The Co-Sb-Ga System: Isoplethal Section and Thermodynamic Modeling

Abstract

The Co-Sb-Ga ternary system is an important thermoelectric material system, and its phase equilibria are in need of further understanding. The CoSb_3-GaSb isoplethal section is experimentally determined in this study. Phase equilibria of the ternary Co-Sb-Ga system are assessed, and the system's thermodynamic models are developed. In addition to the terminal phases and liquid phase, there are six binary intermediate phases and a ternary Co_3Sb_2Ga_4 phase. The Ga solution in the CoSb_3 compound is described by a dual-site occupation (Ga_(VF))_x Co_4Sb_(12−x/2)(GaSb) _(x/2) model. Phase diagrams are calculated using the developed thermodynamic models, and a reaction scheme is proposed based on the calculation results. The calculated results are in good agreement with the experimentally determined phase diagrams, including the CoSb_3-GaSb isoplethal section, the liquidus projection, and an isothermal section at 923 K (650 °C). The dual-site occupation (Ga_(VF))_x Co_4Sb_(12−x/2)(GaSb)_(x/2) model gives good descriptions of both phase equilibria and thermoelectric properties of the CoSb_3 phase with Ga doping.

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