DISORDER AND ITS DYNAMICS IN THE GLASS-TRANSITION

In structurally disordered materials there is strong inelastic light scattering in the low-frequency (Raman) region, say omega less-than-or-equal-to 50 cm-1. In glasses, i.e. statically disordered solids, it is ascribed to vibrational excitations, an increased density of states and suppression of momentum conservation. New experimental evidence is cited for an analysis of the resulting broad peak ('boson peak') in terms of a correlation length. For the pseudo-binary (As2S3)x(P2S5)1-x glasses, Raman spectra are presented and analysed. In the frequency region up to the boson peak, the scattering intensity, corrected for thermal occupation, increases much more rapidly with increasing T above the experimental glass transition temperature T(g) than below T(g); I versus T is linear in both regimes (x = 0.5). A way of connecting this increase with the gradual glass <-> liquid transformation above T(g) is discussed.