Structural Role of Water in a Sodium Phosphate Glass by Neutron Diffraction

Abstract

Neutron diffraction with isotopic H/D-substitution was used to study the network-modifying effect of water in a H2O-Na2O-2P2O5 glass. The resolved fractions of P−OT and P−OB bonds and the O−O coordination number indicate similarity to the specifics of a metaphosphate structure. Thus, oxygen of H2O added ruptures a P−O−P bridge, increasing the number of terminal oxygens. The combined analysis of the first-neighbour peaks in the correlation functions of the hydrogenated and deuterated samples yields H−O distances of 0.101 and 0.157 nm and H−P distances of 0.223 and 0.250 nm. Such distances are well explained with the formation of O−H· · ·O hydrogen bridges. The corresponding O−O distances superpose with the edge lengths of the PO4 tetrahedra. Significant fractions of short H−H distances typical of water molecules (0.155 nm) or clustering of hydrogen bridges are not detected. The Na−O coordination number of five is similar to that found for the NaPO3 glass.