Ni/CoSb3之界面反應與 Co -Sb -Ga 熱電系統之CoSb3-GaSb 等值剖面圖探討

隨著地球上的人口急速增加，能源的來源及發展成為重要的議題，目前的能源使用中，存在著非常高比例的廢熱。熱電元件能夠將廢熱轉換為電能，吸引了各方的關注與研究開發興趣。開發熱電元件的二項主要議題，分別為探索更優良熱電性質的熱電材料、以提高元件之效率，以及改進熱電元件的可靠性、以提高元件之使用壽命。本研究探討Co-Sb-Ga的相圖與Ni/CoSb3的界面反應，就是針對熱電元件的二項主要議題。CoSb3是一種極具潛力的熱電材料，屬於特殊的晶體結構—skutterudites，已有文獻報導摻雜Ga可有效降低材料的晶格熱傳導係數，使熱電優質大幅提升。本研究探討Co-Sb-Ga三元熱電材料系統中的CoSb3-GaSb等值剖面圖，以提供基礎的相圖資訊。本研究建構了CoSb3-GaSb等值剖面圖，總共分為9個相區，分別為Liquid, CoSb+Liquid, CoSb+CoSb2+Liquid, CoSb2+Liquid, CoSb2+CoSb3 +Liquid, CoSb3+Liquid, CoSb3+GaSb+Liquid, GaSb+Liquid 與 CoSb3 +GaSb.。熱電元件間的界面接合是十分重要的研究議題。由於銲料可能會擴散到熱電材料當中損害熱電性質，因此需在銲料與熱電材料之間加入阻障層防止擴散，並且Ni是常見的阻障層，本研究探討Ni/Sb與Ni/ CoSb3在450oC界面反應。Ni/Sb在450oC下，於界面上出現了三層介金屬相，分別是Ni5Sb2、NiSb以及NiSb2。相的生成順序為Ni/Ni5Sb2/NiSb/NiSb2/Sb，於反應時間24小時下反應層總厚度達到27 μm。在Ni/CoSb3界面上觀察到兩層介金屬相，分別是(Ni,Co)Sb以及Ni5Sb2，並且反應時間20小時下總反應層厚度為22 μm，界面反應結果顯示擴散路徑為Ni/Ni5Sb2/(Ni,Co)Sb/CoSb3，在上述二種反應偶中皆未發現Ni3Sb相。本研究也發現這些界面反應，合理的擴散速率大小，由大至小依序排列為Ni、Co、Sb。

關鍵字

Co-Sb-Ga ；熱電材料；相平衡；等值剖面圖； CoSb3 ； Ni ；界面反應

並列摘要

Energy is among the most critical sustainability issues for human beings due to the rapid growth of world population. However, the energy usage is not efficient and there is a very high percentage of waste heat. Thermoelectric device can convert waste heat directly into electricity, and has attracted a lot of attention and research interests. There are two main subjects in the thermoelectric device development. One is finding materials with better thermoelectric properties, and the other is improving the reliability and enhancing the durability of thermoelectric devices. Focusing on these two subjects, this study determines the Co-Sb-Ga phase equilibria and Ni/CoSb3 interfacial reactions. CoSb3 is a promising thermoelectric material and has a unique skutterudite structure. It has been reported that doping Ga into CoSb3 can reduce its lattice thermal conductivity and significantly enhance its ZT value. One kind of phase diagram of the Co-Sb-Ga ternary system, the CoSb3-GaSb isoplethal section, is determined in this study. This isoplethal section has 9 phase regions which are CoSb+Liquid, CoSb+CoSb2+Liquid, CoSb2+Liquid, CoSb2 +CoSb3+Liquid, CoSb3+Liquid, CoSb3+GaSb +Liquid, GaSb+Liquid, CoSb3+GaSb and Liquid. The joints in thermoelectric devices are also very important. Diffusion barrier is usually introduced between solder and thermoelectric material to prevent their inter-diffusion. Nickel is a common diffusion barrier layer. The interfacial reactions in the Ni/Sb and Ni/CoSb3 couples at 450oC are examined. Three intermetallic phases are formed in the Ni/Sb couple, and the phases in the couple are Ni/Ni5Sb2/NiSb/NiSb2/Sb. The reaction layer becomes thicker with longer reaction time, and it is 27μm after reaction for 24 hours. The NiSb2 phase is not observed in the Ni/CoSb3 couple reacted at 450oC up to 20 hours, and the phases observed are Ni/Ni5Sb2/(Ni,Co)Sb/CoSb3. The thickness of reaction layer is 22 μm after 20 hour-reaction at 450oC. It is concluded that Nickel is the fastest diffusion species.

並列關鍵字

Interfacial reaction ； Thermoelectric ； Phase equilibria ； Isoplethal section

參考文獻

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Ni/CoSb3之界面反應與 Co -Sb -Ga 熱電系統之CoSb3-GaSb 等值剖面圖探討

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