LOW-FREQUENCY RAMAN-SCATTERING ON DIFFERENT TYPES OF GLASS FORMERS USED TO TEST PREDICTIONS OF MODE-COUPLING THEORY

We have measured low-frequency Raman scattering (RS) spectra of the glass formers B2O3, glycerol, m-tricresyl phosphate (m-TCP), and K3Ca2(NO3)7 in a broad temperature range above the glass transition temperature. The basic difference between the spectra is the ratio of relaxational to vibrational contributions: the more fragile the glass, the smaller is the vibrational contribution. Features of the relaxational contributions are quite similar. Testing predictions of mode-coupling theory (MCT) for m-TCP, we find that the dynamics is well described, and as the critical temperature we find T(c) approximately 260 K. In the case of glycerol, due to the strong vibrational contribution to the RS spectrum, a consistent interpolation of the rescaled data is only possible if other exponents than those predicted by MCT are applied; however, the MCT exponents are obtained in a narrow frequency range, provided the contribution of the alpha process is subtracted first. Thus, MCT describes the dynamics for nu < 300 GHz even in the nonfragile glass former glycerol. We extract T(c) approximately 3 10 K. Combining the RS results with those of NMR in the case of m-TCP, we further find (i) a change of stretching parameter close to T(c) and (ii) a change of the temperature dependence of the Debye-Waller factor at T approximately 280 K which is close to T(c) for this system.