Characterization and structural investigation of lead borophosphate glasses modified by tungsten oxide

Abstract

The effect of WO3 on the properties and structure of PbO–B2O3–P2O5–WO3 quaternary system was studied. Glasses containing up to 60 mol% WO3 were prepared and the variation of several physical properties was determined with respect to chemical composition in a broad compositional range. Chemical durability of WO3-containing glasses is very high and their thermal stability as well. Glass transition temperature increases with increasing WO3 content up to 566 °C. Glass structure was studied by Raman spectroscopy and 31P and 11B MAS NMR spectroscopy. NMR spectroscopy reveals the formation of B–O–W linkages and also the existence of tetrahedral BO4 units and trigonal units BO3 in the glass structure. With increasing WO3 content in the glasses, the number of starting tetrahedral B(OP)3O units decreases and B–O–P bridges are replaced gradually by B–O–W and B–O–B bridges, while the number of BO3 units increases. Raman spectra of the studied glasses possess a doublet of strong vibrational bands in the range at 800–1000 cm−1, assigned to vibrations of W–O− and WO bonds in tungstate structural units. In glasses with a higher WO3 content WO6 octahedra form tungstate clusters interconnected by W–O–W bridges as reflected in the Raman spectra. The formation of strong P–O–W and B–O–W linkages in the studied glasses explains high chemical durability of the glasses and the observed increase in the glass transition temperature.