Abstract
If quenched fast enough, a liquid is able to avoid crystallization and will remain in a metastable supercooled state down to the glass transition, with an important increase in viscosity upon further cooling. There are important differences in the way liquids relax as they approach the glass transition, rapid or slow variation in dynamic quantities under moderate temperature changes, and a simple means to quantify such variations is provided by the concept of fragility. Here, we report molecular dynamics simulations of a typical network-forming glass, Ge–Se, and find that the relaxation behaviour of the supercooled liquid is strongly correlated to the variation of rigidity with temperature and the spatial distribution of the corresponding topological constraints, which ultimately connect to the fragility minima. This permits extending the fragility concept to aspects of topology/rigidity, and to the degree of homogeneity of the atomic-scale interactions for a variety of structural glasses.
Highlights
If quenched fast enough, a liquid is able to avoid crystallization and will remain in a metastable supercooled state down to the glass transition, with an important increase in viscosity upon further cooling
We show by using molecular dynamics (MD) simulations that a typical network-forming system with changing composition displays a certain number of relaxation dynamics anomalies that can be correlated with the strong or fragile nature of the corresponding supercooled liquids
Given that such isostatic compositions lead to a homogeneous distribution of mechanical constraints at the atomic scale, we argue that fragility deeply connects to the rigidity properties of the underlying network structure, and that fragile glasses are characterized by a spatial distribution of heterogeneous interactions
Summary
A liquid is able to avoid crystallization and will remain in a metastable supercooled state down to the glass transition, with an important increase in viscosity upon further cooling. We report molecular dynamics simulations of a typical networkforming glass, Ge–Se, and find that the relaxation behaviour of the supercooled liquid is strongly correlated to the variation of rigidity with temperature and the spatial distribution of the corresponding topological constraints, which connect to the fragility minima This permits extending the fragility concept to aspects of topology/rigidity, and to the degree of homogeneity of the atomic-scale interactions for a variety of structural glasses. It is detected that the compositions displaying an anomalous dynamics merely satisfy the well-known Maxwell stability (isostatic) criterion[10,11], while weakly depending on temperature Given that such isostatic compositions lead to a homogeneous distribution of mechanical constraints at the atomic scale, we argue that fragility deeply connects to the rigidity properties of the underlying network structure, and that fragile glasses are characterized by a spatial distribution of heterogeneous interactions. These conclusions are successfully compared with available experimental data that support the present findings, while emphasizing the general character of the results for a variety of structural glasses
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