THE SHORT-RANGE STRUCTURE OF SODIUM-PHOSPHATE GLASSES .1. MAS NMR-STUDIES

A series of x(Na2O + H2O)·(1 - x)P2O5 glasses have been characterized by 31P and 23Na magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. High-resolution 31P NMR spectra reveal the presence of Q2-(2 bridging oxygen/tetrahedron) and Q3-(3 bridging oxygen/tetrahedron) tetrahedral sites in glasses with x < 0.5, and Q2- and Q1-tetrahedral sites in glasses with x > 0.5. Quantitative measurements of the respective NMR site populations are in excellent agreement with Van Wazer's predictions for the structures of ionic phosphates and illustrate the depolymerizing effects of residual H2O on the glass structure. The systematic change in the Q231P chemical shift is consistent with an increase in the average π-bond character of the phosphorus-nonbridging oxygen bond as x decreases. © 1990.