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By means of inelastic cold neutron scattering the density of vibrational states (DVS) has been determined for a series of vitreous materials: SOz, As2& and metallic glass MgToZnso.In the low-energy range of the spectrum (E -(2 i 10) meV) for these materials DVS reveals a universal, but non-Debye form. The data obtained are compared to different models. A comparison with the Raman scattering data provides the spectral dependence for the coupling of the light to the vibrational excitations.The most important differences between elementary excitation spectra of crystalline and amorphous materials manifest themselves in the low-energy range. The low-temperature (5" G 1 K) anomalies in specific heat and thermal conductivity of amorphous materials are * * *The authors are indebted to S. POPOV and R. RODIONOVA for the samples provided for.

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Liquid-and solid-like particles in a glass are defined via the Lindemann criterion of melting. Due to structure inhomogeneity the amplitude of the mean-square thermal atomic displacements r 2 varies spatially. This situation defines a percolation problem for liquid-and solid-like clusters. There are two percolation thresholds: the first corresponds to the temperature T1 at which the first infinite cluster of liquid-like particles appears. The second threshold T2 corresponds to a point at which the last infinite cluster of solid-like particles disappears. In the 3D case T1 ≤ Tg ≤ T2 holds. We argue that this interval is relatively broader in strong glass-formers in comparison with fragile ones; this means that the spatial distribution of r 2 and, respectively, of the elastic constants is broader in the former case than in the latter one.Comparison with neutron experimental data on r 2 shows that numerically T1 is close to the Vogel-Fulcher-Tammann temperature T0 and T2 is close to the critical temperature Tc defined within mode coupling theory.