Liquidus projection and isothermal section at 650 °C of ternary Co–Sb–Ga system

Abstract

Co–Sb–Ga ternary system is of interests for thermoelectric applications. Alloys quenched from completely molten state with compositions of the entire Co–Sb–Ga regime and alloys equilibrated at 650 °C with compositions in the CoSb_3–CoGa–Ga–Sb regime were prepared and analyzed. The liquidus projection and isothermal section at 650 °C of ternary Co–Sb–Ga system were determined based on these experimental results and the phase diagrams of its three constituent binary systems. The liquidus projection has 10 primary solidification phase regions. They are Co, CoSb, CoSb_2, CoSb_3, Sb, GaSb, Ga, CoGa_3, CoGa and a ternary compound, Co_3Sb_2Ga_4, which is newly found. There are three class I and six class II invariant reactions involving with liquid phase. Except for the L ↔ Co + CoSb + CoGa, L + CoGa ↔ Co_3Sb_2Ga_4 + GaSb reaction, the reaction temperatures are determined using DTA. In the CoSb_3–CoGa–Ga–Sb region, there are 5 tie-triangles, which are CoSb_3 + Liquid + GaSb, Co_3Sb_2Ga_4 + CoSb_3 + GaSb, CoGa + Co_3Sb_2Ga_4 + GaSb, CoGa + GaSb + CoGa_3, and CoGa_3 + GaSb + Liquid. The ternary solubilities in most of the binary compounds are not significant, and the highest is 3.5 at.% Sb in the CoGa.

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