Raman scattering study of barium borate glasses and melts Original Research Article

Glasses and melts of x BaO–(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 (N 4) monotonously decreases with increasing BaO content in the melts structure, whereas N 4 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∅2−O⇔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.