Atomic origin and dynamics of structural relaxation in borosilicate glass below glass transition temperature

Abstract

Owing to their inherent non-crystalline nature, elucidating the structural relaxation of glass at the atomic scale presents significant challenges. In this investigation, 3 years of room temperature relaxation and in situ accelerated relaxation experiments were performed using a borosilicate glass. Additionally, the β relaxation activation energy of this borosilicate glass was determined by linear contraction monitoring, and the evolution of the network structure was characterized by a variety of spectroscopic techniques and simulated by molecular dynamics. The findings reveal that the atomic origin of the β relaxation below glass transition temperature can be ascribed primarily to the migration of the alkali ions. The network-forming units are disturbed by the alkali ions and make responses consequently. Specifically, [BO₃] triangles are inclined to accept a nonbridging oxygen from the [SiO₄] tetrahedra, transforming into [BO₄] tetrahedra with coordination changes, which ultimately leads to the formation of borosilicate rings. Such mechanism manifests the structural relaxation in borosilicate glass from the atomic scale and is expected to provide new insights into the microscopic nature of structural relaxation in oxide glasses.