A UNIFIED MODEL FOR THE LOW-ENERGY VIBRATIONAL BEHAVIOR OF AMORPHOUS SOLIDS

The anomalous low-energy vibrational behaviour exhibited by amorphous solids (a peak in the vibrational density of states, in C(v)/T3 and in the Raman spectrum-the boson peak-and a plateau in the thermal conductivity) is ascribed to the phonon scattering caused by intrinsic density fluctuation domains in the structure, within which short- and medium-range order is maintained and beyond which the material is structurally isotropic and homogeneous. Phonon localization occurs when the mean-free path is comparable to the size of the domains. This model can also explain the correlation between thc boson-peak frequency and the position of the first sharp diffraction peak in the structure factor observed in a number of inorganic and polymeric amorphous solids.