New insights into medium-range order around titanium in sol–gel derived silica through isotope difference neutron diffraction and reverse Monte Carlo modelling

Neutron diffraction with isotopic titanium substitution allows the nature of the cation sites to be determined beyond nearest-neighbor distances for the first time in a sol–gel derived titania–silica glass. Reverse Monte Carlo (RMC) modelling of the results shows unequivocally that titanium substitutes for silicon within the homogeneous glass network, existing mostly as TiO4, with a minority TiO6 component. The fundamental scientific interest, and wide-ranging technologically significant properties of titania additions to silica, demand an understanding of the precise nature of the titanium site.