Structural investigation of lithium bismuth borate glasses through Raman and infrared spectroscopies

The structure of lithium bismuth borate glasses in the compositional series xBi₂O₃–25Li₂O–(75 − x) B₂O₃ was studied with the use of Raman and infrared (IR) spectroscopies. Transparent glasses formed between x = 0 and 55, whereas glass–ceramics formed between x = 60 and 75 mol% Bi₂O₃. Structural investigation on the borate network showed that the glasses were undermodified at high Bi₂O₃ compositions with metaborate, pyroborate, and orthoborate triangles and tetrahedra being present past the stoichiometric orthoborate compositions (O/B = 3). Bi₂O₃ was found to participate in the glass as both a network former and modifier, as observed in the Raman and IR spectra. Optical absorption spectra of the glasses show a redshift of the absorption edge with increased Bi₂O₃. Optical, thermal, and physical properties of the glasses were examined and correlated to the structural evolution.