The nature of structural relaxations during the glass formation process will be investigated using the viscous behavior of liquid oxide systems using the Brillouin light scattering technique. A signal in the GHz frequency range, related to a complex modulus, allows direct study of viscoelastic relaxation on an atomistic scale. Processes which reflect in the Brillouin spectrum include cooperative vibrations of larger molecular units, structural rearrangements involving bond breaking and reorientations and momentum exchange between diffusing particles. No mechanical coupling is necessary between the probe and the investigated substance, which eliminates some of the difficulties of high temperature measurements and facilitates the study of viscoelastic phenomena in the glass transition region. The fundamental relation between the experimental observations and the structural characteristics of glass.forming liquids is elucidated by complementary numerical simulations.
