Strength of the repulsive part of the interatomic potential determines fragility in metallic liquids

The dynamical behaviour of liquids is frequently characterized by the fragility, which can be defined from the temperature dependence of the shear viscosity, eta (ref. 1). For a strong liquid, the activation energy for eta changes little with cooling towards the glass transition temperature, T-g. The change is much greater in fragile liquids, with the activation energy becoming very large near T-g. While fragility is widely recognized as an important concept-believed, for example, to play an important role in glass formation(2)-the microscopic origin of fragility is poorly understood. Here, we present new experimental evidence showing that fragility reflects the strength of the repulsive part of the interatomic potential, which can be determined from the steepness of the pair distribution function near the hard-sphere cutoff. On the basis of an analysis of scattering data from ten different metallic alloy liquids, we show that stronger liquids have steeper repulsive potentials.