Direct observation of atomic network migration in glass

Many physical properties of glasses are still far from being understood at the atomic level. The lack of experimental methods capable of studying glassy dynamics at this scale has impeded the development of a complete model for atomic transport processes. Here we apply the new technique of atomic-scale x-ray photon correlation spectroscopy to directly observe single atomic motion in lead silicate glass. We show that dynamics change significantly depending on the glass composition, from single jump processes between inhomogeneous regions to multiple jump processes along network paths and through voids. Up until now, such measurements were far out of reach for temperatures below the glass transition. Our findings suggest that the method and the model introduced here will also help understanding atomic diffusion in a wide range of other glass systems. (paper)