Ion transport pathways in molecular dynamics simulated alkali silicate glassy electrolytes

The xM₂O-(1 − x)SiO₂ (M = Li, Na, and K, and 0.1 ≤ x ≤ 0.5) glass systems have been studied by constant volume molecular dynamics (MD) simulations. The bond valence (BV) method is applied to the equilibrated configurations to analyse the structural variation in these glass systems with increasing network modifier content, its consequence for M⁺ ion mobility, as well as the distribution of bridging and non-bridging oxygen atoms and the variation of the Q_i values. The contribution of non-bridging oxygen atoms to the BV sums exhibits a transition around x = 1/3 for Li₂O and Na₂O doped glasses. The observed Q_i variation is consistent with a bond order model. Despite slight deviations of the interatomic distances in the MD-simulated glasses, their BV analysis reveals characteristic features of the ion transport pathway. For complex disordered systems with low ion mobilities the bond valence analysis of the pathway characteristics for the mobile ion is thus a viable method to extract ion transport properties even if the mobilities are too low to be directly analysed from the mean square displacements over the simulated period.