Dependence of glass forming ability on liquid fragility: Thermodynamics versus kinetics

The dependence of glass forming ability on liquid fragility is studied with thermodynamic and kinetic analyses. A general expression of the Gibbs free energy difference between an undercooled liquid and its equilibrium crystal is presented to address thermodynamically the fragility effect on glass formation. It is found that increasing fragility thermodynamically favors glass formation, remarkably contrasting with the fragility effect from the kinetic point of view. The dependences of glass forming ability on fragility in metallic alloys and molecular isomers are compared, and kinetics and thermodynamics of glass formation are, respectively, emphasized. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506900]