Brillouin-scattering measurements of phonon-fracton crossover in silica aerogels

Abstract

Brillouin scattering on porous silica aerogels reveals the onset of the phonon-to-fracton crossover in both the wave-vector and density dependence of the spectra. The results are consistent with a fractal description, giving both the fractal dimension D and the spectral dimension d. In the hypothesis that the samples form single infinite clusters, the numerical values suggest that scalar elasticity is significant in these materials. © 1987 The American Physical Society.