Structural study of WO3-La2O3-B2O3-Nb2O5 glasses

The effect of the addition of Nb2O5 to the WO3-La2O3-B2O3 glasses on their structure and physical properties (density, molar volume, glass transition temperature) has been investigated by using of IR and Raman spectroscopy, density measurement, and DTA analysis. Raman and IR spectra revealed that niobium ions incorporate into base tungstate glass matrix as NbO6 octahedra, interconnected by corners and edges. At lower Nb2O5 content (10 mol%), there is a high number of mixed B-O-Nb, and W-O-Nb bonds in the glass network. With increasing Nb2O5 concentration (15 mol% and 20 mo%), these bonds are gradually replaced by Nb-O-Nb linkages between corner shared NbO6 octahedra, forming 3D clusters, which are incorporated into amorphous network mainly trough La-O-Nb bonds. The addition of niobium oxide above 10 mol%, leads to decrease of the thermal stability of glasses and to increase in the density which is related with the formation of niobium oxide polyhedral clusters.