Structural stability and homogeneity of the nonequilibrium Co-Ag alloys

A realistic n-body potential is derived for the equilibrium immiscible Co-Ag system through fitting its cross potential to some physical properties obtained from ab initio calculations for a few possible nonequilibrium Co-Ag alloys. Based on the derived Co-Ag potential, molecular dynamics simulations reveal that a Co-/Ag-based solid solution can retain its atomic homogeneity up to a critical atomic ratio of 9/12 at.% of Ag/Co, over which the solute atoms begin to segregate and that when the solute atoms exceed 12/18 at.% of Ag/Co, the solid solution becomes unstable and transforms into an amorphous alloy featuring also an inhomogeneous atomic structure, thus predicting a glass-forming range to be within 12-82 at.% of Ag. Moreover, a formation energy diagram is constructed to compare the energetic states of the possible nonequilibrium Co-Ag alloys. For the homogeneous Co-/Ag-based solid solution, a cage-like configuration is proposed to have one solvent atom isotropically surrounded by three nearest shells of solute atoms, and interestingly, the atomic ratio of the proposed configuration is very close to the critical composition of segregation determined by simulations.