P-31 NMR IN (100-X)(NAPO3)-XZNO GLASSES

P-31 solid State magic angle spinning and liquid nuclear magnetic reso nance spectroscopies have been used to investigate the phosphate netwo rk of (100 - x)(NaPO3)-xZnO glasses, with 0 < x < 33.3. Addition of Zn O results in the decondensation of the sodium metaphosphate chains: th e fraction of Q(2) sites decreases along with the formation of Q(1) si tes. Q(1) sites corresponds to chain-end and pyrophosphate groups. The analysis of P-31 chemical shifts leads to the conclusion that Zn2+ io ns are bonded only to Q(1) sites, not to Q(2) sites. Some Q(0) sites a re present in the glass containing 33.3% ZnO, and are formed by the di sproportionation 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 coor dination decreases as x increases. Tetrahedral Zn2+ ions induce a high er shielding, detected by magic angle spinning nuclear magnetic resona nce, 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%, probab ly because of the formation of orthophosphate groups. (C) 1997 Elsevie r Science B.V.