Mobility percolation as a source of Johari-Goldstein relaxation in glasses

The Johari-Goldstein secondary (0) 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 0 relaxation, in seven different glassy systems. The percolation transition shows the same temperature and time dependence with 0 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 0 relaxation in glasses.

Automated summary

The Johari-Goldstein secondary (0) relaxations are intrinsic features of supercooled liquids and glasses, and play a crucial role in several properties of glassy materials. This study demonstrates through atomistic simulations and percolation analysis that the mobile clusters are percolated at the occurrence of 0 relaxation in seven different glassy systems. The percolation transition shows the same temperature and time dependence with 0 relaxation, and emerges universally when about 10% of the atoms are mobile, with a dimension of approximately 2 for the system-spanning cluster. These findings contribute to the understanding of 0 relaxation in glasses.