Scandium and Yttrium Environments in Aluminosilicate Glasses Unveiled by 45Sc/89Y NMR Spectroscopy and DFT Calculations: What Structural Factors Dictate the Chemical Shifts?

Abstract

Aluminosilicate (AS) glasses incorporating rare-earth (RE) elements exhibit favorable mechanical and (magneto)optical properties that reflect their unusual structural organization. Yet, experimental reports on the local RE3+ environments in AS glasses are very sparse. We examine the Y3+ and Sc3+ cations in Y2O3–Al2O3–SiO2 and Sc2O3–Al2O3–SiO2 glasses of variable RE/Al/Si contents by utilizing magic-angle spinning (MAS) 89Y and 45Sc nuclear magnetic resonance (NMR) experiments coupled with density functional theory (DFT) calculations of 89Y/45Sc NMR chemical shifts. The DFT models reveal {Y[p]} and {Sc[p]} coordination numbers (p) spanning 5 ⩽ p ⩽ 8 and 4 ⩽ p ⩽ 7, respectively, with {Y[6], Y[7]} and {Sc[5], Sc[6]} species dominating. Wide isotropic chemical shift ranges of 35–354 ppm (89Y) and 48–208 ppm (45Sc) are observed, as well as sizable shift anisotropies up to ≈370 ppm and ≈250 ppm for 89Y and 45Sc, respectively. Both the isotropic and anisotropic chemical shifts grow when the coordination number p...