Mixed alkali effect in Li and Na aluminophosphate glasses: influence of the cation environment

This paper deals with the variation of the mixed alkali effect (MAE) in Li and Na aluminophosphate glasses. The general system investigated is: 0.46 [xNa2O(1−x)Li2O], 0.54 [yAl2O3(1−y)P2O5], with x varying between 0 and 1 to probe the MAE, and y between 0 and 0.08 to modify the cation environment and to try to understand how the amorphous host affects the ionic motions. We show that the dc conductivity minimum characteristic of the MAE effect decreases and almost disappears as Al2O3 is added to mixed phosphate glasses. On another hand, the dc conductivity of the single alkali glasses is almost not affected by Al2O3 addition. Dielectric relaxation characteristics also change with the Al2O3 concentration in mixed glasses and not in single ones. On another hand, the mixed alkali peak measured using mechanical relaxation appears to be almost not affected by the presence of Al2O3. This decoupling between the mechanical and dielectric relaxation processes appears to «through into question» the proposal that the mechanical relaxation in mixed alkali glasses accounts for sites reconfiguration to adapt to the different cations.