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

Abstract

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 Z⁢r50⁢C⁢u50 and Z⁢r80⁢P⁢t20 liquids at various temperatures. The time for change in local atomic connectivity, 𝜏𝐿⁢𝐶, 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, 𝜏𝐿⁢𝐶 is equal to the Maxwell relaxation time, 𝜏𝑀=𝜂/𝐺∞, where η is the macroscopic shear viscosity and 𝐺∞ is the high-frequency shear modulus. Below 𝑇𝐴 the ratio of 𝜏𝑀/𝜏𝐿⁢𝐶 increases with decreasing temperature, indicating increased atomic cooperativity as predicted by molecular dynamics simulation.