Effect of fluorine and nitrogen on the chemical durability of lithium phosphate glasses

The dissolution of glasses belonging to the systems of composition xLi2O·(100 − x)P2O5 (x = 38-55 mol%) and (55 − x / 2)Li2O·xLiF·(45 − x / 2)P2O5 (x = 10-30 mol%), with and without nitrogen, has been studied through immersion of the samples in water at 95 °C using a Soxhlet extractor. In this work, a wide range of compositions prepared by melting has allowed a detailed study of the effect of nitrogen and fluorine in the chemical properties of glasses with variable lithium contents. In lithium phosphorus oxynitride glasses, it was demonstrated that low lithium and high nitrogen contents improve the chemical durability. However, there is a maximum of nitrogen percentage from which the durability is not further improved. In lithium phosphorus fluoro-oxynitride glasses, fluorine introduction leads to a deterioration of the phosphate glasses; however, the introduction of nitrogen in these glasses increases significantly the chemical durability. The structural changes obtained by NMR and XPS are used to explain the effect of lithium, fluorine and nitrogen on the chemical properties. In general, the decrease of non-bridging oxygens and the increase percentage of phosphorus groups with nitrogen increase the chemical resistance.