Dynamical, structural and chemical heterogeneities in a binary metallic glass-forming liquid

Abstract

As approaching the glass transition, particle motion in liquids becomes highly heterogeneous and regions with virtually no mobility coexist with liquid-like domains. This complex dynamics is believed to be responsible for different phenomena including non-exponential relaxation and the breakdown of Stokes-Einstein relation. Understanding the relationships between dynamical heterogeneities and local structure in metallic liquids and glasses is a major scientific challenge. Here we use classical molecular dynamics simulations to study the atomic dynamics and microscopic structure of $\mbox{Cu}_{50}\mbox{Zr}_{50}$ alloy in the supercooling regime. Dynamical heterogeneities are identified via an isoconfigurational analysis. As deeper supercooling is achieved a transition from isolated to clustering low mobility atoms is reported. These slow clusters, whose size grow upon cooling, are also associated to concentration fluctuations, characterized by a Zr-enriched phase, with a composition $\mbox{CuZr}_2$. In addition, a structural analysis of slow clusters based on Voronoi tessellation evidences an increase with respect of the bulk system of the fraction of Cu atoms having a local icosahedral order. These results are in agreement with the consolidated scenario of the relevant role played by icosahedral order in the dynamic slowing-down in supercooled metal alloys.