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A generalized polytetrahedral cluster approach to partial coordination numbers in binary metallic glasses

Partial coordination numbers (CNs) play a substantial role in description of hetero-coordinated local structure and related short-range order in metallic glasses. By defining a polytetrahedral aggregation for solute-solvent type atomic clusters, which retains cluster sphericity, high solute-solvent and solvent-solvent CNs, a preliminary model is developed to estimate the CN of a solute atom within a non-isolated cluster embedded in the glassy environment. Employing the result, a generalized quasi-hard sphere model is constructed by defining intra-and inter-cluster correlations, which can yield significantly close values to experimentally derived partial CNs in a great many metallic glass systems, such as Fe-B, Ni-B, Ni-P, Co-P, Pd-Si, Al-Y, Co-Zr, Co-Ti, Ni-Ti, Zr-Ni, Zr-Pd, Zr-Pt and Cu-Zr. The approach allows evaluation of a complete set of partial CNs in a given binary system as a function of atomic radii and composition.