Structural studies during gelation of WO3 investigated by in-situ Raman spectroscopy

In the course of the preparation of WO3 by sol-gel technique we have studie d kinetics of its synthesis and the structural changes during gelation. In- situ Raman scattering spectra were obtained for a series of samples during the transition from aqueous solution to gel. The changes in the Raman featu res were monitored as a function of time during gelation. The removal of wa ter molecules affects the symmetric W=O stretching mode. The Raman spectrum of a gelified sample shows peaks attributed to the O-W-O bending mode and the disappearance of the high-frequency mode attributed to polyanionic spec ies. After two days the gelified sample became a precipitated material, whi ch exhibited the Raman spectrum of a crystalline tungsten oxide hydrate.