Complete identification of alkali sites in ion conducting lithium silicate glasses: a computer study of ion dynamics

TL;DR

This study introduces a simple algorithm to identify ionic sites in lithium silicate glasses from long-term trajectories, revealing that the number of sites closely matches the ion count and enabling detailed analysis of ion dynamics.

Contribution

A novel cluster analysis algorithm for identifying ionic sites in disordered conductors from trajectory data, applicable to lithium silicate glasses.

Findings

Number of ionic sites is slightly larger than the number of ions.

Supports a vacancy-based model for ion dynamics.

Allows detailed analysis of ion jump correlations.

Abstract

The available sites for ions in a typical disordered ionic conductor are determined. For this purpose we devised a straightforward algorithm which via cluster analysis identifies these sites from long time ionic trajectories below the glass transition. This is exemplified for a lithium silicate glass (Li_2O)_x (SiO_2)_(1-x) for x = 0.5 and x = 0.1. We find for both concentrations that the number of sites is only slightly bigger than the number of ions. This result suggests a theoretical description of the dynamics in terms of mobile vacancies as most appropriate. Furthermore identification of the ionic sites allows one to obtain detailed characteristics of the ionic motion, e.g. quantification of correlated forward-backward jumps.