Contributions to the mixed-alkali effect in molecular dynamics simulations of alkali silicate glasses

TL;DR

This paper uses molecular dynamics simulations to analyze the mixed-alkali effect in silicate glasses, revealing how ion size and site accessibility influence ion dynamics and cooperative behavior.

Contribution

It introduces a detailed simulation-based analysis of the mixed-alkali effect, highlighting the roles of site stability, residence times, and ion correlations in cation dynamics.

Findings

Longer residence times cause the slowdown.

Foreign site accessibility limits ion mobility.

Correlated jumps indicate cooperative behavior.

Abstract

The mixed-alkali effect on the cation dynamics in silicate glasses is analyzed via molecular dynamics simulations. Observations suggest a description of the dynamics in terms of stable sites mostly specific to one ionic species. As main contributions to the mixed--alkali slowdown longer residence times and an increased probability of correlated backjumps are identified. The slowdown is related to the limited accessibility of foreign sites. The mismatch experienced in a foreign site is stronger and more retarding for the larger ions, the smaller ions can be temporarily accommodated. Also correlations between unlike as well as like cations are demonstrated that support cooperative behavior.