Raman scattering study of barium borate glasses and melts

Glasses and melts of xBaO–(100−x)B2O3 (x=20, 25, 30, 35, 40, 45, 50, 55, 60 and 67 mol%) composition have been prepared and studied using high-temperature Raman spectroscopy. It was shown that the structure of the glassy and molten samples with relatively low concentrations of barium oxide (x=20–35 mol%) consists of [B∅4]− charged tetrahedra (∅ is a bridging oxygen atom), B∅2O− asymmetric triangles (O− is a non-bridging oxygen atom) and B∅3 neutral units. The concentration of [B∅4]− tetrahedra (N4) monotonously decreases with increasing BaO content in the melts structure, whereas N4 demonstrates a maximum at x≈40 mol% in the glassy samples. B∅O22−B∅O22− pyroborate units appear at x≥40 mol%, and BO33−BO33− orthoborate anions are also formed in the melts structure when x=60 and 67 mol%. The dominant mechanisms for the structural reorganizations generated by changes in temperature depend on the melt composition. The changes in the short range order (SRO) structures can be described by the [B∅4]−⇔B∅2O− isomerization reaction at 2550 is most likely described by the 2B∅2O−⇔B∅O22−+B∅32B∅2O−⇔B∅O22−+B∅3 disproportionation reaction. In both cases, the equilibrium shifts to the right with an increase in temperature. Significant changes in the local structures of melts with a low concentration of barium oxide (x≤20 mol%) were not found.

► The structure of xBaO–(100−x)B2O3 (20≤x≤67 mol%) glasses and melts was studied by high-temperature Raman spectroscopy.
► The Raman spectra were analyzed in terms both of the SRO (short range order) and IRO (intermediate range order) structures.
► The temperature-induced changes in the melts mainly are due to the reorganization in IRO structures in B2O3-rich samples.
► The [B∅4]− tetrahedra monotonously decreased with increase in BaO content in the melts.
► The type of disproportional reaction depends on the melt composition.