Mixed alkali effect in glasses.

We have applied the bond-valence technique to reverse Monte Carlo produced structural models of mixed alkali phosphate glasses in order to elucidate the mixed alkali effect (MAE) in glasses. For the first time, the MAE is reproduced and understood directly from structural models in quantitative agreement with available experimental results. The two types of alkali ions are randomly mixed and have distinctly different conduction pathways of low dimensionality. This implies that A ions tend to block the pathways for the B ions and vice versa, and this is the main reason for the MAE.