Relationship between Fragility, Diffusive Directions and Energy Barriers in a Supercooled Liquid

TL;DR

This paper explores how the potential energy landscape influences diffusion and relaxation in supercooled liquids, linking fragility and relaxation processes to the landscape's topography and diffusive directions.

Contribution

It demonstrates that diffusion and relaxation behaviors in supercooled liquids can be explained through the density of diffusive directions and energy barriers within the potential energy landscape.

Findings

Beta relaxation is linked to the search for diffusive directions.

Strong liquids exhibit energy-activated diffusion.

Fragile-to-strong crossover involves changes in PEL topography.

Abstract

An analysis of diffusion in a supercooled liquid based solely in the density of diffusive directions and the value of energy barriers shows how the potential energy landscape (PEL) approach is capable of explaining the $\alpha$ and $\beta$ relaxations and the fragility of a glassy system. We find that the $\beta$ relaxation is directly related to the search for diffusive directions. Our analysis shows how in strong liquids diffusion is mainly energy activated, and how in fragile liquids the diffusion is governed by the density of diffusive directions. We describe the fragile-to-strong crossover as a change in the topography of the PEL sampled by the system at a certain crossover temperature $T_\times$.