Résumé
Brillouin and low frequency Raman scattering experiments have been performed on series of B2O3 - x M2O glasses where M = Li, Na, K, Rb, Cs, Tl. The concentration and composition dependences of the velocity and attenuation of longitudinal and transversal acoustic waves have been measured, as well as those of the Raman "boson" peak. The composition and concentration dependence of the acoustic velocity seems to result from two competitive effects : the first one is related to the transition of boron atoms from three - to four coordination with increasing x and the second one to the structural changes connected to the sterical hinderance of the M+ cations. The maximum frequency of the boson peak has a behaviour similar to that of sound velocity. This similarity can be understood on the basis of the continuum theory of low-frequency Raman spectrum.