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Positron annihilation lifetime spectroscopy is employed to measure the size of the interstitial void spaces characterizing the structure of a set of permanently densified ${\mathrm{SiO}}_{2}$ glasses. The average volume of the voids is markedly affected by the densification process and linearly shrinks by almost an order of magnitude after a relative density variation of 22%. In addition, x-ray diffraction shows that this change of density does not modify appreciably the short range order, which remains organized in ${\mathrm{SiO}}_{4}$ tetrahedra. These results strongly suggest a porous medium description for $v\text{\ensuremath{-}}{\mathrm{SiO}}_{2}$ glasses where the compressibility and the medium range order are dominated by the density variation of the voids volume up to densities close to that of $\ensuremath{\alpha}$-quartz.

Neutron diffraction and light scattering studies have been performed on a network glass subject to structural modifications. Large changes of the first sharp diffraction peak (FSDP) and the low frequency dynamics (the boson peak) are demonstrated by gradually changing the intermediate range structural ordering, the short range order being preserved. A recently suggested «universal» correlation for glasses between the positions of the FSDP and the boson peak is shown to fail; in fact opposite trends are observed

We determined the crossover frequency ${\mathrm{\ensuremath{\omega}}}_{\mathrm{co}}$ between phonon and fracton regimes from the study of the low-frequency inelastic light scattering in superionic borate glasses of the type (AgI${)}_{\mathit{x}}$(${\mathrm{Ag}}_{2}$O\ensuremath{\cdot}${\mathrm{B}}_{2}$${\mathrm{O}}_{3}$${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$. The scaling of ${\mathrm{\ensuremath{\omega}}}_{\mathrm{co}}$ with the fractal characteristic length was studied by variation of the AgI concentration x. We thus obtained the diffusion coefficient scaling exponent theta and the spectral dimensionality d\ifmmode \tilde{}\else \~{}\fi{} which characterizes energy diffusion on a fractal.