Ordering and dimensional crossovers in metallic glasses and liquids

Abstract

The atomic-level structures of liquids and glasses are amorphous, lacking long-range order. We characterize the atomic structures by integrating radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu_(46)Zr_(54), Ni_(80)Al_(20), Ni_(33.3)Zr_(66.7), and Pd_(82)Si_(18). Resulting cumulative coordination numbers (CN) show that metallic liquids have a dimension of d=2.55±0.06 from the center atom to the first coordination shell and metallic glasses have d=2.71±0.04, both less than 3. Between the first and second coordination shells, both phases crossover to a dimension of d=3, as for a crystal. Observations from discrete atom center-of-mass position counting are corroborated by continuously counting Cu glass- and liquid-phase atoms on an artificial grid, which accounts for the occupied atomic volume. Results from Cu grid analysis show short-range d=2.65 for Cu liquid and d=2.76 for Cu glass. Cu grid structures crossover to d=3 at ξ ∼ 8Å (∼3 atomic diameters). We study the evolution of local structural dimensions during quenching and discuss its correlation with the glass transition phenomenon.