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-yAl(2)O(3)(50-y)B2O3 (y = 2, 4, 6, 8 mol%), 50PbO-ySiO(2)-(50- y)B2O3 (y = 5, 10, 20, 30 mol%) and 50PbO-5SiO(2)-yAl(2)O(3)-(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 B-11 and Al-27 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-50B(2)O(3) glass. B-11 MAS NMR measurements determine that the fraction of tetrahedral borons (N-4) reaches a maximum for the glass containing 50 mol% of PbO in the PbO-B2O3 glass series and that N-4 is sharply reduced upon adding small amounts of Al2O3 into lead borate and lead borosilicate systems. Al-27 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. Al-[5] and Al-[6] 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. (C) 2009 Elsevier B.V. All rights reserved.