Thermodynamic assessment of the Co-Fe-Sb system

The Co-Fe-Sb ternary system is critically assessed by CALPHAD (CALculation of PHAse Diagram) technique in the present work. The NiAs-type structure phase β-(Co,Fe)Sb with a wide non-stoichiometric range is described by three sublattices, (Sb)1/3(Co,Fe,Va)1/3 (Co,Fe,Va)1/3, following the extension of the sublattices of the phases β(CoSb) and β(FeSb) in the related binaries. The intermetallic compounds ζ(Co,Fe)Sb2 and η(Co,Fe)Sb3 are treated as linear stoichiometric compounds. The liquid, γ(A1)-Fcc_A1, α(A2)-Bcc_A2 and ε(A3)-Hcp_A3 phases are assumed to be substitutional solutions. The Rhombo_A7 phase is considered as the pure Sb phase. The order/disorder transformation between α(A2)-Bcc_A2 and α′(B2)-Bcc_B2 phases is described by a two-sublattice model (Co,Fe,Sb)0.5(Co,Fe,Sb)0.5. A set of self-consistent thermodynamic parameters of the Co-Fe-Sb system is obtained to fit satisfactorily a large amount of experimental data from literature. In the mean while, the Fe-Sb binary system is re-optimized critically.