Percolation structure in metallic glasses and liquids

The atomic-level structures of liquids and glasses are similar, obscuring any structural basis for the glass transition. To delineate structural differences between them, we characterized the atomic structures using the integrated radial distribution functions (RDF) from molecular dynamics (MD) simulations for several metallic liquids and glasses: Cu46Zr54, Ni80Al20, Ni33.3Zr66.7, and Pd82Si18. We find that the integrated RDF leads to cumulative coordination numbers (CN) that are similar for all four metallic glasses and for all four liquids, but are consistently different between the liquid and glass phases. We find that metallic liquids have a fractal dimension of df = 2.54 ± 0.06 from the center atom to the first coordination shell whereas the metallic glasses have df = 2.66 ± 0.04, which suggests the development of weak ordering during the glass transition. Beyond the second coordination shell, the CN indicates a dimension of d = 3 as for a crystal. Crossovers in dimension from df~2.54-2.66 to d = 3 between the first and second coordination shells imply an underlying percolation structure in metallic liquids and glasses.