Structural study of PbO–MoO3–P2O5 glasses by Raman and NMR spectroscopy

Glasses in the ternary system PbO–MoO3–P2O5 were prepared in three compositional series (100 − x)[0.5PbO–0.5P2O5]–xMoO3 (A), 50PbO–yMoO3–(50 − y)P2O5 (B) and (50 − z)PbO–xMoO3–50P2O5 (C) and their structure was studied by Raman and 31P NMR spectroscopies. In the compositional series (100 − x)[0.5PbO–0.5P2O5]–xMoO3 homogeneous glasses were prepared in the concentration region of 0–70 mol% MoO3. Their glass transition temperature increases with increasing MoO3 content having a maximum at x = 50 mol% MoO3. 31P MAS NMR spectra reveal that in the glass series (A) the incorporation of MoO3 results in the shortening of phosphate chains and gradual transformation Q2 units into Q2 and Q0 units, prevailing in glasses with a high MoO3 content. Octahedral structural units MoO6 dominate in most glass compositions and they are present also in the structure of Pb(MoO2)2(PO4)2 compound corresponding to the glass composition 50Pb(PO3)2–50MoO3. The analysis of Raman spectra of glasses of the (B) series with a high MoO3 content showed the transformation of octahedral MoO6 units into tetrahedral MoO4 units.