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

One-dimensional heteronuclear correlation solid-state nuclear magnetic reso nance (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 Q(2) (metaphosphate composition), Q(2) an d Q(1) (between meta- and pyrophosphate compositions), and Q(3) and Q(2) (u ltraphosphate region) have been investigated, Na-23 --> P-31 cross-polariza tion magic-angle-spinning (CPMAS) NMR detects direct interactions between d istinct phosphorus sites and sodium nuclei in the second coordination spher e. Variable-contact CPMAS experiments provide additional information about association of Na-23 nuclei with specific phosphate sites. Time constants d escribing the transfer of magnetization from sodium to phosphorus nuclei ar e found to be affected by sodium ion concentration in ultraphosphate glasse s, and an important finding of these investigations is the degree of correl ation of sodium ions with Q(3) sites in ultraphosphate glasses. (C) 2000 El sevier Science B.V. All rights reserved.