Local structure, connectivity and physical properties of glasses in the B2O3-Bi2O3-La2O3-WO3 system

Abstract

Glasses of (100 - (x + y))·(0.6B2O3·0.4Bi2O3)·xLa2O3·yWO3, x = 0, 10; y = 0 ÷ 40 mol% were prepared by melt quenching. Density measurements, thermal analysis, UV–vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and theoretical modeling using Density Functional Theory were employed to identify the effect of WO3 content on the structural and physicochemical properties of these glasses. The glass transition temperature and density increase steadily with increasing WO3 content, most probably because of the formation of mixed Bi–O–W and La–O–W crosslinks. The lower band gap energy values show that the introduction of WO3 or La2O3 to 60B2O3·40Bi2O3 glass increases the number of non-bridging oxygen species in the glass structure. The photoelectron analysis aided by theoretical calculations discover that additionally to the tetrahedrally coordinated W ions, most of the existing WO6 octahedral units in glasses with nominal WO3 content below 20 mol% are distorted, leaving practically the tungsten ions in a quasi-tetrahedral coordination. At higher WO3 content (30–40 mol%) the concentration of octahedrally coordinated tungsten atoms dominate strongly over those of tetra- and quasi-tetra-coordinated W ions. Moreover, the comparison with appropriate crystal standards allows offering a complete description of the existing bridging and non-bridging linkages and their most likely O1s binding energies.