Bi-In-Te、Bi-In-Se三元熱電材料之相平衡與In/Bi2Te3之界面反應

Phase equilibria of the Bi-In-Te, Bi-In-Se ternary thermoelectric materials and In/Bi2Te3 interfacial reactions

陸詩婷(Lu, Shi Ting)

指導教授 ： 陳信文

國立清華大學/工學院/化學工程學系/碩士(2016年)

摘要

Bi2Te3基熱電材料目前已廣泛應用於廢熱回收與熱電致冷領域。根據文獻指出N-型半導體材料Bi2Te3-xSex摻雜In元素，可進一步提升材料熱電性質。商業化熱電元件中存在許多接點，而以In銲料發展過度液相連接技術，對於製程溫度不能太高，卻在較高溫度下運作之熱電模組的應用十分具有潛力。相圖可提供材料微結構與生成相的基本知識。本研究針對Bi-In-Te、Bi-In-Se三元系統進行探討，分析結果包含:(1)以實驗建構Bi-In-Te三元系統之液相線投影圖以及於250oC等溫橫截面圖(2)以實驗建構Bi-In-Se三元系統於250oC等溫橫截面圖(3)探討In/Bi2Te3於250oC界面反應的生成相、反應機制與路徑(4)Bi-In-Te三元合金之熱電性質量測。本研究以純元素配製不同組成之三元合金；液相線部分對於as-cast的合金進行分析，判斷相區邊界與不變反應點之溫度、類別；將合金置於250oC高溫爐進行相平衡以建構等溫橫截面圖；於250oC接合定量銲料與基材，進行液/固界面反應實驗。以SEM、EPMA與XRD進行微結構分析、組成分析與相鑑定，並針對部分三元合金進行熱電量測。在Bi-In-Te三元系統液相線投影圖之分析結果，並沒有發現三元相的出現。此系統含有14個首要析出相區，分別為Bi、InBi、In5Bi3、In2Bi、In9Bi、In、In4Te3、InTe、In3Te4、In2Te3、In2Te5、Te、Bi2Te3以及(Bi2)m(Bi2Te3)n相區，在In4Te3相區內有一不互溶區。此系統包含12個不變反應點，利用熱分析決定其中6個反應點的溫度與種類，包含1個Class I、4個Class II以及1個Class III。在250oC等溫橫截面圖的分析結果，Bi-In-Te三元系統含有10個三相區與20個兩相區，以及1個三元相BiIn2Te4存在；Bi-In-Se三元系統含有7個三相區與15個兩相區。在In/Bi2Te3於250oC之液/固界面反應中，觀察到In4Te3、InTe、(Bi2)m(Bi2Te3)n生成相與Liquid相固化形成之交錯微結構。最後針對部分Bi-In-Te三元合金進行熱電性質量測，探討析出相造成熱導率降與
熱電優值提升之相對關係。

關鍵字

熱電材料 ； 碲化鉍 ； 銦 ； 相圖 ； 液相線投影圖 ； 等溫橫截面圖 ； 界面反應

並列摘要

Since their promising applications in waste heat recovery and solid-state cooling, thermoelectric devices have attracted intensive research efforts. The Bi2Te3-based alloys have good thermoelectric properties. The N-type Bi2Te3-xSex alloys are the most commonly used commercial thermoelectric materials nowadays. It has been reported that their thermoelectric properties can be enhanced with indium doping. Furthermore, indium is also a promising candidate for transient liquid phase bonding of the thermoelectric modules. The efforts of this study include: (1) determination liquidus projection and 250oC isothermal section of Bi-In-Te ternary systems, (2) determination of the 250oC isothermal section of Bi-In-Se ternary systems, (3) In/Bi2Te3 interfacial reactions at 250oC, (4) thermoelectric properties measurement of Bi-In-Te ternary alloys. Ternary alloys are prepared with pure elements. The as-cast alloys are used for the construction of liquidus projection. The primary solidification phases are determined by the results of metallographical, compositional and XRD analyses. No ternary compound is found. There are 14 primary solidification phase regions, including Bi, InBi, In5Bi3, In2Bi, In9Bi, In, In4Te3, InTe, In3Te4, In2Te3, In2Te5, Te, Bi2Te3 and the (Bi2)m(Bi2Te3)n region. There is a miscibility gap in the In4Te3 region. The Bi-In-Te liquidus projection has 12 invariant reactions. Six of their reaction temperatures and reaction types are determined by differential thermal analysis.The 250oC isothermal sections are determined by experiment. There are 10 tie-triangles and 20 two-phase region in the Bi-In-Te ternary system. In addition, ternary compound BiIn2Te4 is found. There are 7 tie-triangles and 15 two-phase region in the Bi-In-Se ternary system.Three IMCs are formed in In/Bi2Te3 couples reacted at 250oC, including In4Te3, InTe, (Bi2)m(Bi2Te3)n. The alternating InTe/Liquid and In4Te3/Liquid layers are observed in reaction couples. Furthermore, some Bi-In-Te ternary alloys are prepared and their thermoelectric properties are measured. The thermal conductivity of alloys is reduced by the
secondary phases precipitation, and increase of the ZT value is observed.

並列關鍵字

Thermoelectric materials ； Bi2Te3 ； In ； Phase diagram ； Liquidus projection ； Isothermal section ； Interfacial reaction

參考文獻

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