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

The Co-Sb-Ga ternary system is an important thermoelectric material system, and its phase equilibria are in need of further understanding. The CoSb3-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 Co3Sb2Ga4 phase. The Ga solution in the CoSb3 compound is described by a dual-site occupation (Ga-VF) (x) Co4Sb12-x/2(Ga-Sb) (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 CoSb3-GaSb isoplethal section, the liquidus projection, and an isothermal section at 923 K (650 A degrees C). The dual-site occupation (Ga-VF) (x) Co4Sb12-x/2(Ga-Sb) (x/2) model gives good descriptions of both phase equilibria and thermoelectric properties of the CoSb3 phase with Ga doping. (C) The Minerals, Metals & Materials Society and ASM International 2015