Abstract
Since their promising applications in waste heat recovery and solid-state cooling, thermoelectric devices have attracted intensive research efforts. The Bi2Te3-based alloys have good thermoelectric properties. The N-type Bi2Te3-xSex alloys are the most commonly used commercial thermoelectric materials nowadays. It has been reported that their thermoelectric properties can be enhanced with indium doping. Furthermore, indium is also a promising candidate for transient liquid phase bonding of the thermoelectric modules. The efforts of this study include: (1) determination liquidus projection and 250oC isothermal section of Bi-In-Te ternary systems, (2) determination of the 250oC isothermal section of Bi-In-Se ternary systems, (3) In/Bi2Te3 interfacial reactions at 250oC, (4) thermoelectric properties measurement of Bi-In-Te ternary alloys. Ternary alloys are prepared with pure elements. The as-cast alloys are used for the construction of liquidus projection. The primary solidification phases are determined by the results of metallographical, compositional and XRD analyses. No ternary compound is found. There are 14 primary solidification phase regions, including Bi, InBi, In5Bi3, In2Bi, In9Bi, In, In4Te3, InTe, In3Te4, In2Te3, In2Te5, Te, Bi2Te3 and the (Bi2)m(Bi2Te3)n region. There is a miscibility gap in the In4Te3 region. The Bi-In-Te liquidus projection has 12 invariant reactions. Six of their reaction temperatures and reaction types are determined by differential thermal analysis.The 250oC isothermal sections are determined by experiment. There are 10 tie-triangles and 20 two-phase region in the Bi-In-Te ternary system. In addition, ternary compound BiIn2Te4 is found. There are 7 tie-triangles and 15 two-phase region in the Bi-In-Se ternary system.Three IMCs are formed in In/Bi2Te3 couples reacted at 250oC, including In4Te3, InTe, (Bi2)m(Bi2Te3)n. The alternating InTe/Liquid and In4Te3/Liquid layers are observed in reaction couples. Furthermore, some Bi-In-Te ternary alloys are prepared and their thermoelectric properties are measured. The thermal conductivity of alloys is reduced by the secondary phases precipitation, and increase of the ZT value is observed.