Properties and structures of tin borophosphate glasses

The effects of B2O3-additions on the properties and structures of two series of Sn(II)-borophosphate glasses were determined. The addition of up to 28 mol% B2O3 to a 66.7SnO–33.3P2O5 base glass (series I), and the substitution of up to 13 mol% B2O3 for P2O5 in the same base glass (series II) increase Tg from 265 °C to 357 °C and 306 °C, respectively, while reducing the aqueous corrosion rates (at 40 °C) by an order of magnitude. The refractive index of the series I glasses decreases slightly, from 1.784 to 1.725, and increases for series II, to 1.834, at 632.8 nm. Raman spectroscopy reveals that borate additions to both series reduce the number of P–O–P linkages by converting pyrophosphate anions to orthophosphate anions. 11B NMR spectra indicate that tetrahedral borophosphate units, B(OP)4, are initially formed when B2O3 is added to the Sn-pyrophosphate base glass. More complex tetrahedral and trigonal borate sites form when B2O3 contents exceed about 10 mol%.