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

TL;DR

This study uses molecular dynamics simulations to explore how atomic mobility and local structures in a Cu-Zr metallic glass-forming liquid evolve with supercooling, revealing clustering of slow atoms and increased icosahedral order.

Contribution

It provides detailed insights into the relationship between dynamical heterogeneities and local structural features in a binary metallic glass-forming liquid during supercooling.

Findings

Slow atom clusters grow and become more pronounced with cooling.

Zr-enriched regions correlate with slow dynamics.

Increased icosahedral order among Cu atoms in slow regions.

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.