String-like atomic motions in metallic glasses as revealed by molecular dynamics simulations.

Dr. Haibin Yu has recently published his researh on the mechanism of secondary relaxation of metallic glass on Science Advances. The title of paper is “Structural Rearrangements Governing Johari - Goldstein Relaxations in Metallic Glass”. This work was collaborated with Prof. Ranko Richert in Arizona State University of U.S.A. and the University of Gottingen of Germany.

A lot of relaxation behaviors have been reported in amorphous solids (i.e., glassy state). Two fundamental relaxation modes, namely the alpha relaxation and beta relaxation, have been known in various kinds of amorphous substance, such as organic polymer/small molecule, oxide glass, amorphous drug, etc. Alpha relaxation (also known as primary relaxation) involved the diffusion movement of large range of particle in amorphous, whereas the beta relaxation (also known as the secondary relaxation) was related to the movements of local particles. In the glassy state materials, beta relaxation had close connection with glass transition, plastic deformation and other physical properties. Nevertheless, the physical mechanism of beta relaxation is still unclear.

In this study, Dr. Haibin Yu and collaborator applied a large-scale molecular dynamics simulation, which made simulation time scales (picosecond - microseconds) tended to be approach to experimental time scales (microseconds - seconds). They reported that the atomic motion mechanism of the beta relaxation in metallic glass: string-like motions (as shown) of the fast atoms in the seemingly random and chaotic system. The results also showed that there exist simple rule in the complexity and disorders.

The study not only clarified the atomic motion mechanism of the beta relaxation of amorphous materials, but also made it possible to control the properties of glasses by means of the beta relaxation of amorphous glassy state, and have implications for clarifying the nature of amorphous material in the future.

The research work was funded by the national natural science fund and the project of Thousand Youth Talents and received supports from Wuhan National High Magnetic Field Center. Some of the computational work was completed in National supercomputer center of Tianjin and Guangzhou.

The paper can be found:http://advances.sciencemag.org/content/3/11/e1701577