THE ROLE OF TITANIUM IN TIO2-SIO2 MIXED SOL-GELS - AN X-RAY AND NEUTRON-DIFFRACTION STUDY

Conventional transmission and shallow-angle x-ray diffraction, togethe r with complementary high real-space resolution neutron diffraction da ta, are used to reveal details of the effect of adding titania to a si lica-based sol-gel. A direct observation of the Ti-O correlation has b een possible. At Ti contents low enough to ensure atomic homogeneity, the data are consistent with the fourfold oxygen coordination around t he metal site derived from NMR spectra. Even at these low concentratio ns the nature of the silica network is shown to have been affected sig nificantly, with bondlength distributions being narrowed, and with an increased level of Si-OH indicating a qualitative change in the mesosc opic structure associated with interfacial surfaces. Data from a sampl e having a Ti content high enough to bring about phase separation is a lso presented. The shallow-angle-of-incidence x-ray diffraction method is used to provide information on the differences in structure betwee n 'bulk' materials and those deposited as spun thin films; the data su ggest an increased level of disorder in the thin films.