Stretched and compressed exponentials in the relaxation dynamics of a metallic glass-forming melt

• Published in: Nature communications Vol. 9; no. 1; pp. 5334 - 7
• Main Authors: Wu, Zhen Wei, Kob, Walter, Wang, Wei-Hua, Xu, Limei
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.12.2018; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 639/766/119/1002; 639/766/530/2804; Amorphous materials; Computer simulation; Condensed Matter; Disordered Systems and Neural Networks; Dynamics; Glass; Glass formation; Humanities and Social Sciences; Icosahedrons; Mathematical models; Metallic glasses; multidisciplinary; Physics; Relaxation time; Scattering functions; Science; Science (multidisciplinary); Statistical Mechanics; Temperature dependence; Time dependence; Transition temperatures
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-018-07759-w

The dynamics of glass-forming systems shows a multitude of features that are absent in normal liquids, such as non-exponential relaxation and a strong temperature-dependence of the relaxation time. Connecting these dynamic properties to the microscopic structure of the system is challenging because of the presence of the structural disorder. Here we use computer simulations of a metallic glass-former to establish such a connection. By probing the temperature and wave-vector dependence of the intermediate scattering function we find that the relaxation dynamics of the glassy melt is directly related to the local arrangement of icosahedral structures: Isolated icosahedra give rise to a liquid-like stretched exponential relaxation whereas clusters of icosahedra lead to a compressed exponential relaxation that is reminiscent to the one found in a solid. Our results show that in metallic glass-formers these two types of relaxation processes can coexist and give rise to a dynamics that is surprisingly complex. Glasses show peculiar relaxation dynamics below glass transition temperature, yet a deeper understanding of this phenomenon is still lacking. Wu et al. show the coexistence of stretched and compressed relaxation in a metallic glass system and attribute their origins to different local cluster structures.