Structure-Property Correlation in Sodium Borophosphate Glasses Modified with Niobium Oxide

Bulk glasses of the series (100-x)[0.4Na(2)O-0.2Nb(2)O(5)-0.4P(2)O(5)]-xB(2)O(3) with x = 0-48 mol% B2O3 were prepared by slow cooling in air. Their glass transition temperature increases within the range of 0-16 mol% B2O3, but further additions of B2O3 result in its decrease. Their structure was investigated by Raman, B-11, and P-31 MAS NMR spectroscopy. The relative number of BO4 units decreases with increasing B2O3 content, while the number of BO3 units increases up to 59 % at x = 48. The upfield shift of a broad resonance peak in the P-31 MAS NMR spectra is ascribed to an increasing connectedness of the structural network with increasing B2O3 content. Strong Raman band at 916-929 cm(-1) shows on the presence of NbO6 octahedra in the structural network of these glasses. With the B2O3 addition, a decrease in DC conductivity is observed, which is attributed to the decrease in the concentration of Na+ ions.