Structure of lead borate glasses by Raman, 11B MAS, and 207Pb NMR spectroscopies

•Lead borate glasses with 30–80 mol% PbO were studied by Raman and NMR spectroscopy.•PbO changes its role from modifier to glass former at increasing lead oxide content.•The PbO bonding character changes from ionic to covalent at increasing PbO content.•The fraction of four-coordinated borons (N4) has a maximum near 50 mol% PbO.•Lead borate glasses are under-modified in comparison to alkali borate glasses. A multi-spectroscopic investigation of glasses xPbO-(100-x)B2O3, where 30 ≤ x ≤ 80, was undertaken employing Raman, 207Pb static NMR, and 11B MAS NMR spectroscopies. The Raman results were quantified and combined with quantitative NMR results to produce a coherent structural model. The fraction of four-coordinated borons (N4) has a maximum near x = 50, in contrast with alkali modified borates where the maximum is near x = 35–40. In the range x = 30–50, both NMR and Raman spectroscopies indicate that lead ion behaves more ionically. From x = 50–65, the spectroscopic results indicate a change in the lead-oxygen bonding character from ionic to covalent. At similar compositions, the borate network becomes more ionic while remaining under-modified compared to alkali borates; consistent with lead-oxygen bonding being important to the structural evolution. When x > 65, the lead-oxygen bonding becomes significantly covalent.