Disentangling structural and kinetic components of the {\alpha}-relaxation in supercooled metallic liquids

TL;DR

This study uses synchrotron techniques to explore the microscopic structure-dynamics relationships in supercooled metallic liquids, revealing how structural and kinetic factors influence the alpha-relaxation process and dynamical heterogeneities.

Contribution

It provides the first detailed disentanglement of structural and kinetic contributions to alpha-relaxation in supercooled metallic liquids using advanced synchrotron methods.

Findings

Structural fragility differs between alloys and correlates with density fluctuation decay.

Kinetic fragility is similar across alloys despite structural differences.

Atomic motion reflects both topological and chemical short-range order, affecting relaxation.

Abstract

The particle motion associated to the {\alpha}-relaxation in supercooled liquids is still challenging scientists due to its difficulty to be probed experimentally. By combining synchrotron techniques, we found the existence of microscopic structure-dynamics relationships in Pt42.5Cu27Ni9.5P21 and Pd42.5Cu27Ni9.5P21 liquids which allows us to disentangle structural and kinetic contributions to the {\alpha}-process. While the two alloys show similar kinetic fragilities, their structural fragilities differ and correlate with the temperature dependence of the stretching parameter describing the decay of the density fluctuations. This implies that the evolution of dynamical heterogeneities in supercooled alloys is determined by the rigidity of the melt structure. We find also that the atomic motion not only reflects the topological order but also the chemical short-range order, which can lead to a surprising slowdown of the {\alpha}-process at the mesoscopic length scale. These results will contribute to the comprehension of the glass transition, which is still missing.