LOCAL-STRUCTURE OF ZINC ULTRAPHOSPHATE GLASSES CONTAINING LARGE AMOUNT OF HYDROXYL-GROUPS - P-31 AND H-1 SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE INVESTIGATION

Zinc ultraphosphate glasses containing variable amounts of hydroxyl gr oups were prepared by melting phosphoric acid and zinc oxide at 900 de grees C for different times. The H-1-P-31 cross polarization (CP) comb ined with magic angle spinning (MAS) nuclear magnetic resonance (NMR) at variable contact time show clearly the presence of Q(2) sites inclu ding those bonded to H+, Q(2)(H), and those bonded to Zn2+, Q(2)(Zn), and Q(3) sites. Moreover, the detailed examination of the line widths reveals that the Q(n) sites are distributed in the glass matrix, parti cularly the Q(2)(H) sites. A quantification of the measurements indica tes an evolution of the relative fractions of the sites versus the mel ting time. H-1 MAS NMR reveals the existence of at least three kind of protons characterized by different isotropic chemical shifts: 17 +/- 0.2, 13 +/- 0.2 and 8.6 +/- 0.2 ppm. These protons are identified as t hose involved, respectively, in Q(2)(H)...Q(2)(Zn) groups, in Q(2)(H). ..Q(2)(H) groups and those of water molecules adsorbed on the glass su rface. The measurements of spin lattice and spin-spin relaxation times indicate that the water molecules are strongly adsorbed and that the protons involved in Q(2)(H)...Q(2)(Zn) and in Q(2)(H)...Q(2)(H) are ho mogeneously distributed in the glass matrix, in good agreement with th e analysis of P-31 NMR data. (C) 1998 Elsevier Science B.V.