Structural features of MoO3 doped sodium sulpho borophosphate glasses by means of spectroscopic and dielectric dispersion studies

Na2SO4–B2O3–P2O5 glasses doped with different concentrations of MoO3 (ranging from 0 to 10.0 mol%) were prepared. The valence states of molybdenum ions and their coordination in the glass network have been investigated using optical absorption, ESR, and IR spectroscopy. The analysis of the spectroscopic results has indicated that the molybdenum ions exist in both Mo6+ (occupy octahedral and tetrahedral positions) and Mo5+ (occupy octahedral positions) local coordination sites and the redox ratio increases with the concentration of MoO3. Dielectric properties have been studied over a frequency range (102–105 Hz) and within the temperature range from 30 to 250 °C. The ac conductivity is observed to increase, whereas the activation energy for the conductivity exhibited decreasing trend, with the concentration of MoO3. In the low temperature region, the ac conductivity is nearly temperature independent and is varied linearly with frequency. Such behaviour is explained based on quantum mechanical tunneling (QMT) model. The dispersion of real part of dielectric constant ε′(ω), and loss, tan δ, with temperature have been analyzed on the basis of space charge and orientation polarization models.