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

Abstract

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 Sc 3+ exhibits the highest CFS but the lowest mass of all RE 3+ ions. We explore relationships between the glass composition and several physical properties, such as density, glass‐transition temperature ( T g ), Vickers hardness, and refractive index, over the glass forming region of the ternary Sc 2 O 3 – Al 2 O 3 – SiO 2 system. The glasses exhibit uniform and unexpectedly low T g ‐values (≈875°C), but a high microhardness (≈9.3 GPa) that correlates with the Sc 2 O 3 content. 29 Si 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. 27 Al MAS NMR reveals that besides the expected AlO 4 tetrahedra, substantial amounts of AlO 5 (31%–35%) and AlO 6 (≈5%) polyhedra are present in all Sc – Al – Si – O glass structures. 45 Sc isotropic chemical shifts (≈92 ppm) derived from MAS and 3 QMAS (triple‐quantum MAS ) NMR experiments are consistent with ScO 6 environments.