Molybdenum ion: a structural probe in lithium–antimony–germanate glass system by means of dielectric and spectroscopic studies

In this study, we have synthesized multi-component 10Li2O–(30 − x)Sb2O3–40GeO2–20PbO:x MoO3 (with five values of x ranging from 1.0 to 9.0) and investigated dielectric properties over a frequency range of 102–106 Hz and in the temperature range 30–300 °C of these samples. The evaluated dielectric parameters include dielectric constant, e′(ω); ac conductivity, σ ac; and electric modulus, M(ω). The results were interpreted with the aid of the experimental data on optical absorption, IR, Raman, and ESR spectroscopy. The analysis of the results of spectroscopic studies have indicated that a considerable proportion of molybdenum ions reduce to Mo5+ state, form molybdenyl complexes, occupy octahedral positions, act as modifiers, and create dangling bonds in the glass network. The concentration of such molybdenyl complexes seemed to be increasing with increase in the concentration of MoO3. The temperature dispersion of real part of dielectric constant, e′(ω), has been analyzed using space charge polarization model. The frequency and temperature dependence of the dielectric loss parameters have exhibited relaxation character. The relaxation effects have been attributed to molybdenyl complexes and to the divalent lead ions. Electrical conductivity exhibited an increasing trend and the activation energy showed a decreasing trend with increase in the concentration of MoO3. The increase of conductivity is attributed to (i) the increasing concentration of polaron Mo5+–Mo6+ pairs and (ii) increase in the concentration of dangling bonds in the glass network that causes the substantial decrement in jump distance for Li+ ions, which contribute to ionic conductivity.