Composition-Property-Structure Correlations of Scandium Aluminosilicate Glasses Revealed by Multinuclear 45Sc, 27Al, and 29Si Solid-State NMR

Many features of aluminosilicate glasses incorporating a rare‐earth (RE) ion are dictated by its mass and cation field strength (CFS). Sc–Al–Si–O glasses are interesting because Sc3+ exhibits the highest CFS but the lowest mass of all RE3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass‐transition temperature (Tg), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc2O3–Al2O3–SiO2 system. The glasses exhibit uniform and unexpectedly low Tg‐values (≈875°C), but a high microhardness (≈9.3 GPa) that correlates with the Sc2O3 content. 29Si magic‐angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy shows enhanced deshielding and a minor glass‐network ordering as either the Al or Sc content of the glass increases. 27Al MAS NMR reveals that besides the expected AlO4 tetrahedra, substantial amounts of AlO5 (31%–35%) and AlO6 (≈5%) polyhedra are present in all Sc–Al–Si–O glass structures. 45Sc isotropic chemical shifts (≈92 ppm) derived from MAS and 3QMAS (triple‐quantum MAS) NMR experiments are consistent with ScO6 environments.