Structure–property correlations in lead borate and borosilicate glasses doped with aluminum oxide

Glass samples from four systems: xPbO–(100−x)B2O3 (x = 30, 40, 50 and 60 mol%), 50PbO–yAl2O3–(50−y)B2O3 (y = 2, 4, 6, 8 mol%), 50PbO–ySiO2–(50−y)B2O3 (y = 5, 10, 20, 30 mol%) and 50PbO–5SiO2–yAl2O3–(45−y)B2O3 (y = 2, 4, 6, 8 mol%) were prepared by a melt-quench technique. Characterization of these systems was carried out using density measurements, UV–visible spectroscopy, differential scanning calorimetry (DSC), and 11B and 27Al magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR). Our studies reveal an increase in glass density with increasing lead(II) oxide concentration in pure lead borates and also with addition of silica into 50PbO–50B2O3 glass. 11B MAS NMR measurements determine that the fraction of tetrahedral borons (N4) reaches a maximum for the glass containing 50 mol% of PbO in the PbO–B2O3 glass series and that N4 is sharply reduced upon adding small amounts of Al2O3 into lead borate and lead borosilicate systems. 27Al MAS NMR experiments performed on glasses doped with aluminum oxide show that the Al3+ are tetra-, penta- and hexa-coordinated with oxygen, even without any excess concentration of Al3+ over charge-balancing Pb2+ cations. [5]Al and [6]Al concentrations are found to have unusually high values of up to 30%. The results of UV–visible absorption spectroscopy, DSC and density measurements support the conclusions drawn from the NMR studies, providing a consistent picture of structure–property relations in these glass systems.