On the scattering mechanisms responsible for the Boson peak in glasses

A well-resolved Boson peak has been observed in the Raman spectra of sulphi de and sulphurhalide glasses and its temperature dependence is studied in t he range 20-300 K. The variation of the spectral profile of the Boson peak with temperature, which is manifested by a non-monotonic variation of slope at the low energy side of the peak and a continuously increasing asymmetry of the peak with decreasing temperature, suggests the presence of two vibr ational scattering components which vary in different ways with temperature . The existence of two such contributions is discussed in terms of a qualit ative model which assumes an asymmetrical double well potential of vibratio nal states. A decrease of the crossover frequency od (defined by the low an d high energy slopes of the Boson peak) with decreasing temperature is in a greement with the theory of the soft potential model for which an increase of the relative population of non-interacting to interacting harmonic oscil lators is expected with decreasing temperature. (C) 1999 Elsevier Science L td. All rights reserved.