Channel diffusion in a lithium–potassium metasilicate glass using the isoconfigurational ensemble: Towards a scenario for the mixed alkali effect

• We simulate the dynamics of mobile Li and K ions in mixed metasilicate glasses.
• We used the Molecular Dynamics formalism and the isoconfigurational ensemble method.
• The ionic conducting channels and their environments were re-described in a new way.
• A specific cooperative movement among moving ions appears as highly probable.
• We show that the alkali ion diffusion evolves in specific channels for the ions.

Performing Molecular Dynamic simulations and using the isoconfigurational ensemble method, we studied the effect of the potassium cation replacing the half part of lithium ions in glassy Li2SiO3. This so-constructed glassy system has the main ingredients present in an immediate forthcoming definition of mixed alkali effect (MAE) in glasses. We show the existence of dynamic correlations among the cations of the same species, i.e. Li–Li and K–K, whereas a very weak correlation was observed between a distinct pair of cations. With this novel approach we can put into evidence that the alkali ion diffusion evolves in specific channels for the ions: a Li ion prefers the lithium ion channel and a K ion prefers the potassium ion channel. This result is coincident with previous simulational studies using the bond–valence technique to reverse Monte Carlo and recent experimental findings using quasielastic neutron scattering.