Real-space atomic dynamics in metallic liquids investigated by inelastic neutron scattering

Understanding the dynamics of liquids at the atomic level remains a major challenge. Even though viscosity is one of the most fundamental properties of liquids, its atomistic origin is not fully elucidated. Through inelastic neutron scattering experiment on levitated metallic liquid droplets, the time-dependent pair correlation function, the Van Hove function, was determined for Zr50Cu50 and Zr80Pt20 liquids at various temperatures. The time for change in local atomic connectivity, tau LC, which is the timescale of atomic bond cutting and forming, is estimated based on the exponential decay of the nearest neighbor peak of the Van Hove function. At high temperatures above the crossover temperature TA, tau LC is equal to the Maxwell relaxation time, tau M = eta/G infinity, where eta is the macroscopic shear viscosity and G infinity is the high-frequency shear modulus. Below TA the ratio of tau M/tau LC increases with decreasing temperature, indicating increased atomic cooperativity as predicted by molecular dynamics simulation.