Mobility percolation as a source of Johari-Goldstein relaxation in glasses
Liang Gao, Yang Sun, Hai‐Bin Yu
Abstract
The Johari-Goldstein secondary (\ensuremath{\beta}) relaxations are intrinsic features of supercooled liquids and glasses, and they play a crucial role in several properties of glassy materials. However, their structural origin remains elusive. Prevailing theories consider them as localized activation or ``islands of mobility.'' In this study, we utilize atomistic simulations and percolation analysis to demonstrate that the mobile clusters are actually percolated at the occurrence of \ensuremath{\beta} relaxation, in seven different glassy systems. The percolation transition shows the same temperature and time dependence with \ensuremath{\beta} relaxation. Percolation emerges universally when about 10% of the atoms are mobile, and the dimension of the system-spanning cluster is approximately 2. Our findings add an essential piece to the full picture for the understanding of \ensuremath{\beta} relaxation in glasses.