利用密度泛函理論開發高效率矽鍺錫熱電合金;Designing SiGeSn Alloys for Thermoelectric Applications Using Density Functional Theory

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Title:	利用密度泛函理論開發高效率矽鍺錫熱電合金;Designing SiGeSn Alloys for Thermoelectric Applications Using Density Functional Theory
Authors:	林俐玟;Lin, Li-Wen
Contributors:	化學工程與材料工程學系
Keywords:	密度泛函理論;熱電材料;矽鍺錫合金;品質因數;熱導率;半導體;DFT;thermoelectric material;SiGeSn alloys;figure of merit;thermal conductivity;semiconductor
Date:	2024-08-14
Issue Date:	2024-10-09 15:28:10 (UTC+8)
Publisher:	國立中央大學
Abstract:	隨著綠色能源需求的持續增加，尋找有前景的綠色能源材料至關重要。熱電(TE)材料能夠有效地將廢熱轉換為電能，這不僅可以提高能源利用效率，還能減少對傳統能源資源的依賴。為了評估熱電材料的能量轉換效率，可以通過品質因數(zT)來確認，而提升zT值的方法包括提高Seebeck coefficient、電導率(Electrical conductivity)或降低熱導率(Thermal conductivity)。其中，SiGe合金以其出色的熱電轉換效率著稱，尤其是含有20% Ge的SiGe合金，在高溫熱電應用中表現出色。此外，研究發現，若在SiGe合金中添加Sn，會造成成分無序和晶格變形，導致強烈的非簡諧聲子-聲子散射，從而大幅降低熱導率，使得SiGeSn合金成為一種非常有前景的熱電材料。本研究使用密度泛函理論(DFT) 探討添加Sn元素於SiGe合金對熱電性質的影響，並找尋具有最佳熱電轉換效率的Si4Ge1Snx合金比例。在保持Si/Ge比例為4的狀況下，通過計算改變了Sn元素組成比例，從0到4，建立了一系列Si4Ge1Snx合金。透過以下這些計算研究了Si4Ge1Snx合金的電子特性，包括Seebeck coefficient、電導率、熱導率和功率因數(Power factor)來評估它們的熱電性能。研究發現，當Sn含量(x)在0到4之間時會表現出n型熱電半導體的特性，且隨著溫度的升高，該合金的zT值也會增加，特別是在1300K的高溫下，Si4Ge1Sn1合金的zT值達到了 2.05，且同時具有優異的機械穩定性和動態穩定性，顯示出Si4Ge1Sn1合金作為熱電材料的應用前景。此外，隨著Sn含量的添加，晶格熱導率降低，但同時保持電導率不變，進一步影響了zT值。另外，隨著溫度升高，電子熱導率的影響變得更加顯著。最後，從研究中可以發現，添加Sn確實可以提升材料的熱電性能，並在Sn含量為1且溫度為1300K時達到最佳效果。然而，當Sn含量超過1時，zT 值會逐漸下降。總結來說，本研究證實了Si4Ge1Sn1合金在熱電材料方面的巨大潛力，特別是作為高溫熱電材料，展示出優異的性能和應用前景。;With the increasing demand for clean energy sources, finding promising energy alternatives is crucial for society. Thermoelectric (TE) materials offer a green energy solution by enabling the reversible conversion between thermal and electrical energy. The figure of merit (zT) can be used to evaluate the energy conversion efficiency of thermoelectric materials, and methods to enhance zT include increasing the Seebeck coefficient, electrical conductivity, or decreasing thermal conductivity. SiGe alloys, known for their effective waste heat recovery, especially those containing 20% Ge content, exhibit excellent properties for high-temperature TE applications. Moreover, the addition of Sn to SiGe alloys can further reduce thermal conductivity because it causes compositional disorder and lattice distortion, leading to strong anharmonic phonon-phonon scattering. These characteristics make SiGeSn alloys promising candidates for thermoelectric materials. In this study, density functional theory (DFT) was applied to search for the optimal composition of Si4Ge1Snx alloys for thermoelectric applications. A series of SiGeSn alloys were constructed by varying the composition, with the Sn ratio ranging from 0 to 4 while maintaining the Si/Ge ratio at 4. Electronic characteristics of SiGeSn alloys were calculated, and their thermoelectric properties, including the Seebeck coefficient, electronic conductivity, thermal conductivity, and power factor, were assessed. The conversion efficiency of TE materials was determined using the figure of merit (zT). Compositions with Sn content (x) ranging from 0 to 4 exhibited n-type thermoelectric behavior. Particularly, The Si4Ge1Sn1 alloy is found to have the optimal composition with the highest zT value of 2.05 with excellent mechanical stability, revealing the promising applications of SiGeSn alloys as thermoelectric materials. It is also found that the zT value is mainly determined by their thermal conductivity. In addition, while increasing the Sn content, the lattice thermal conductivity decreases while the electrical conductivity remains unchanged, thereby affecting the zT value. Furthermore, as temperature rises, the contribution of electronic thermal conductivity becomes more significant. Research indicates that with the addition of Sn, the power factor increases and reach to its maximum at x = 1 at temperature of 1300K. However, when the Sn > 1, the zT value gradually declines.This work confirms the significant potential of Si4Ge1Sn1 alloy as thermoelectric materials, particularly for high-temperature applications, showcasing excellent performance and promising prospects.
Appears in Collections:	[National Central University Department of Chemical & Materials Engineering] Electronic Thesis & Dissertation

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