熱電元件能夠將廢熱轉換為電能，提高能源使用之效率。當熱電元件與太陽能加熱元件搭配，是具潛力的再生能源。熱電元件通常具多組P型與N型熱電材料，結構內部有許多不同材料的接合點，需要引入適合的阻障層。Sb2Te3 與Ge2Sb2Te5為重要的熱電材料，Co與Ni是常見的阻障層材料。本研究探討CoxNi1-x/Sb2Te3與CoxNi1-x/Ge2Sb2Te5界面反應，以作為評估CoxNi1-x是否為合適阻障層之基礎。本研究也進行Co-Sb-Te、Ni-Sb-Te 與 Co-Ni-Sb-Te相關系統的相平衡探討，提供基礎的相平衡知識，也有助於了解界面反應。
界面反應是以反應偶的實驗進行探討。以純Ge、純Sb與純Te製備基材，於基材上以電鍍方法鍍上Co、Ni與(Co,Ni)合金，製備成反應偶。再將反應偶放入高溫爐進行反應，經過一段時間後取出，觀察分析界面反應，並探討其擴散機制。本研究的界面反應探討，包括了Co/Sb2Te3與Ni/Sb2Te3於200℃、300℃、400℃及500℃， Ni0.8Co0.2/Sb2Te3於400℃及500℃，以及 Co/Ge2Sb2Te5與Ni/Ge2Sb2Te5於500℃。本研究分析的界面反應，包括了界面相成長的型態、組成、種類與厚度。佐以相平衡知識，分析界面反應擴散路徑與首要的擴散元素。
相平衡探討的部分，是以純元素製備Co-Sb-Te與Ni-Sb-Te三元合金，封入於石英管中後，置入高溫爐中進行相平衡實驗。經過一段時間之後取出淬冷於水中，以金相分析、組成分析與粉末X-光繞射分析，來分析試樣合金中的平衡生成相。以三元相平衡實驗的結果，搭配相關二元與三元系統的相平衡文獻，依據熱力學知識來測定推知Co-Sb-Te與Ni-Sb-Te在400℃與500℃的等溫橫截面相圖。依據相關的二元系統與三元系統相圖資料，本研究也推測了Co-Ni-Sb-Te四元系統在400℃與500℃的等溫四面體相圖。
在Co-Sb-Te系統中，在400℃與500℃的平衡相，沒有發現三元相存在。Co-Sb-Te的400℃的等溫橫截面有10個單相區與7個三相區。單相區分別為Co、Sb、Te、CoSb、Co(Sb,Te)2、CoSb3、δ-(Sb2Te)、γ-(SbTe)、Sb2Te3、Co2Te3。500℃的等溫橫截面有10個單相區與7個三相區。與400℃比較，由於500℃高於Te熔點，因此單相區多了liquid相而少了Te相，而三相區多了Co(Sb,Te)2-Sb2Te3-liquid，少了Co(Sb,Te)2-Sb2Te3-Te。
Co/Sb2Te3在200℃反應發現界面並無生成相。於300℃下反應50天厚度約為4.5µm和400℃下反應40天厚度約為11.1µm，生成相分別為含有Sb之CoTe2與Co(Sb,Te)2，前者擴散路徑為Co/CoTe2/Sb2Te3，後者為Co/Co(Sb,Te)2/Sb2Te3，Co皆為主要擴散元素，厚度隨時間與溫度增加而增加；而500℃下Co/Sb2Te3反應30天厚度約為109.1µm，生成Co(Sb,Te)2與Co2Te3相。
在Ni-Sb-Te系統中，已有文獻完成400℃等溫橫截面，本研究則探討了500℃等溫橫截面。文獻中400℃等溫橫截面存在兩個三元相NiSb1-xTe2x、Ni5.66SbTe2，本研究在500℃等溫橫截面與界面反應中也確認了這兩個相的存在。Ni-Sb-Te的400℃的等溫橫截面有14個單相區與12個三相區。單相區分別為Ni、Sb、Te、Ni3Sb、Ni7Sb3、NiSb2、δ-(Sb2Te)、γ-(SbTe)、Sb2Te3、γ1-Ni1.3Te、β2-Ni3Te2、NiSb1-xTe2x、Ni5.66SbTe2、Ni(Sb1-xTex)1+y。500℃的等溫橫截面有14個單相區與13個三相區。與400℃比較，由於500℃高於Te熔點，因此單相區多了liquid相少了Te相，而三相區少了NiSb2-Sb2Te3-δ-(Sb2Te)、Ni(Sb1-xTex)1+y-Sb2Te3-Te，多了NiSb2-Sb2Te3-γ-(SbTe)、NiSb2-γ-(SbTe)-δ-(Sb2Te)、Ni(Sb1-xTex)1+y-Sb2Te3-liquid。
Ni/Sb2Te3在200℃(反應15天厚度約為5.2µm)、300℃(反應10天厚度約為6.7µm)與400℃(反應15天厚度約為13.6µm)，生成相皆為NiSb1-xTe2x三元相，擴散路徑為Ni/NiSb1-xTe2x/Sb2Te3。在500℃下短時間(6小時厚度約為18.7µm)生成相為Ni(Sb1-xTex)1+y，長時間(1天厚度約為66.0µm)生成一層單相區Ni(Sb1-xTex)1+y與一層兩相區Ni(Sb1-xTex)1+y+Ni5.66SbTe2，短時間下擴散路徑為Ni/Ni(Sb1-xTex)1+y/Sb2Te3，而長時間下擴散路徑為Ni/Ni(Sb1-xTex)1+y+Ni5.66SbTe2/Ni(Sb1-xTex)1+y/Sb2Te3，Ni皆為主要擴散元素。
Ni0.8Co0.2/Sb2Te3界面情形與Ni/Sb2Te3相同，生成相中幾乎沒有Co，在400℃下(3天厚度約為24.0µm)擴散路徑為Ni0.8Co0.2/Ni2Sb1-xTe2x/Sb2Te3，而在500℃下短時間(6小時厚度約為40.0µm)擴散路徑為Ni0.8Co0.2/Ni(Sb1-xTex)1+y/Sb2Te3，長時間(2天厚度約為90.0µm)擴散路徑為Ni0.8Co0.2/Ni(Sb1-xTex)1+y/Ni(Sb1-xTex)1+y+Ni5.66SbTe2/Sb2Te3，Ni為主要擴散元素，Co幾乎不擴散。
本研究Co/Ge2Sb2Te5、Ni/Ge2Sb2Te5進行500℃之界面反應，觀察其生成之介金屬，發現於500℃下Co/Ge2Sb2Te5生成相含有一個兩相區CoGe+CoTe2以及兩個單相區β-GeTe、Co2Te3；Ni/Ge2Sb2Te5生成相為Ni5Ge3+Ni(Sb1-xTex)1+y，擴散路徑為Ni/Ni5Ge3+Ni(Sb1-xTex)1+y/Ge2Sb2Te5，Ni為主要擴散元素。
值得一提的是，本研究中所使用的熱電材料Sb2Te3、Ge2Sb2Te5，兩者在500℃下皆可在Co鍍層表面發現反應層，推測其為基材氣相與Co發生反應，故無法討論其擴散路徑，而在本文進行相關Sb2Te3氣相實驗以驗證此推測。

Thermoelectric modules can convert waste heat directly into electrical energy to improve the efficiency of energy use. When thermoelectric modules are used with solar heating device, it is a potential renewable energy source. Thermoelectric modules usually consist of multiple pairs of P-type and N-type thermoelectric materials. There are many joints of different materials inside the structure, so it is necessary to introduce adequate diffusion barrier layers. Sb2Te3 and Ge2Sb2Te5 are important thermoelectric material. Co and Ni are common barrier materials. To understand whether CoxNi1-x is an adequate barrier, this study aims to understand the interfacial reactions of CoxNi1-x/Sb2Te3 and CoxNi1-x/Ge2Sb2Te5. Phase diagrams provide phase equilibria knowledge and help us understand the interfacial reaction, so this study also discusses Co-Sb-Te、Ni-Sb-Te and Co-Ni-Sb-Te phase equilibria.
Interfacial reactions are discussed by reaction couple experiment. The substrates are prepared with pure constituent elements and electroplated with Co, Ni, and (Ni,Co) alloy to get the reaction couples. The obtained couples were sealed under vacuum and heated in furnaces and took out after selected reaction time to observe the interface and discuss the diffusion mechanism. This study examines the interfacial reactions in Co/Sb2Te3 and Ni/Sb2Te3 couples at 200℃, 300℃, 400℃, and 500℃ respectively. Ni0.8Co0.2/Sb2Te3 reacts at 400℃ and 500℃. The interfacial reactions analyzed in this study include type, composition, and thickness of the reaction phase growth . With the knowledge of phase equilibria, the interfacial reaction paths and the fastest diffusion element are analyzed.
The alloys for phase equilibria were prepared by pure constituent elements and then sealed in quartz ampoules. The ampoules were heated in furnaces. After selected reaction time, the ampoules were quenched into water and then the samples were analyzed by EPMA and powder X-ray diffraction. Co-Sb-Te and Ni-Sb-Te isothermal sections at 400℃ and 500℃ are confirmed with the experiment results and the literature of binary and ternary related system. This study also predicts the isothermal tetrahedron of the Co-Ni-Sb-Te at 400℃ and 500℃.
In Co-Sb-Te system, There is no observed ternary phase at 400℃、500℃. At 400℃, Co-Sb-Te system contains 10 single-phase regions and 7 three-phase regions. The 10 single-phase regions are Co, Sb, Te, CoSb, Co(Sb,Te)2, CoSb3, δ-(Sb2Te), γ-(SbTe), Sb2Te3, and Co2Te3. At 500℃, Co-Sb-Te system also contains 10 single-phase regions and 7 three-phase regions. Compared to the isothermal section at 400℃, the 500℃ isothermal section contains not Te phase but liquid phase because 500℃ is higher than Te melting point. Therefore, one of the three-phase regions at 500℃ is Co(Sb,Te)2-Sb2Te3-liquid instead of Co(Sb,Te)2-Sb2Te3-Te.
At 200℃ Co/Sb2Te3, there is no reaction layer observed. At 300℃(the reaction layer thickness is about 4.5µm for 50 days) and 400℃(the reaction layer thickness is about 11.1µm for 40 days), the former reaction phase is CoTe2 with high Sb solubility and the latter is Co(Sb,Te)2. The diffusion path at 300℃ is Co/CoTe2/Sb2Te3. The diffusion path at 400℃ is Co/Co(Sb,Te)2/Sb2Te3. Co is the fastest diffusing element. At 500℃(the reaction layer thickness is about 109.1µm for 30 days), the reaction phases are Co(Sb,Te)2 and Co2Te3
In Ni-Sb-Te system, NiSb1-xTe2x and Ni5.66SbTe2 were found at 400℃ according to the literature. This study explores the isothermal section at 500℃, and also confirms the two ternary compounds exist based on the the isothermal section and Ni/Sb2Te3 at 500℃. At 400℃, Ni-Sb-Te system contains 14 single-phase regions and 12 three-phase regions. The 14 single-phase regions are Ni, Sb, Te, Ni3Sb, Ni7Sb3, NiSb2, δ-(Sb2Te), γ-(SbTe), Sb2Te3, γ1-Ni1.3Te, β2-Ni3Te2, NiSb1-xTe2x, Ni5.66SbTe2 and Ni(Sb1-xTex)1+y. At 500℃, Ni-Sb-Te system contain 14 single-phase regions and 13 three-phase regions. Compared to the isothermal section at 400℃, the 500℃ isothermal section contains not Te phase but liquid phase because 500℃ is higher than Te melting point. One of the three-phase regions at 500℃ is Ni(Sb1-xTex)1+y-Sb2Te3-liquid instead of Ni(Sb1-xTex)1+y-Sb2Te3-Te, and the isothermal dosen’t contain NiSb2-Sb2Te3-δ-(Sb2Te) but NiSb2-Sb2Te3-γ-(SbTe) and NiSb2-γ-(SbTe)-δ-(Sb2Te).
Ni/Sb2Te3 at 200℃(the reaction layer thickness is about 5.2µm for 15 days), 300℃(the reaction layer thickness is about 6.7µm for 10 days)and 400℃(the reaction layer thickness is about 13.6µm for 15 days), the three reaction phases are NiSb1-xTe2x. The diffusion path is Ni/NiSb1-xTe2x/Sb2Te3. At 500℃, the reaction phase depends on the reaction time. For shorter time(the reaction layer thickness is about 18.7µm for 6 hours), the reaction phase is Ni(Sb1-xTex)1+y and the diffusion path is Ni/Ni(Sb1-xTex)1+y/Sb2Te3. For longer time(the reaction layer thickness is about 66.0µm for 1 day), the reaction phase is a two-phase region, which contains Ni(Sb1-xTex)1+y and Ni5.66SbTe2, and the diffusion path is Ni/Ni(Sb1-xTex)1+y+Ni5.66SbTe2/Ni(Sb1-xTex)1+y/Sb2Te3. Ni is the fastest diffusing element at 200℃, 300℃, 400℃, and 500℃.
The reaction phase for Ni0.8Co0.2/Sb2Te3 is same as Ni/Sb2Te3 at 400℃ and 500℃. Co nearly doesn’t diffuse. At 400℃(the reaction layer thickness is about 24.0µm for 3 days), the diffusion path is Ni0.8Co0.2/Ni2Sb1-xTe2x/Sb2Te3. At 500℃, the reaction phase depends on the reaction time. For shorter time(the reaction layer thickness is about 40.0µm for 6 hours), the reaction phase is Ni(Sb1-xTex)1+y and the diffusion path is Ni0.8Co0.2/Ni(Sb1-xTex)1+y/Sb2Te3. For longer time(the reaction layer thickness is about 90µm for 2 days), the reaction phase is a two-phase region, which contains Ni(Sb1-xTex)1+y and Ni5.66SbTe2, and the diffusion path is Ni0.8Co0.2/Ni(Sb1-xTex)1+y/Ni(Sb1-xTex)1+y+Ni5.66SbTe2/Sb2Te3. Ni is the fastest diffusing element at 400℃ and 500℃.
This study observed the reaction phase of Co/Ge2Sb2Te5 and Ni/Ge2Sb2Te5 at 500℃. For Co/Ge2Sb2Te5, there is a two-phase region and two single-phase regions. The two-phase region is CoGe and Co(Co,Te)2, and the two single-phase region are β-GeTe and Co2Te3. For Ni/Ge2Sb2Te5, the reaction phase is a two phase region, which contains Ni5Ge3 and Ni(Sb1-xTex)1+y. The diffusion path of Ni/Ge2Sb2Te5 is Ni/Ni5Ge3+Ni(Sb1-xTex)1+y/Ge2Sb2Te5, Ni is the fastest diffusing element.
It’s also worth mentioning that there is reaction layer on the Co surface in Co/Sb2Te3 and Co/Ge2Sb2Te5. It’s is assumed that substrate vapor react with Co on the surface. This study shows the experiment results of Sb2Te3 gas phase reaction to prove this assumption.

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