Abstract
Thermoelectric devices can convert heat and electricity directly, and are used in solid state cooling and waste heat recovery. Owing to the worldwide focus on green energy and sustainable development, thermoelectric devices have attracted intensive research interests. CoSb3 is a skutterudite-structure compound of good thermoelectric properties. It has been reported that the thermoelectric properties of CoSb3 can be further enhanced by alloying with indium. Phase diagrams are materials' basic information, and are useful for understanding of phase formation and transformation, and microstructural evolution of materials. The Co-In-Sb phase diagrams are thus fundamentally important for the development of CoSb3+Indium materials. However, there are limited Co-In-Sb phase diagram literatures available. This study determines the Co-In-Sb phase diagrams experimentally.. The efforts of this study include: (1) determination of the 650 ℃ isothermal section, (2) determination of the 850 ℃ isothermal section, (3) determination of CoSb3-InSb isoplethal section, and (4) determination of liquidus projection. Ternary Co-In-Sb alloys were prepared with pure constituent elements and equilibrated at various temperatures. Their equilibrium phases were determined based on the results of metallographical, compositional and XRD analyses. The (1)-(3) phase diagrams were constructed based on the determined ternary phase equilibria results and available related phase diagrams. The primary solidification phases were determined from the as-quenched alloys and were used for the construction of liquidus projection. The 850 ℃ and 650 oC isothermal sections are similar. No ternary compound is found in this study. Three tie-triangles, Co-CoSb-liquid, CoSb-CoSb2-liquid, and CoSb2-CoSb3-liquid are determined. There are seven phase regions in the CoSb3-InSb isoplethal section, which are liquid, CoSb-liquid, CoSb-CoSb2-liquid, CoSb2-liquid, CoSb2-CoSb3-liquid, CoSb3-liquid, and CoSb3-InSb. There are 9 primary solidification phases in the ternary Co-In-Sb ternary system, including Co, CoIn2, CoIn3, CoSb, CoSb2, CoSb3, InSb, In, and Sb. Seven invariant reactions involving in liquid phase include two class I, four class II, and one class III in the Co-In-Sb ternary system.