We report Raman scattering from the boehmite,γ-, δ- andα-phases of the alumina gel. Samples are characterized by transmission and scanning electron microscopy, X-ray diffraction and density measurements. The main Raman line in the boehmite phase is red-shifted as well as asymmetrically broadened with respect to that in the crystalline boehmite, signifying the nanocrystalline nature of the gel. Raman signatures are absent in theγ- andδ-phases due to the disorder in cation vacancies. We also show that low frequency Raman scattering from the boehmite phase resembles that from a fractal network, characterized in terms of fraction dimension\(\tilde d\). Taking Hausdorff dimension D of the boehmite gel to be 2.5 (or 3.0), the value of\(\tilde d\) is 1.33±0.02 (or 1.44±0.02), which is close to the theoretically predicted value of 4/3.
KeywordsAl-gel boehmite disordered material fractals phonons fractons
PACS Nos64.60 78.30 63.50
Unable to display preview. Download preview PDF.
- B E Yoldas,Am. Ceram. Soc. Bull. 54, 286 (1975)Google Scholar
- R W G Wyckoff,Crystal structures (Interscience Publishers, Inc., New York, 1948) vol 2Google Scholar
- B E Warren,X-ray diffraction (Addison-Wesley, Reading, MA, 1969) pp. 253 and 258Google Scholar
- aH P Klug and L E Alexander,X-ray diffraction procedures for polycrystalline and amorphous materials (Wiley, New York, 1973) pp. 687 and 635Google Scholar
- Powder diffraction file (International Centre for Diffraction Data, 1990) 10–173Google Scholar
- A B Kiss, G Keresztury and L Farkas,Spectrochim. Acta A36, 653 (1980)Google Scholar
- P M Fauchet and I H Campbell,Critical review in solid state and materials sciences 14, S79 (1988)Google Scholar
- S Alexander and R Orbach,J. Phys. Lett. (Paris) 43, L625 (1982)Google Scholar