Molybdenum ion as a structural probe in PbO-Sb

PbO-Sb2O3-B2O3 glasses containing different concentrations of MoO3 ranging from 0 to 5 mol % were prepared. A number of studies have been carried out on these glasses comprising differential thermal analysis, infrared and optical absorption, Raman and ESR spectra, magnetic susceptibility and measurements of dielectric properties (constant ε′, loss tan δ and a.c. conductivity $\sigma_{ac}$ over a range of frequency and temperature) of these glasses. The results have been analyzed in terms of different oxidation states of molybdenum ions. The analysis indicates that when the concentration of MoO3 is ≤0.6 mol %, molybdenum ions exist mostly in the Mo6+ state, occupy network forming positions with MoO$_{4}^{2-}$ structural units and increase the rigidity of the glass network. When MoO3 is present in higher concentrations, molybdenum ions seem to exist mostly in the Mo5+ state and occupy modifying positions