Binary Rare‐Earth Silicate Glasses Near Deep Eutectic: The Case for Sc ₂ O ₃ –SiO ₂ System

Homogeneous glass formation in binary rare‐earth silicate systems has thus far been precluded due to the presence of extensive liquid–liquid immiscibility and a strong tendency of these liquids toward crystallization. In this study, we demonstrate homogeneous glass formation in the Sc 2 O 3 –SiO 2 binary system within a narrow compositional window (37–39 mol% Sc 2 O 3 ) near a deep eutectic between the compounds Sc 2 Si 2 O 7 and Sc 2 SiO 5 , using containerless laser melting under aerodynamic levitation. The atomic structure of these unusual glasses is investigated using multinuclear ( 29 Si, 45 Sc, 17 O) solid‐state nuclear magnetic resonance (NMR) and Raman spectroscopy. The spectroscopic results, when taken together, provide a comprehensive picture of the structure of these glasses characterized by pyrosilicate [Si 2 O 7 ] 6− anionic units interconnected by Sc cations in ScO 6 coordination polyhedra, via Si–O–Sc linkages. A significant fraction (∼6%) of the oxygen atoms in the structure is present as free oxide (FO) ions in Sc–O–Sc linkages, providing connectivity between the ScO 6 polyhedra. The formation of the FO species via oxygen disproportionation reaction is promoted by the uniquely high field strength of the Sc 3+ ions, and the resulting structural frustration is hypothesized to suppress crystallization of the stable pyrosilicate phase in these liquids, enabling glass formation in an otherwise non‐glass‐forming binary system. These findings highlight the critical role of rare‐earth cation field strength in controlling oxygen speciation, structure, and glass‐forming ability in this binary silicate system.