The role of coordination and valance states of tungsten ions on some physical properties of Li2O-Al2O3-ZrO2-SiO2 glass system

A series of Li2O-Al2O3-ZrO2-SiO2 glasses doped with different concentrations of WO3 (0 to 5.0 mol.%) have been synthesized. Differential thermal analysis of the samples indicated increasing glass forming ability with the increasing concentration of WO3 in the glass matrix. A variety of spectroscopic (optical absorption, IR, Raman and ESR) and dielectric properties (over a range of frequency and temperature) of these glasses have been investigated. The optical absorption and ESR spectral studies have pointed out that a part of tungsten ions do exist in W5+ state in addition to WG+ state especially in the samples containing low concentration of WO3. The IR and Raman spectral studies have suggested that there is a decreasing degree of disorder in the glass network with increase in the concentration of WO3. The values of dielectric parameters viz., dielectric constant, loss and ac conductivity at any frequency and temperature are observed to decrease as the concentration of WO3 is increased. Such changes have been attributed to decrease of redox ratio or decreasing proportions of W5+ ions that act as modifiers in the glass network. The quantitative analysis of the results of ac conductivity and dielectric properties have indicated an increase in the insulating character of the glasses with the concentration of WO3; this is attributed to the presence of tungsten ions largely in W-6 (+) ions that participate in the glass network forming with WO4 structural units. (C) 2011 Elsevier B.V. All rights reserved.