Correlation between fragility and the Arrhenius crossover phenomenon in metallic, molecular, and network liquids

We report the observation of a distinct correlation between the kinetic fragility index m and the reduced Arrhenius crossover temperature θA=TA/Tg in various glass-forming liquids, identifying three distinguishable groups. In particular, for 11 glass-forming metallic liquids, we universally observe a crossover in the mean diffusion coefficient from high-temperature Arrhenius to low-temperature super-Arrhenius behavior at approximately θA≈2 which is in the stable liquid phases. In contrast, for fragile molecular liquids, this crossover occurs at much lower θA≈1.4 and usually in their supercooled states. The θA values for strong network liquids spans a wide range higher than 2. Intriguingly, the high-temperature activation barrier E∞ is universally found to be ∼11kBTg and uncorrelated with the fragility or the reduced crossover temperature θA for metallic and molecular liquids. These observations provide a way to estimate the low-temperature glassy characteristics (Tg and m) from the high-temperature liquid quantities (E∞ and θA).