Correlation between Fragility and the Arrhenius Crossover Phenomenon in Metallic, Molecular, and Network Liquids

TL;DR

This study uncovers a universal correlation between fragility and the Arrhenius crossover in various glass-forming liquids, revealing distinct behaviors in metallic, molecular, and network liquids and enabling predictions of glassy properties from high-temperature data.

Contribution

It identifies a universal relationship between fragility index and crossover temperature across different liquids, providing a new way to estimate glassy properties from high-temperature measurements.

Findings

Metallic liquids show crossover at $ heta_A \\approx 2$ in stable phases.

Molecular liquids exhibit crossover at lower $ heta_A \\approx 1.4$ in supercooled states.

Activation barrier $E_\\infty$ is universally about 11 $k_B T_g$ and uncorrelated with fragility.

Abstract

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 $\theta_A \approx 2$ which is in the stable liquid phases. In contrast, for fragile molecular liquids, this crossover occurs at much lower $\theta_A \approx 1.4$ 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 $E_\infty$ is universally found to be $\sim 11\ k_B T_g$ 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 ($E_\infty$ and $\theta_A$).