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 <or=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(P₂S ₅)_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 to or from liquid transformation above T_g is discussed.