On the interplay of liquid-like and stress-driven dynamics in a metallic glass former observed by temperature scanning XPCS

TL;DR

This study uses advanced temperature scanning XPCS to explore atomic dynamics in a metallic glass, revealing the coexistence of liquid-like and stress-driven motions across the glass transition, extending understanding of relaxation processes.

Contribution

It introduces a novel interpretation of atomic motions in metallic glasses as a superposition of heterogeneous liquid-like and stress-driven ballistic dynamics, extending the dynamical range of XPCS.

Findings

Alpha-relaxation persists in the glass but is masked by faster atomic motions.

Superposition of heterogeneous liquid-like and stress-driven dynamics explains observed behaviors.

Extended dynamical range clarifies the fate of alpha-relaxation across the glass transition.

Abstract

Modern detector technology and highly brilliant fourth-generation synchrotrons allow to improve the temporal resolution in time-resolved diffraction studies. Profiting from this, we applied temperature scanning X-ray photon correlation spectroscopy (XPCS) to probe the dynamics of a Pt-based metallic glass former in the glass, glass transition region, and supercooled liquid, covering up to six orders of magnitude in time scales. Our data demonstrates that the structural alpha-relaxation process is still observable in the glass, although it is partially masked by a faster source of decorrelation observed at atomic scale. We present an approach that interprets these findings as the superposition of heterogeneous liquid-like and stress-driven ballistic-like atomic motions. This work not only extends the dynamical range probed by standard isothermal XPCS, but also clarifies the fate of the alpha-relaxation across the glass transition and provides a new perception on the anomalous, compressed temporal decay of the density-density correlation functions observed in metallic glasses and many out-of-equilibrium soft materials.