Advanced physical characterisation of the structural evolution of amorphous (TiO2) x (SiO2)1−x sol-gel materials

Amorphous (TiO2)(x)(SiO2)(1-x) (x = 0.08, 0.18, and 0.41) sol-gel formed materials have been characterised by a combination of X-ray and neutron diffraction, infra-red and Si-29 and O-17 magic angle spinning NMR spectroscopy. This combination allows new insight into the fundamental structural role titanium additions play in silica, entering the network at x = 0.08 but largely phase separating at x = 0.41. At an intermediate value of x = 0.18 there is complex coordination behaviour with initially some Ti-O-Ti linkages forming and both TiO4 and TiO6 coordinations present. It appears that at 500degreesC for the x = 0.18 sample all titanium is present in Ti-O-Si linkages but that this situation is unstable on further calcination. The new information presented here is amalgamated with that from our previous EXAFS, XANES and SAXS on the same samples to produce the most complete view to date of the local and mesoscopic structural behaviour of the (TiO2)(x)(SiO2)(1-x) system produced by the sol-gel method.