Local fivefold symmetry in liquid and undercooled Ni probed by x-ray absorption spectroscopy and computer simulations

Presence and significance of fivefold configurations in liquid metals are investigated by combining x-ray absorption spectroscopy and computer simulations (molecular dynamics and reverse Monte Carlo) in liquid and undercooled liquid nickel. We show that icosahedral short-range ordering (ISRO), probed by common-neighbor (CNA) and spherical invariant (̂ \^W₆) analysis, involves a limited fraction (14--18% in undercooled nickel for different structural models) of local atomic configurations. The emerging picture for the liquid structure is that of a mixture of nearly icosahedral structures embedded in a disordered network mainly composed of fragments of highly distorted icosahedra (40--45% of the total), structures reminiscent of the crystalline phase, and other configurations.