Light-scattering study of slow and fast dynamics in a strong inorganic glass former

The dynamic properties of glassy and liquid As2O3 are investigated over a w ide temperature range, in both the microscopic and macroscopic time domains by Brillouin scattering (BS) and photon correlation spectroscopy (PCS). Th e two characteristic properties of sound propagation, velocity, and attenua tion were found to exhibit considerable, although unexpected, changes very close to:the glass transition temperature T-g. The high-frequency density f luctuations were quantitatively treated using a phenomenological formulatio n for the corresponding memory function, which considers both slow-and fast processes. The obtained viscoelastic parameters were found to follow physi cally acceptable temperature dependencies. Both density and orientation aut ocorrelation functions show a very narrow distribution of relaxation times with a shape parameter close to 0.8, The peculiarities of the sound-velocit y and the sound-absorption coefficient as well as the comparison between th e PCS and the BS relaxation times confirmed the existence of two relaxation processes differing by 10 orders of magnitude near T-g, The difference in activation energies, for the fast process, between strong and fragile glass es is discussed on the basis of the stability of asymmetric double-well pot entials over a relaxation period. Evidence is provided conforming to the tw o fluid mode! predictions, invoking long-range density fluctuations. Pseudo transformations of chemically and topologically "acceptable" structures see m to be the driving force for low-energy excitations in network bonded glas ses. [S0163-1829(99)02446-7].