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

5 years ago

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

Mattias Edén, Thibault Charpentier, Baltzar Stevensson, Aleksander Jaworski

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 is decreased for ⁸⁹Y^[p] as well as ⁴⁵Sc^[p]. Second to the coordination number, we demonstrate that the ⁸⁹Y/⁴⁵Sc isotropic chemical shifts are mainly influenced by the RE/Al/Si constellation in the second coordination sphere of Y and Sc, where the shift tends to increase for emphasized contacts with neighboring RE and Al species at the expense of Si. These DFT-derived trends are corroborated by a progressive ⁸⁹Y deshielding observed in MAS ⁸⁹Y NMR spectra for increasing Y and/or Al content of the glass. We also introduce heteronuclear MAS NMR experimentation involving the pairs of ⁸⁹Y–²⁷Al and ⁴⁵Sc–²⁹Si nuclides, utilized for probing the contacts between the Y³⁺/Sc³⁺ cations and the AS glass-network forming groups.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b05471

DOI: 10.1021/acs.jpcc.7b05471