Structure of P2O5–SiO2 Pure Network Former Glasses Studied by Solid State NMR Spectroscopy

Abstract

The structure of binary (SiO2)100-x–(P2O5)x glasses has been investigated by Raman scattering, 29Si and 31P magic angle spinning (MAS) as well as static 31P NMR spectroscopy. 29Si chemical shift trends reflect the successive replacement of Si–O–Si by Si–O–P linkages as the compositional parameter x is increased. While 31P MAS NMR does not resolve separate phosphate species, the static 31P NMR lineshapes were successfully simulated by considering the effect of uncorrelated distribution functions of the chemical shift tensor components upon the line shape. On the basis of these simulations, which were also found to be consistent with the experimental 31P MAS NMR spectra, two distinct sites can be resolved: a dominant site characterized by an axially symmetric chemical shift tensor, assigned to P(3) units, and (only in the case of the x = 25 and 30 glasses) a Gaussian component reflecting phosphate species interacting with five- and six-coordinated silicon species. For 0 ≤ x < 25, the decrease in average coo...