Metallic Glass from the Point of View of Molecular Entropy Theory

Abstract The molecular entropy theory describes the glass transition as a cooperative molecular process. In theories’ equations, all thermodynamic and kinetic quantities of glass formation are expressed using molecular parameters. Two key molecular parameters are the size of the cooperative cluster and the average potential barriers per kinetic unit within the cluster. Equations has been established to measure the temperature dependence of both parameters The product of these two parameters defines the temperature dependence of the activation energy, which governs relaxation times, viscosity, and diffusion in glass formation. We found that, for all glass-forming substances, including metallic glass, the glass transition temperature is strictly proportional to the activation energy of the cooperative cluster at this temperature. Furthermore, we demonstrate that the size of the cooperative cluster at the glass transition temperature serves as molecular basis of the dynamic fragility (steepness) index.