By combining molecular dynamics (MD) simulations with 29 Si and 27 Al magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, we present a comprehensive structural report on rare-earth (RE) aluminosilicate (AS) glasses of the RE 2 O 3 −Al 2 O 3 −SiO 2 (RE = Y, Lu) systems, where the latter is studied for the first time. The structural variations stemming from changes in the glass composition within each RE systemas well as the effects of the increased cation field-strength (CFS) of Lu 3+ relative to Y 3+ are explored and correlated to measured physical properties, such as density, molar volume, glass transition temperature, and Vickers hardness (H V ). 29 Si NMR reveals a pronounced network ordering for an increase in either the RE or Al content of the glass. Al mainly assumes tetrahedral coordination, but significant AlO 5 and AlO 6 populations are present in all structures, with elevated amounts in the Lu-bearing glasses compared to their Y analogues. The MD-derived oxygen speciation comprises up to 3% of free O 2− ions, as well as non-negligible amounts (4−19%) of O [3] coordinations ("oxygen triclusters"). While the SiO 4 groups mainly accommodate the nonbridging oxygen ions, a significant fraction thereof is located at the AlO 4 tetrahedra, in contrast to the scenario of analogous alkali-and alkaline-earth metal-based AS glasses. The average coordination numbers (CNs) of Al and RE progressively increase for decreasing Si content of the glass, with the average CN of the RE 3+ ions depending linearly on both the amount of Si and the fraction of AlO 5 groups in the structure. The Vickers hardness correlates strongly with the average CN of Al, in turn dictated by the CFS and content of the RE 3+ ions. This is to our knowledge the first structural rationalization of the well-known compositional dependence of H V in RE bearing AS glasses.

systems. The density, molar volume, compactness, Vickers hardness, refractive index, as well as the glass transition (T g ) and crystallization temperature are compared for two series of RE-Al-Si-O (RE 5 La, Y, Lu, Sc) glasses that display a constant molar ratio n Al /n Si 5 1.00, whereas n RE /n Si is equal to either 0.62 or 0.94. Several glass properties scale roughly linearly with the cation field strength (CFS) of the rare-earth (RE 31 ) ion, except for the T g values of the Sc-bearing glasses that are significantly lower than expected. Magic-angle spinning 29 Si and 27 Al nuclear magnetic resonance (NMR) reveal enhanced network disorder and increased relative populations of AlO 5 and AlO 6 polyhedra in the aluminosilicate glasses for increasing RE 31 CFS, but overall similar Si and Al local environments (chemical shifts and quadrupolar couplings) in all samples associated with a constant n RE /n Si ratio, except for unexpectedly shielded 29 Si NMR signals observed from the Sc-Al-Si-O glasses.

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Many features of aluminosilicate glasses incorporating a rareearth (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. 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.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 3QMAS (triple-quantum MAS) NMR experiments are consistent with ScO 6 environments.