Structural stability and characteristics of the metastable Ag-W phases studied by ab initio and molecular dynamics calculations

For the immiscible Ag-W system, ab initio calculations identify the relatively stable structures of the metastable Ag75W25, AgW, and Ag25W75 phases to be L6(0), B2, and L1(2), respectively. Based on a newly derived Ag-W potential under an extended Finnis-Sinclair formalism, molecular static and dynamics calculations predict that for the Ag100-xWx alloy, a bcc structure is more stable than a fcc one when 80 < x <= 100, and that bcc and fcc structures have almost similar formation energies when 0 <= x < 80. Moreover, molecular dynamics simulations show that an amorphous state has lower formation energy than its fcc or bcc counterpart in a composition range of 20 <= x <= 80, which is therefore the glass-forming ability/range of the Ag-W system. Interestingly, moderate phase segregation is observed in the Ag-W amorphous alloy upon simulations, and the segregation tendency is found to strongly depend on the alloy composition as well as on the temperature. (c) 2007 American Institute of Physics.