Understanding the Roles of V ₂ O ₅ and Nb ₂ O ₅ in the Network Structure of Alkaline Earth Aluminoborosilicate Glasses

ABSTRACT Owing to the possibility of attaining variable oxidation states and coordination numbers, the specific structural roles of V ₂ O ₅ or Nb ₂ O ₅ in determining the local configurations of framework species in alkaline earth aluminoborosilicate glasses still need to be disclosed. This manuscript describes the structural changes induced by adding 5 mol% of V ₂ O ₅ or Nb ₂ O ₅ to a complex aluminoborosilicate glass (mol%) 10MgO–15CaO–25SrO–5Al ₂ O ₃ –5B ₂ O ₃ –40SiO ₂ , aiming at elucidating the connectivity of these transition metal cations in the glass network. The resulting structural changes have been assessed by magic angle spinning‐nuclear magnetic resonance (MAS‐NMR) (for ²⁹ Si, ²⁷ Al, ¹¹ B, ⁵¹ V, and ⁹³ Nb nuclei), UV‐visible spectroscopy, scanning electron microscopy (SEM), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared and Raman spectroscopy, differential thermal analysis (DTA), molecular dynamics (MD) simulations, and density functional theory (DFT) calculations. XPS analysis indicated the presence of V and Nb with a 5+ oxidation state. The NMR spectroscopy, MD simulations, and DFT calculations suggest that V exists in 4‐, 5‐, and 6‐coordination, whereas Nb exists mostly in 6‐coordination. Both V and Nb are well incorporated into the silicate network. The results do not suggest any clustering of either of the V‐ or Nb‐based units.