] G. S. Nolas, G. A. Slack, J. L. Cohn, and S. B. Schujman, "The next generation of thermoelectric materials," in Seventeenth International Conference on Thermoelectrics. Proceedings ICT98, 1998, pp. 294-297.

[3] M. S. Dresselhaus et al., "New Directions for Low-Dimensional Thermoelectric Materials," Advanced Materials, vol. 19, no. 8, pp. 1043-1053, 2007.

[4] L. D. Hicks and M. S. Dresselhaus, "Thermoelectric figure of merit of a one-dimensional conductor," Physical Review B, vol. 47, no. 24, pp. 16631-16634, 1993.

[5] L. D. Hicks and M. S. Dresselhaus, "Effect of quantum-well structures on the thermoelectric figure of merit," Physical Review B, vol. 47, no. 19, pp. 12727-12731, 1993.