Abstract: Despite its significance in both fundamental science and industrial applications, the glass-forming transition in the Al₂O₃-Y₂O₃ (AY) refractory system is not yet fully understood due to the elusive structure evolution upon cooling. Here, atomic-scale structural changes in AY-bearing melts with different compositions and temperatures are tracked by employing in situ high-energy synchrotron X-ray diffraction and empirical potential structure refinement simulation. We find that the glass-forming abilities (GFA) of AY-bearing melts are intriguingly correlated with the dependence of melt structure on temperature. In the case of the Al₂O₃ and Y₃Al₅O₁₂ (YAG), the observed large structural changes from superheating to undercooling melt (i.e., higher temperature susceptibility) correspond to a low GFA. Conversely, the 74Al₂O₃-26Y₂O₃ (AY26) melt, with the smallest temperature susceptibility, exhibits the highest GFA. Simulation models illustrate that the temperature susceptibility of melt is associated with its atomic arrangement, especially the stability of cation-cation pairs. A balanced network (in AY26 melt), where the unsteady OAl₃ tri-clusters are minimized and steady apex-to-apex connections between adjacent network units are abundant, contributes to stabilizing cationic interactions. This, in turn, fosters the formation of large-sized Al-O-Al rings, which topologically facilitates the subsequent glass-forming transition. Our findings provide new structural insight into the GFA of AY-bearing melts and may expand to other unconventional glass-forming systems to accelerate glassy materials design.

Key words: Glass-forming ability, Al₂O₃-Y₂O₃ glasses, Melt structure, High-energy synchrotron X-ray diffraction, Aerodynamic levitation, EPSR simulation