Relationships between fragility and structure through viscosity and high temperature NMR measurements in Li2O-ZnO-P2O5 phosphate glasses

The experimental viscosity data of a series of lithium-zinc metaphosphate glasses of composition xLi2O·(50 − x)ZnO·50P2O5 have been analyzed in order to get new insights into the compositional and structural influence on viscosity in phosphate glasses. The short and intermediate range order structures have been studied by Raman spectroscopy and Nuclear Magnetic Resonance at room temperature and at temperatures above Tg with in situ solid state high temperature Nuclear Magnetic Resonance. The substitution of ZnO by Li2O leads to changes on the short and medium range order structures that are reflected in the glass properties, such as molar volume, glass transition temperature and fragility. It was demonstrated that the fragility increases as a consequence of a weaker and more flexible glass network that makes easier the flow of the rigid structural units through the glass.