Connecting the liquid fragility to the average weakest metal–oxygen bond of its crystal in oxides

Glass and crystal are inherently different material states in terms of their structural and physical features; consequently, the direct quantitative connection between crystal and glass is lacking. Herein, we first show that the liquid fragility m, which is featured by the negative departure degree of viscosity with the temperature at the glass transition temperature (Tg), has a direct exponential correlation with the ratio of the average longest metal-oxygen and the average phosphorus, silicon, or boron-oxygen bond lengths of the crystal in various oxides including phosphates, silicates, and borates. Such a result can be rationalized by the fact that the fragility m in these glass-formers is associated with the total network rigidity determined by the weakest bond due to the "bucket effect" and the bond pair inheritance of glass from that of the crystal. Our work connects direct features between glass and crystal with identical composition, providing a new viewpoint bridging glass and crystal.