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 theta(A) = T-A/T-g 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 theta(A) approximate to 2 which is in the stable liquid phases. In contrast, for fragile molecular liquids, this crossover occurs at much lower theta(A) approximate to 1.4 and usually in their supercooled states. The theta(A) values for strong network liquids spans a wide range higher than 2. Intriguingly, the high-temperature activation barrier E-infinity is universally found to be similar to 11k(B)T(g) and uncorrelated with the fragility or the reduced crossover temperature theta(A) for metallic and molecular liquids. These observations provide a way to estimate the low-temperature glassy characteristics (T-g and m) from the high-temperature liquid quantities (E-infinity and theta(A)).