P-31 NMR in (100-x)(NaPO3)-xZnO glasses

P-31 solid State magic angle spinning and liquid nuclear magnetic resonance spectroscopies have been used to investigate the phosphate network of (100 - x)(NaPO3)-xZnO glasses, with 0 < x < 33.3. Addition of ZnO results in the decondensation of the sodium metaphosphate chains: the fraction of Q(2) sites decreases along with the formation of Q(1) sites. Q(1) sites corresponds to chain-end and pyrophosphate groups. The analysis of P-31 chemical shifts leads to the conclusion that Zn2+ ions are bonded only to Q(1) sites, not to Q(2) sites. Some Q(0) sites are present in the glass containing 33.3% ZnO, and are formed by the disproportionation reaction: 2Q(1) = Q(0) + Q(2). Zn2+ coordination was evaluated from Co2+ Visible absorption spectroscopy, assuming that Co2+ and Zn2+ coordinations are similar. In (100 - x)(NaPO3)-xZnO glasses, Zn2+ is mainly octahedral whatever the x value, but the average coordination decreases as x increases. Tetrahedral Zn2+ ions induce a higher shielding, detected by magic angle spinning nuclear magnetic resonance, on the phosphorus of the Q(1) sites to which they are bonded, The tetrahedral Zn2+ amount increases in the glass with x = 33.3%, probably because of the formation of orthophosphate groups. (C) 1997 Elsevier Science B.V.