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-2P 2O5 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.