Structural properties of sodium phosphate glasses from 23Na → 31P cross-polarization NMR

Abstract One-dimensional heteronuclear correlation solid-state nuclear magnetic resonance (NMR) experiments are utilized to determine local structural changes in sodium phosphate glass compositions with ratios of Na/P of 0.25, 0.78, 1 and 1.3. Glasses containing only Q2 (metaphosphate composition), Q2 and Q1 (between meta- and pyrophosphate compositions), and Q3 and Q2 (ultraphosphate region) have been investigated. 23Na → 31P cross-polarization magic-angle-spinning (CPMAS) NMR detects direct interactions between distinct phosphorus sites and sodium nuclei in the second coordination sphere. Variable-contact CPMAS experiments provide additional information about association of 23Na nuclei with specific phosphate sites. Time constants describing the transfer of magnetization from sodium to phosphorus nuclei are found to be affected by sodium ion concentration in ultraphosphate glasses, and an important finding of these investigations is the degree of correlation of sodium ions with Q3 sites in ultraphosphate glasses.