Structural study of BaO-MoO3-P2O5 glasses by Raman and NMR spectroscopy

Glasses in the BaO-MoO ₃–P ₂O ₅ ternary system were prepared, their basic physical properties measured and their structure studied by Raman and ³¹P NMR spectroscopies. A modified glass-forming region in this system under slow cooling of the melt was determined. Four compositional series, namely (50-x/2)BaO-xMoO ₃-(50-x/2)P ₂O ₅ (A), 50BaO-yMoO ₃-(50-y)P ₂O ₅ (B), 20BaO-zMoO ₃-(80-z)P ₂O ₅ (C) and (70-u)BaO-uMoO ₃-30P ₂O ₅ (D) were chosen for a discussion on changes of the structure and properties of the studied glasses. The glass transition temperature revealed a maximum in series A at x = 40 mol% MoO ₃ and in series C at z = 50 mol% MoO ₃, whereas monotonous increase of T _g in the series B and monotonous decrease in the series D was observed. ³¹ P MAS NMR spectra of the glasses revealed depolymerization of the phosphate network, due to the incorporation of molybdate units, and isolated PO ₄ groups were identified in glasses with high MoO ₃ content. Fitting the NMR spectra provided compositional dependences of phosphate units Q ⁿ . On the Raman spectra of glasses with low MoO ₃ content, a strong vibrational band at 940–944 cm ^{− 1}, with a shoulder at ~ 910 cm ^{− 1} , dominated the spectra, which was assigned to the vibration of terminal oxygen atoms in molybdate structural units (M O ^– and M O). In glasses with high MoO ₃ content, a broad band at ~ 854 cm ^{− 1}, ascribed to Mo O Mo bonds, showed on the formation of octahedral clusters composed of MoO ₆ units in the structure of these glasses.