Structural heterogeneity has been identified as a critical factor in determining the mechanical and thermodynamic properties of glasses. However, its influence on glass formation has not been fully understood. Here we report the nanometer-scale chemical heterogeneity of Ag in a ribbon $\mathrm{C}{\mathrm{u}}_{45}\mathrm{Z}{\mathrm{r}}_{45}\mathrm{A}{\mathrm{g}}_{10}$ (at. %) metallic glass using Cs-corrected scanning transmission electron microscopy. Such heterogeneity is confirmed to occur in a $\mathrm{C}{\mathrm{u}}_{45}\mathrm{Z}{\mathrm{r}}_{45}\mathrm{A}{\mathrm{g}}_{10}$ model glass when the cooling rate is tuned below $\sim {10}^8$ K/s, as demonstrated by a hybrid Monte Carlo molecular dynamics simulation. A structural survey of ${\left(\mathrm{C}{\mathrm{u}}_{0.5}\mathrm{Z}{\mathrm{r}}_{0.5}\right)}_{100-x}\mathrm{A}{\mathrm{g}}_x$ (where $x$ ranges from 0 to 20) model glasses cooled at ${10}^6$ K/s reveals an inverse relationship between the fraction of icosahedral-like short-range order and the fractal dimensionality of chemical heterogeneity. Our findings demonstrate a significant role of fractal heterogeneity in promoting glass formation, a quantitative factor that has not been adequately addressed in prevailing theories of glass formation.

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• Glass transition
• Glasses
• Metallic glasses
• Electron microscopy