Raman studies of sol-gel alumina: Finite-size effects in nanocrystalline AlO(OH)

C. J. Doss, R. Zallen
1993 Physical Review B (Condensed Matter)  
A systematic Raman-scattering investigation has been carried out on sol-gel alumina prepared by the hot-water hydrolysis and condensation of Al(OC4H9)3, the Yoldas process, as a function of process variables such as the time spent in the sol phase. Nanocrystalline boehmite, y-A1O(OH), is the principal component of these materials. We have found small but systematic changes, as a function of sol aging time, in the line shape and position of the dominant boehmite Raman band observed in the
more » ... hydrogels. These spectral changes are interpreted in terms of nanocrystallinity-induced finite-size effects associated with the slow growth of A10(OH) nanocrystals in the sol. X-ray-diffraction experiments were used to determine nanocrystal sizes (as small as 3 nm for gels prepared from fresh sols) and to estimate growth kinetics from the Raman-line-shape results. The Raman peak-position shift is proportional to I. , where I. is the average nanocrystal size and a is a Raman-versus-size scaling exponent. For AlO(OH) we And n to be 1.0, close to the scaling-exponent values reported for graphite and boron nitride (BN) and different from the values (about 1.5) that describe the reported behavior of Si and GaAs.
doi:10.1103/physrevb.48.15626 pmid:10008113 fatcat:ogybujmdwnbvhon2btnl636ba4