Backward correlations and dynamic heterogeneities: a computer study of ion dynamics

TL;DR

This study uses computer simulations to analyze ion dynamics in lithium metasilicate, revealing long-range back-dragging effects and temperature-dependent heterogeneities, advancing understanding of ion transport in glassy materials.

Contribution

It introduces three-time correlation functions to analyze ion dynamics, demonstrating long-range back-dragging and heterogeneity effects in lithium ions.

Findings

Back-dragging effect is long-ranged and exceeds nearest neighbors.

Back-dragging fulfills the time-temperature superposition principle.

Dynamic heterogeneities increase with decreasing temperature.

Abstract

We analyse the correlated back and forth dynamics and dynamic heterogeneities, i.e. the presence of fast and slow ions, for a lithium metasilicate system via computer simulations. For this purpose we define, in analogy to previous work in the field of glass transition, appropriate three-time correlation functions. They contain information about the dynamics during two successive time intervals. First we apply them to simple model systems in order to clarify their information content. Afterwards we use this formalism to analyse the lithium trajectories. A strong back-dragging effect is observed, which also fulfills the time-temperature superposition principle. Furthermore, it turns out that the back-dragging effect is long-ranged and exceeds the nearest neighbor position. In contrast, the strength of the dynamic heterogeneities does not fulfill the time-temperature superposition principle. The lower the temperature, the stronger the mobility difference between fast and slow ions. The results are then compared with the simple model systems considered here as well as with some lattice models of ion dynamics.