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

Abstract

Glasses in the BaO-MoO3–P2O5 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-xMoO3-(50-x/2)P2O5 (A), 50BaO-yMoO3-(50-y)P2O5 (B), 20BaO-zMoO3-(80-z)P2O5 (C) and (70-u)BaO-uMoO3-30P2O5 (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=40mol% MoO3 and in series C at z=50mol% MoO3, whereas monotonous increase of Tg in the series B and monotonous decrease in the series D was observed. 31P MAS NMR spectra of the glasses revealed depolymerization of the phosphate network, due to the incorporation of molybdate units, and isolated PO4 groups were identified in glasses with high MoO3 content. Fitting the NMR spectra provided compositional dependences of phosphate units Qn. On the Raman spectra of glasses with low MoO3 content, a strong vibrational band at 940–944cm−1, with a shoulder at ~910cm−1, dominated the spectra, which was assigned to the vibration of terminal oxygen atoms in molybdate structural units (MO– and MO). In glasses with high MoO3 content, a broad band at ~854cm−1, ascribed to MoOMo bonds, showed on the formation of octahedral clusters composed of MoO6 units in the structure of these glasses.