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

Abstract

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.