[SY-N6] Symposium N-6

[SY-N6] Simulating the collective diffusion mechanism of amorphous solids at experimentally relevant time scales

^○Yunjiang Wang^1,2, Shigenobu Ogata³ (1.Institute of Mechanics, Chinese Academy of Sciences, China, 2.School of Engineering Science, University of Chinese Academy of Sciences, China, 3.Graduate School of Engineering Science, Osaka University, Japan)

The nature of collective diffusion in amorphous solids is in strong contrast with diffusion in crystals. However, the atomic-scale mechanism and physics of collective motion remains elusive in disorder materials. Here the free energy landscape of collective diffusion triggered by single atom jump in a prototypical CuZr model metallic glass is explored with the recently advanced well-tempered metadynamics which significantly expands the observation time-scale of diffusion process at atomic-scale. Metadynamics samplings clarify a long-standing experimentally suggested collective diffusion mechanism in the deep glassy state. The collective nature is strongly temperature-dependent. It evolves from string-like motion with participation of only several atoms to be large size collective diffusion at high temperature, which would remarkably promote the atomic transport upon glass transition. The temperature and pressure dependence of collective diffusion are further quantified with big activation entropy and small activation volume of half atom volume, which both agree quantitatively with experiments. Direct atomic-scale simulations of diffusion at laboratory time-scale brings several physical insights into the nature of collective diffusion in amorphous solids which is beyond the knowledge established in diffusion of crystals.