Abstract
We report multi-nuclear (Na-23 and O-17) solid-state NMR [MAS and triple quantum (3Q) MAS] spectra for sodium tetrasilicate glasses (NS4) quenched from melts at high pressure up to 8GPa. The results show clear evidence for the pressure-induced structural changes in the glasses, forming oxygen linking Si-[4] and Si-[5,Si-6] (Si-[4]-O-Si-[5,Si-6]) with increasing pressure. Whereas the general trend in the effect of pressure is consistent with that of sodium trisilicate glasses (NS3), detailed pressure-induced structural changes for NS4 are largely different from NS3. These differences include the larger fraction of Si-[4]-O-Si-[5,Si-6] and smaller fraction of Na-O-Si-[5,Si-6] for NS4 than NS3 at isobaric conditions. Topological disorder due to Si-O bond length distribution in Si-[4]-O-Si-[4] is also larger for more polymerized NS4 than that for NS3, demonstrating the complexity in structural rearrangement with pressure in silicate glasses and melts with composition at elevated pressure.