Structural investigation of BaOB2O3P2O5 glasses by NMR and Raman spectroscopy

• Changes in phosphate network were evaluated from 31P MAS NMR and Raman spectra.
• Fractions of BO4 and BO3 units were determined from 11B MAS NMR spectra.
• In the glasses with 0–20 mol% B2O3 only BO4 units exist in the glass structure.
• Fraction of BO3 units increases with B2O3 content but depends on the BaO content.
• Optimal network reticulation is achieved at glasses with 20–30 mol% B2O3.

Glasses of the ternary system BaOB2O3P2O5 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, 31P MAS NMR spectroscopy and 11B MAS NMR spectroscopy. The obtained results are discussed in several compositional lines A: (100-x)Ba(PO3)2xB2O3, B: 40BaOyB2O3(60-y)P2O5, C: (50-z)BaOzB2O350P2O5, D: (60-w)BaOwB2O340P2O5 and E: uBaO40B2O3(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 Tg is only steep within the region of 0–20 mol% B2O3 reaching a maximum at the glasses with ∼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 Q1 → Q2 → Q3 as detected from Raman spectra and 31P MAS NMR spectra. 11B 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)3O, B(OP)2O2 and BO3 in all the glasses of the glass forming region.

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