Molybdenum Influence on the Mixed-Alkali Effect of Lithium–Sodium Phosphate Glasses

In this work, we investigated the mixed-alkali effect (MAE) in molybdophosphate glasses of general composition xNa2O–(40 – x)­Li2O–yMoO3–(60 – y)­P2O5, where 0 ≤ x ≤ 40 and 20 ≤ y ≤ 40. MAE was assessed in terms of the glass-transition temperature (T g) and electrical conductivity of the prepared samples. New insights concerning the influence of molybdenum on MAE are provided herein. In particular, it was observed by differential scanning calorimetry that the addition of molybdenum decreased MAE magnitude for T g. This behavior seems to be related to the formation of better connected and stronger networks when molybdenum oxide (MoO3) was incorporated into the phosphate glasses. Moreover, it was demonstrated that the addition of MoO3 increases the overall electrical conductivity of the glasses, mainly due to the increase of the density of mobile atoms, with no clear influence on MAE. This work provides a deeper understanding regarding the structure of molybdophosphate glasses in terms of both the formation of Mo clusters and random distribution of cations in the glass network. These observations could be related to the variation of MAE.