Nanoscale phase separation and local icosahedral order in amorphous alloys of immiscible elements

We demonstrate that local icosahedral ordering, as well as spinodal compositional modulations with nanometer scale wavelengths, are characteristic of amorphous structures formed in an immiscible system with large positive heat of mixing. This unique nature of the atomic-level structures allows the amorphous alloy to lower its enthalpy such that the heat of crystallization is of a magnitude comparable to that typically seen for amorphous phases in easy glass-forming systems. The development of such chemical decomposition and topological order in the short to medium range has been monitored in the Ag-Ni model system using molecular dynamics (MD) simulations. The MD findings of the structural features and enthalpies, as well as their correlation, are consistent with the experimental characterization results of vapor-deposited Ag-Ni amorphous phases.