Published online by Cambridge University Press: 21 February 2011
Amorphous SiO2, TiO2 and x SiO2-(1-x) TiO2 powders, with nominal values of x=0.9, 0.7 and 0.5, havebeen prepared via sol-gel, using silicon tetrahoxysilane (TEOS) and titaniumtetraisopropoxide Ti(OPri)4. X-ray photoelectronspectroscopy (XPS) and X-ray induced Auger electron spectroscopy (XAES) areused for studying the surface chemical structure of the powders as afunction of the air thermal treatment temperature up to 1273 K. For thewhole range of temperature, XPS and XAES signals indicate that silicon andtitanium are present as Si4+ and Ti4+ oxides. From theline shape of the O 1s peak, it is possible to distinguish between thesingle O-Ti and O-Si bonds and to disclose also the presence of Si-O-Ticross linking bonds that are supposed to act as bridges between SiO2 and TiO2 moieties. Starting from 873 K, theSi-O-Ti bonds are broken and formation of a low amount of new Ti-O and ahigher amount of Si-O bonds takes place. Si/Ti atomic ratios obtained bycurve fitting the O Is peaks and from Ti 2p3/2 and Si 2p peaks,confirm the silicon oxide surface enrichment. Furthermore, with increasingtemperature, XAES data indicate the formation of crystalline phases.