The influence of In2O3 on electrical characteristics of iron mixed Li2O–PbO–B2O3–SiO2–Bi2O3 multi-component glass system

Abstract

Glasses of the composition 19Li2O–20PbO–20B2O3–30SiO2–(10−x) Bi2O3–1Fe2O3: xIn2O3 with six values of x (0 to 5.0) were synthesized. Dielectric properties viz., dielectric constant, ε′(ω), loss, tanδ, ac conductivity, σac, electric modulus, M(ω) over wide ranges of frequency and temperature and also dielectric break down strength have been studied as a function of In2O3 concentration. The temperature dispersion of real part of dielectric constant, ε′(ω) has been analyzed using space charge polarization model. The dielectric loss (and also the electric moduli) variation with frequency and temperature exhibited relaxation effects and these effects were attributed to the divalent iron ion complexes. The ac conductivity exhibited maximal effect, whereas the activation energy for the conductivity demonstrated minimal magnitude at about 1.0mol% of In2O3. The conductivity mechanism is understood due to the polaronic transfer between Fe2+ and Fe3+ ions. The low temperature ac conductivity mechanism is explained following the quantum mechanical tunneling model. Spectroscopic studies viz., optical absorption and ESR spectra have revealed that the redox ratio (Fe2+/Fe3+) is maximal when the concentration of In2O3 is ~1.0mol%. The higher values of dielectric parameters observed at 1.0mol% of In2O3 are attributed to the presence of iron ions largely in divalent state and act as modifiers. The analysis of these results together with spectroscopic studies has indicated that when In2O3 is present in the glass matrix in higher concentrations (more than 1.0mol%) iron ions predominantly exist in trivalent state, occupy substitutional positions and make the glass more rigid. Such enhanced rigidity of the network is causing the decrease of dielectric parameters with the concentration of In2O3. Finally it is concluded that In2O3 mostly participate in the glass network in octahedral positions and make act as reducing agent (for iron ions) in the studied glass matrix when its concentration is ≤1.0mol%.