B. Rufflé

Indentation deformation mechanism in glass: Densification versus shear flow

Although the characteristic time constant for viscous relaxation of glass is so large at room temperature that viscous flow would be hardly detectable, a permanent deformation can be easily achieved at ambient temperature by applying a sharp contact loading—a Vickers indenter for instance—for few seconds only. We provide direct evidence for densification and volume conservative shear flow by means of atomic force microscopy topological analysis of the indentation profile and volume on as-quenched and densified specimens (pressure up to 25 GPa). We show that both possible mechanisms contribute to different extents depending on the glass composition. A major finding is that densification predominates in glasses with relatively low atomic packing density but that shear flow relays on once densification is achieved.

Glass-Specific Behavior in the Damping of Acousticlike Vibrations

High frequency sound is observed in lithium diborate glass, Li2O-2B2O3, using Brillouin scattering of light and x rays. The sound attenuation exhibits a nontrivial dependence on the wave vector, with a remarkably rapid increase towards a Ioffe-Regel crossover as the frequency approaches the boson peak from below. An analysis of literature results reveals that the boson-peak frequency is closely related with a Ioffe-Regel limit for sound in many glasses. We conjecture that this relation, specific to glassy materials, might be rather common among them.

Boson Peak and its Relation to Acoustic Attenuation in Glasses

Experimental results on the density of states and on the acoustic modes of glasses in the THz region are compared to the predictions of two categories of models. A recent one, solely based on an elastic instability, does not account for most observations. Good agreement without adjustable parameters is obtained with models including the existence of nonacoustic vibrational modes at THz frequency, providing in many cases a comprehensive picture for a range of glass anomalies.

Hypersound damping in vitreous silica measured by picosecond acoustics

The attenuation of longitudinal acoustic phonons up to frequencies nearing

Revealing the fast atomic motion of network glasses

250\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}

Scaling the temperature-dependent boson peak of vitreous silica with the high-frequency bulk modulus derived from Brillouin scattering data.

is measured in vitreous silica with a picosecond optical technique. By taking advantage of interferences on the probe beam, difficulties encountered in early pioneering experiments are alleviated. Sound damping at

Observation of the onset of strong scattering on high frequency acoustic phonons in densified silica glass.

250\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}

Oxygen behavior in aluminum nitride

and room temperature is consistent with relaxation dominated by anharmonic interactions with the thermal bath, extending optical Brillouin scattering data. Our result is at variance with claims of a recent deep-UV experiment which reported a rapid damping increase beyond

Vitreous silica distends in helium gas: acoustic versus static compressibilities.

100\phantom{\rule{0.3em}{0ex}}\mathrm{GHz}

Temperature Dependence of Single-Crystal Elastic Constants of Flux-Grown α-GaPO4

. A comprehensive picture of the frequency dependence of sound attenuation in