熱電元件能夠直接將熱與電進行轉換，是目前能源研究矚目的焦點。PbTe在300-600oC溫度區間具有良好的熱電性質，為具潛力之中溫熱電材料。熱電元件中有許多接點，根據熱電元件之應用溫度不同，必須尋找對應其溫度區間的銲料；其中Ag-41.0at.%Sb共金合金之熔點為485oC，適用於中溫熱電材料。而Ni與Co為常見之擴散阻障層，可防止銲料與熱電材料劇烈反應。為了作為提升熱電元件使用之效率及可靠度，接點間之界面反應為一項重要的研究。相圖為材料系統之基礎，有助於對界面反應之研究。因此本研究探討：(1)實驗方法建構之Ag-Ni-Sb三元系統400oC與550oC等溫橫截面圖。(2) Ag-Ni-Sb三元系統計算相圖。(3)350oC與550oC之Ni/Ag-Sb界面反應。(4)350oC與550oC之Co/Ag-Sb界面反應。(5)350oC與550oC之Co/PbTe界面反應。實驗結果以SEM進行金相分析，以EPMA進行組成分析，以XRD進行結構分析。
依據實驗與計算結果已訂定出400oC 與550oC之 Ag-Ni-Sb等溫橫截面圖，其中並未發現三元相的存在，且所有二元相對第三元的溶解度皆非常低。400oC時共有7個三相區，其中Ag3Sb+NiSb2+Sb、Ag+Ni5Sb2+NiSb、Ag+(Ni3Sb)+Ni5Sb2和Ag+Ni+(Ni3Sb)由實驗決定。550oC時共確立9個三相區，其中Sb+liquid+NiSb2、liquid+NiSb+NiSb2、liquid+Ag3Sb+NiSb和Ag+Ni+(Ni3Sb)由實驗確認。Ni/Ag-Sb於350oC之界面反應中可觀察到NiSb相與NiSb2相的生成；於550oC時則觀察到Ni3Sb相、Ni5Sb2相與NiSb相。根據生成相的型態，推論擴散速率最快的元素為Sb。Co/Ag-Sb於350oC之反應偶僅生成CoSb相；而於550oC時則可發現CoSb相與CoSb3相的存在。以生成相之生成順序推論擴散速率最快的元素為Sb。本研究觀察到Co/Ag-Sb反應偶之生成相較脆，Ni/Ag-Sb反應偶具良好接合性質，且Ni/Ag-Sb界面反應與Ni/商用銲料反應之介金屬相成長速率相當，因此推論Ag-Sb共晶合金適合以Ni作為阻障層，用於中溫熱電材料。Co/PbTe於350oC與550oC皆未有介金屬相生成，且兩者接合性良好，因此推論Co適合作為PbTe之擴散阻障層。

Thermoelectric devices convert waste heat directly into electricity, enhance energy usage efficiencies, and have attracted a lot of research interests. The PbTe compound has good thermoelectric properties and is promising for thermoelectric devices in the temperature range of 300-600oC. Usually, there are many joints in a thermoelectric module. Because of their different application temperatures, different solders/brazes with different melting points are needed. Ag-Sb eutectic alloy, of which melting point is 485oC, is a promising candidate as the joining materials for the mid-temperature thermoelectric modules. Ni and Co are commonly used as barrier layers to prevent interfacial reactions between joining materials and thermoelectric materials. Therefore, the study in the interfacial reactions among thermoelectric material, barrier layer and joining material is crucial for the efficiencies and reliabilities of a thermoelectric device. Phase diagrams contain phase equilibria information and are fundamentally important for understanding and illustration of interfacial reactions. This study thus includes the following discussions: (1) experimental determination of the Ag-Ni-Sb isothermal sections at 400oC and 550oC, (2) thermodynamic calculation of the Ag-Ni-Sb isothermal section, (3) Ni/Ag-Sb interfacial reactions at 350oC and 550oC, (4) Co/Ag-Sb interfacial reactions at 350oC and 550oC, and (5) Co/PbTe interfacial reactions at 350oC and 550oC. In this study, the metallographic analysis, compositions, and structures are determined by SEM, EPMA, and XRD.
Similar results are found in the Ag-Ni-Sb isothermal sections at 400oC and 550oC. No ternary compounds are observed and all the binary compounds have very limited ternary solubilities. There are 7 tie-triangles at 400oC. The Ag3Sb+NiSb2+Sb, Ag+Ni5Sb2+NiSb, Ag+(Ni3Sb)+Ni5Sb2, and Ag+Ni+(Ni3Sb) tie-triangles have been experimentally determined. In addition, there are 9 tie-triangles at 550oC. The Sb+liquid+NiSb2, liquid+NiSb+NiSb2, liquid+Ag3Sb+NiSb, and Ag+Ni+(Ni3Sb) tie-triangles have been experimentally determined. Two intermetallic phases are observed in the Ni/Ag-Sb couples reacted at 350oC, and they are NiSb and NiSb2. Ni3Sb, Ni5Sb2 and NiSb are formed in the Ni/Ag-Sb couples reacted at 550oC. According to the phase formation sequence and morphologies, it is concluded that Sb is the fastest diffusion species. One intermetallic phase, CoSb, is observed in the Co/Ag-Sb couples reacted at 350oC. Two intermetallic phases are found in the Co/Ag-Sb couples reacted at 550oC, and they are CoSb and CoSb3. According to the reaction microstructures, Sb is the fastest diffusion species. The IMCs in the Co/Ag-Sb couples are brittle. The Ag-Sb has good wetting toward the Ni substrate. The reaction rates of Ag-Sb eutectic alloys with Ni are comparable to those of commercial solders with Ni. Thus, Ni is a proper barrier layer for Ag-Sb eutectic alloy, and Ag-Sb eutectic alloy is a suitable braze for the mid-temperature thermoelectric modules. No intermetallic phase is in the Co/PbTe couples at 350oC and 550oC. The wettability between Co and PbTe is good. Co thus can be a suitable barrier layer for PbTe.

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