Sound wave scattering in network glasses.

The acoustic branch of two network glasses, (Li2O)xB2O3 ( x = 0.25 and 0.5), is followed over a large momentum transfer range 1-12 nm(-1), using inelastic x-ray scattering. We observe the transition from propagating modes to a region of strong scattering as the Ioffe-Regel limit is reached. A region of Rayleigh scattering of the acoustic modes precedes the strong scattering regime at larger Q, causing a rapid decrease of the mean-free path of the modes.