Ni/CoSb3 interfacial reactions and CoSb3-GaSb isoplethal section in the Co-Sb-Ga ternary thermoelectric material system

• Main Authors: Chen, Wei-an, 陳韋安
• Other Authors: Chen, Sinn-wen
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/04260235710889409887

碩士 === 國立清華大學 === 化學工程學系 === 102 === 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.