To Be or Not to Be Eutectic: Anomalous Glass Forming Ability Governed by Melt Structural Complexity

For decades, the search for metallic glass formers has followed a simple rule: go for the eutectics. However, this conventional wisdom has been challenged by a lingering mystery—certain congruent melting alloys exhibit higher glass‐forming ability (GFA) than their eutectic neighbors. Here, we unravel this anomaly by probing the structure of high‐temperature melt—the direct precursor to a glass. Using Ti‐Cu as a model system, we conduct a comparative study on a eutectic Ti 27 Cu 73 and its congruent melting counterpart Ti 50 Cu 50 . By combining aerodynamic levitation, in situ synchrotron x‑ray diffraction, and an energy minimization‐enhanced reverse Monte Carlo method, we resolve the atomic structures of these alloys in both the melt and glassy states. We reveal that the congruent melt is structurally more complex than the eutectic, exhibiting higher cluster diversity and stronger inter‑cluster correlations owing to the entropy‐enthalpy competition. This structural complexity is then inherited and amplified during the glass transition via cluster transformations, serving as dual kinetic and energetic barriers to crystallization that lead to the anomalously higher GFA. Our work establishes melt structural complexity as a new framework for understanding the glass transition at the atomic cluster level, with important implications for designing superior glasses from high‐entropy intermetallic alloys.