Structural evolution in Au- and Pd-based metallic glass forming liquids and the case for improved molecular dynamics force fields

The results of a combined experimental and computational investigation of the structural evolution of Au81Si19, Pd82Si18, and Pd77Cu6Si17 metallic glass forming liquids are presented. Electrostatically levitated metallic liquids are prepared, and synchrotron x-ray scattering studies are combined with embedded atom method molecular dynamics simulations to probe the distribution of relevant structural units. Metal-metalloid based metallic glass forming systems are an extremely important class of materials with varied glass forming ability and mechanical processibility. High quality experimental x-ray scattering data are in poor agreement with the data from the molecular dynamics simulations, demonstrating the need for improved interatomic potentials. The first peak in the x-ray static structure factor in Pd77Cu6Si17 displays evidence for a Curie-Weiss type behavior but also a peak in the effective Curie temperature. A proposed order parameter distinguishing glass forming ability, 1/ST,q1-1, shows a peak in the effective Curie temperature near a crossover temperature established by the behavior of the viscosity, TA.