Pressure-driven structural depolymerization of zinc phosphate glass

Understanding pressure-induced structural transformation in glasses is important for designing more damage resistant compositions, since the contact damage that leads to fracture induces high stress levels. However, although phosphorus oxide is an important component in various glasses of industrial interest, knowledge of the structural response of phosphate-based glasses to high pressure remains very limited. In this study, we investigate the influence of hot isostatic compression on the structure, volume densification, and mechanical properties (hardness, crack resistance, and brittleness) of a zinc phosphate glass with O/P ratio = 3.25. Bulk glasses are compressed up to 2 GPa at the glass transition temperature, enabling permanent densification, in turn leading to an increase in hardness and brittleness and decrease in crack resistance. Using Raman and 31P NMR spectroscopy we find that hot compression results in a non-monotonic change in the phosphate network polymerization degree, which is further accompanied by changes in the bond angles and extent of network disorder. We also show that densification during indentation and hot compression is associated with similar structural changes, suggesting that part of the mechanically applied energy during contact damage will be consumed by the pressure-driven structural changes.