Temperature dependence of fast relaxation processes in amorphous materials

TL;DR

This study models how temperature influences relaxation dynamics in amorphous materials, revealing a transition from faster-than-exponential to exponential relaxation with increasing temperature, aligning with experimental observations.

Contribution

Introduces a 3D mesoscopic model combining elastic interactions and thermal activation to explain relaxation behavior in glasses, including crossover phenomena and heterogeneity.

Findings

Relaxation becomes faster-than-exponential at low temperatures.

A crossover to exponential relaxation occurs as temperature increases.

Waiting times between activations are broadly distributed at low temperatures.

Abstract

We examine the structural relaxation of glassy materials at finite temperatures, considering the effect of activated rearrangements and long-range elastic interactions. Our three-dimensional mesoscopic relaxation model shows how the displacements induced by localized relaxation events can result in faster-than-exponential relaxation. Thermal activation allows for local rearrangements, which generate elastic responses and possibly cascades of new relaxation events. To study the interplay between this elastically-dominated and thermally-dominated dynamics, we introduce tracer particles that follow the displacement field induced by the local relaxation events and also incorporate Brownian motion. Our results reveal that the dynamic exponents and shape parameter of the dynamical structure factor depend on this competition and display a crossover from faster-than-exponential to exponential relaxation as temperature increases, consistent with recent observations in metallic glasses. Additionally, we find the distribution of waiting times between activations to be broadly distributed at low temperatures, providing a measure of dynamical heterogeneities characteristic for to glassy dynamics.