In situ Anti-Stokes Raman Monitoring of Gel-to-Anatase Phase Transformation of Titania

Abstract

The phase transformation from a gel of titanium alkoxide to crystalline anatase was observed in situ by anti-Stokes Raman scattering. Utilization of anti-Stokes scattering eliminates interference from the fluorescence of decomposing organic residuals during the pyrolysis process. The anti-Stokes Raman spectra suggest a highly disordered structure during the pyrolysis process. The structure of the titania gel, which is characterized by broad Raman peaks around 440 and 620 cm⁻¹, was transformed into the amorphous structure by increasing the temperature up to 200–300 °C. This amorphous structure is supported by a flat Raman spectrum lacking specific features in the wavenumber region from 200 to 1000 cm⁻¹. A partially crystallized gel also exhibits the further progress of amorphization during the pyrolysis process, which is explained by the disordering of the local structure of the gel due to the generation of pyrolyzed organic species.