| Summary: | 碩士 === 國立清華大學 === 化學工程學系所 === 106 === Thermoelectrics have attracted a lot of research interests primarily because of their potentials in enhancing the energy usage efficiency and as renewable energy sources when used together with solar heating panels. Bi2(Sb,Te)3 and Bi2(Se,Te)3 are the most commonly used thermoelectric materials. It has been reported that their thermoelectric properties could be improved with indium doping. There are usually numerous joints in thermoelectric modules. Indium-containing alloys are frequently used as solders. Phase diagrams provide fundamental information and are essential for materials understanding and development. Knowledge of interfacial reactions is critical for the reliability assessment of joints. This study has two parts. One part is the determination of phase diagram, Bi-In-Se liquidus projection, and the other part is interfacial reaction investigation of the In/Bi2Se3 interfacial reactions. The related data are previously lacking in the literature but are important for the development of the Bi2(Sb,Te)3 and Bi2(Se,Te)3-based thermoelectric modules. The experimental determinations of the Bi-In-Se liquidus projection reveal, except for Se regime, the primary solidification phases are Bi2Se3, In2Se3, In6Se7, InSe, In4Se3, In, , BiIn2, Bi3In5, BiIn, Bi, and (Bi2)m(Bi2Se3)n phases, respectively. The invariant reactions include L=In2Se3+Bi2Se3+Se, L+In2Se3+InSe=In6Se7, L+Bi+InSe=In2Se3, L+In2Se3=(Bi2)m(Bi2Se3)n+Bi, L+In2Se3=Bi2Se3+(Bi2)m(Bi2Se3)n, L+InSe=Bi+BiIn, L+InSe=In4Se3+BiIn2, L+In4Se3+In=, L+InSe+BiIn=Bi3In5, L+InSe=Bi3In5+BiIn2, and L=In4Se3+BiIn2+. There are three saddle points and three miscibility gaps in the system. The second part is the interfacial reactions between Indium and Bi2(Se,Te)3 thermoelectric materials. Those reacted couples are In/Bi2Te3 at 140, 200, 400oC, In/Bi2Se3 at 100, 140, 200, 250, 400oC, In/(Sb,Bi)2Te3 at 140, 200, 250oC, and In/Bi2(Se,Te)3 at 200, 250oC. Ternary intermetallic compound is found in the solid/solid couples In/(Sb,Bi)2Te3 reacted at 140oC meanwhile no significant interfacial reactions are found in In/Bi2Se3 couples reacted at 140oC for up to 90 days. Complex and significant interfacial reactions occur in all the liquid/solid. For example, In4Se3, InSe, In2Se3 and (Bi2)m(Bi2Se3)n phases in the In/Bi2Se3 couples reacted at 250oC and In4Te3, InTe and In3Te3-x(Sb,Bi)x phases in the In/(Sb,Bi)2Te3 at 250oC are observed. All the phase micrographs and the compositions are determined using Scanning Electron Microscope (SEM) and electron probe microanalysis (EPMA). The crystal diffractions and invariant temperatures were examined using X-ray powder diffraction (XRD) and differential thermal analysis (DTA), respectively.
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