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

The effect of WO 3 on the properties and structure of PbO–B 2 O 3 –P 2 O 5 –WO 3 quaternary system was studied. Glasses containing up to 60 mol% WO 3 were prepared and the variation of several physical properties was determined with respect to chemical composition in a broad compositional range. Chemical durability of WO 3 -containing glasses is very high and their thermal stability as well. Glass transition temperature increases with increasing WO 3 content up to 566 °C. Glass structure was studied by Raman spectroscopy and 31 P and 11 B MAS NMR spectroscopy. NMR spectroscopy reveals the formation of B–O–W linkages and also the existence of tetrahedral BO 4 units and trigonal units BO 3 in the glass structure. With increasing WO 3 content in the glasses, the number of starting tetrahedral B(OP) 3 O units decreases and B–O–P bridges are replaced gradually by B–O–W and B–O–B bridges, while the number of BO 3 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 W O bonds in tungstate structural units. In glasses with a higher WO 3 content WO 6 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. [ABSTRACT FROM AUTHOR]