Revealing the fast atomic motion of network glasses

• Published in: Nature communications 2014-05, Vol.5 (1), p.3939-3939, Article 3939
• Main Authors: Ruta, B., Baldi, G., Chushkin, Y., Rufflé, B., Cristofolini, L., Fontana, A., Zanatta, M., Nazzani, F.
• Format: Article
• Language: English
• Subjects: 639/301/1023/218; 639/766/36; Condensed Matter; Humanities and Social Sciences; Materials Science; multidisciplinary; Physics; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/ncomms4939

Still very little is known on the relaxation dynamics of glasses at the microscopic level due to the lack of experiments and theories. It is commonly believed that glasses are in a dynamical arrested state, with relaxation times too large to be observed on human time scales. Here we provide the experimental evidence that glasses display fast atomic rearrangements within a few minutes, even in the deep glassy state. Following the evolution of the structural relaxation in a sodium silicate glass, we find that this fast dynamics is accompanied by the absence of any detectable aging, suggesting a decoupling of the relaxation time and the viscosity in the glass. The relaxation time is strongly affected by the network structure with a marked increase at the mesoscopic scale associated with the ion-conducting pathways. Our results modify the conception of the glassy state and asks for a new microscopic theory. Studying relaxation in network-forming glasses on the atomic scale is experimentally challenging. Here, the authors perform X-ray photon correlation spectroscopy to study relaxation in sodium silicate at 297–762 K and show that fast atomic rearrangements occur even in the deep glassy state.