The effect of zinc and titanium on the structure of calcium–sodium phosphate based glass

An array of different structural probes has been used to define the effect of adding Zn and Ti to a sodium–calcium phosphate glass. X-ray absorption spectroscopy at the Zn K-edge suggests that the Zn atoms occupy mixed (4- and 6-fold) sites within the glass matrix. X-ray diffraction reveals a feature at 2.03 Å that develops with the addition of Zn and Ti and is consistent with Zn–O and Ti–O near-neighbour distances. Neutron diffraction is used to resolve two distinct P–O distances and highlights the decrease in P···P coordination number from 2.0 to 1.7 as the Ti metal concentration rises, which is attributed to the O/P fraction moving away from the metaphosphate value of 3.0 to 3.1 with the addition of Ti. Other correlations, such as those associated with CaOx and NaOx polyhedra, remain largely unaffected. These results suggest that the network forming P···P correlation is most disrupted, with the disorder parameter rising from 0.07 to 0.10 Å with the additional modifiers. Zn appears to be introduced into the network as a direct replacement for Ca and causes no structural variation over the composition range studied.