Structural investigation of BaO-B2O3-P2O5 glasses by NMR and Raman spectroscopy

Abstract

Glasses of the ternary system BaO-B2O3-P2O5 were prepared and studied in broad concentration limits covering the whole vitrification domain: 20-50 mol% BaO, 0-40 mol% B2O3 and 20-60 mol% P2O5. Their structure was studied with combinations of Raman spectroscopy, P-31 MAS NMR spectroscopy and B-11 MAS NMR spectroscopy. The obtained results are discussed in several compositional lines A: (100-x) Ba(PO3)(2)-xB(2)O(3), B: 40BaO-yB2O3-(60-y)P2O5, C: (50-z)BaO-zB2O3-50P(2)O(5), D: (60-w)BaO-w-B2O3-40P(2)O(5) and E: uBaO-40B2O3-(60-u)P2O5. Boron oxide incorporates into the phosphate network in the form of BO4 and BO3 groups and increases their glass transition temperature. Nevertheless, the increase in T-g is only steep within the region of 0-20 mol% B2O3 reaching a maximum at the glasses with similar to 30 mol% B2O3. In the lines A, B and E a decrease in the P2O5 and an increase of B2O3 content results in the shortening of phosphate chains with decreasing P2O5 content; these changes are most pronounced in line B with a constant BaO content. In lines C and D with a constant P2O5 content a decrease in the BaO content results, in contrast, in the reverse transformation of phosphate structural units in the direction Q(1) -> Q(2) -> Q(3) as detected from Raman spectra and P-31 MAS NMR spectra. B-11 MAS NMR spectra revealed that only BO4 units are present in the glasses with 0-20 mol% B2O3. In the glasses of the E series the fraction of BO3 units increases with a decreasing P2O5 content. By the decomposition of the 11B MAS NMR spectra it is possible to estimate the fractions of basic structural units formed by boron - B(OP)(3)O, B(OP)(2)O-2 and BO3 in all the glasses of the glass forming region.