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

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.