Role of titanium in TiO2 : SiO2 sol–gels: an X-ray diffraction study

Transmission X-ray diffraction has been used to study a series of powdered silica:titania sol-gel glasses with titania contents ranging from a 'pure' silica sample through to high titania levels where phase separation is predicted to occur. Analysis of the data reveals a change in second- and: third-neighbour coordination numbers with increasing Ti content and confirms that for low titanium contents the sol-gels are atomically mixed. The lower titanium content sol-gels have also been studied as spun thin films using shallow-angle X-ray diffraction. Comparison with the transmission studies shows an increase in disorder in the silica network when the material is in the form of a coating rather than in the bulk. An increase in the nun;ber of Si-O-H bonds is also suggested.