Topological phases of (Na₂O)_x(P₂O₅)_100-x glasses and their molecular structure from Raman scattering.

The observation of both a reversibility window and a fragility window in the 37.5% < x < 46% range of soda in titled glasses from Calorimetric experiments¹ fixes the 3 topological phases. Raman polarization and glass compositional studies show that the feature near 1166 cm^-1 in glasses at x = 50% consists of a triad of modes, a majority symmetric mode of Q² species and two minority “defect modes” due to termination of the Q² bearing long chains by Q¹ like local structures, not only at x > 50% but also at x < 50%. These defects are under-constrained and contribute to an increasing baseline in the non-reversing heat flow term with increasing x. The fractions of Q³,Q² and Q¹ local structures with composition deduced from respective Raman active modes in the 20% < x < 60% range nicely track the usual mean-field behavior, independently deduced from NMR² but with some minor but noticeable differences.

1. C. Mohanty, M.S. Thesis, University of Cincinnati, 2018.
2. Brow, R. K. Review: the structure of simple phosphate glasses. J. Non. Cryst. Solids 263, 1–28 (2000).