Nucleation and Crystallization of Titania Nanoparticles in Silica Titania Planar Waveguides: a Study by Low Frequency Raman Scattering

SiO2 (1-x) - TiO2 (x) waveguides, with the mole fraction x in the range 0.07-0.20 and thickness of about 0.4 *mm, were deposited on silica substrates by a dip-coating technique. The thermal treatments at 700-900DGC, used to fully densify the xerogels, produce nucleation of TiO2 nanocrystals even for...

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Veröffentlicht in:Materials science forum 2004-01, Vol.455-456, p.520-526
Hauptverfasser: Ferrari, Maurizio, Visintainer, F., Gonçalves, R.R., Ribeiro, Sidney José Lima, Zampedri, L., Almeida, Rui M., Montagna, M., Moser, Enrico, Ivanda, Mile, Martucci, A., Chiasera, A., Guglielmi, M.
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Sprache:eng
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Zusammenfassung:SiO2 (1-x) - TiO2 (x) waveguides, with the mole fraction x in the range 0.07-0.20 and thickness of about 0.4 *mm, were deposited on silica substrates by a dip-coating technique. The thermal treatments at 700-900DGC, used to fully densify the xerogels, produce nucleation of TiO2 nanocrystals even for the lowest TiO2 content. The nucleation of TiO2 nanocrystals and their growth by thermal annealing up to 1300DGC were studied by waveguide Raman spectroscopy, for the SiO2 (0.8)-TiO2 (0.2) composition. By increasing the annealing temperature, the Raman spectrum evolves from that typical of the silica-titania glass to that of anatase, but brookite phase is dominant at intermediate temperatures. In the low frequency region (5-50 cm-1) of the Raman spectra, acoustic vibrations of the nanocrystals are observed. From the measured line shapes, we can deduce the size distribution of the particles. The results are compared with those obtained from the line widths in the X-ray diffraction patterns. Nanocrystals with a mean size in the range 4-20 nm are obtained, by thermal annealing in a corresponding range of 800-1300DGC.
ISSN:0255-5476
1662-9752
1662-9752
DOI:10.4028/www.scientific.net/MSF.455-456.520