The crossover from propagating to strongly scattered acoustic modes of glasses observed in densified silica

Abstract

Spectroscopic results on low frequency excitations of densified silica are presented and related to characteristic thermal properties of glasses. The end of the longitudinal acoustic branch is marked by a rapid increase of the Brillouin linewidth with the scattering vector. This rapid growth saturates at a crossover frequency Omega_co which nearly coincides with the center of the boson peak. The latter is clearly due to additional optic-like excitations related to nearly rigid SiO_4 librations as indicated by hyper-Raman scattering. Whether the onset of strong scattering is best described by hybridization of acoustic modes with these librations, by their elastic scattering (Rayleigh scattering) on the local excitations, or by soft potentials remains to be settled.

14 pages, 6 figures, to be published in a special issue of J. Phys. Condens. Matter

Cited by in corpus (9)

• Inhomogeneous elastic response of silica glass
• Anharmonic vs. relaxational sound damping in glasses: II. Vitreous silica
• First principles study of a sodium borosilicate glass-former II: The glass state
• Vibrations and Relaxations in a Soft Sphere Glass: Boson Peak and Structure Factors
• Anharmonic vs. relaxational sound damping in glasses: I. Brillouin scattering from densified silica
• Discontinuous shear modulus determines the glass transition temperature
• Vibrational states and disorder in continuously compressed model glasses
• The vibrational density of states of a disordered gel model
• Acoustic damping in Li${}_2$O-2B${}_2$O${}_3$ glass observed by inelastic x-ray and optical Brillouin scattering