Network Structure and Connectivity in SnO-P2O5 Glasses: Results from 2D 31P and 119Sn NMR Spectroscopy.

The compositional evolution of the network structure and connectivity in binary SnO-P2O5 glasses with 35 ≤ mol % SnO ≤ 55 is studied using two-dimensional 119Sn and 31P NMR spectroscopy. The phosphate Q n species concentrations, as obtained from the analyses of the 31P NMR spectral line shapes suggest that the network modification can be described in terms of a binary Q-speciation model. On the other hand, the 119Sn NMR spectra suggest that the Sn-O coordination environment in these glasses is composition dependent. Sn is present in both 3-fold (trigonal pyramid) and 4-fold (trigonal bipyramid) coordinations with oxygen in these glasses. The relative fraction of the trigonal pyramidal environment increases with increasing SnO content. The unusually low glass transition temperature Tg of these glasses (241-266 °C) is argued to be related to the low coordination number of Sn, leading to a relatively sparsely connected structural network.