Local structure of zinc ultraphosphate glasses containing large amount of hydroxyl groups:: 31P and 1H solid state nuclear magnetic resonance investigation

Zinc ultraphosphate glasses containing variable amounts of hydroxyl groups were prepared by melting phosphoric acid and zinc oxide at 900 degrees C for different times. The H-1-P-31 cross polarization (CP) combined with magic angle spinning (MAS) nuclear magnetic resonance (NMR) at variable contact time show clearly the presence of Q(2) sites including 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, particularly the Q(2)(H) sites. A quantification of the measurements indicates an evolution of the relative fractions of the sites versus the melting 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 those 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 surface. 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 homogeneously distributed in the glass matrix, in good agreement with the analysis of P-31 NMR data. (C) 1998 Elsevier Science B.V.