Structural and physical properties of MnO mixed lead zirconium silicate glass ceramics: Dielectric relaxation spectra and conduction phenomena

Abstract

In this study we have investigated the influence of MnO content on electrical characteristics (viz., dielectric properties including impedance spectra over wide ranges of continuous frequencies and temperatures, a.c and d.c. conductivities) of lead zirconium silicate glass ceramic with a view to assess its insulating character. Such assessment is crucial for using the material in different electronic devices, for example, as insulating sheets in the display panels. The variations of ε, tan δ (measured at different temperatures and frequencies) observed with the concentration of MnO are analysed in terms of structural transformations taking place in the glass ceramics. Although, the dielectric constant and loss tangent with temperature and frequency have not exhibited any distinct dipolar relaxation effects, the electric moduli (evaluated using real and imaginary parts of dielectric constant) have exhibits such effects clearly. Moreover, the variation of relaxation time (evaluated from electric moduli spectra) indicated multiple relaxation times for dipoles. Relaxation effects were ascribed to the complexes of octahedral Mn2+ ions. The conductivity (both ac and dc) with concentration of MnO exhibited the minima at 0.6 mol% of MnO. This effect is attributed to predominant presence of Mn ions in tetrahedral positions that were assumed to alternate with SiO4 units in the glass network. In the studied samples, both ionic and polaronic components are predicted to contribute to the conductivity. The polaronic component (arises due to exchange of polarons between Mn2+ ↔ Mn3+ ions) seemed to be gradually dominating over the ionic component with progressive insertion of MnO content up to 0.6 mol% in the bulk glass ceramic sample. The near temperature invariant part of σac behaviour (in the low temperature range) is analysed using both quantum mechanical tunnelling (QMT) model and the concentration of defect energy states near the Fermi level (N(EF), evaluated in this range of temperatures, was found to be the minimal for the sample M6. Analysis of dc conductivity results suggested the small polaron hoping (SPH) model holds good in the high temperature region; however, for the low temperature part of dc conductivity variable range hopping (VRH) model seems to be more appropriate. Finally, with the increase of MnO concentration up to 0.6 mol% in the titled glass ceramics, the conductivity decreases and leads to increase in the insulating strength of the material. This unique functionality may also make the investigated glass ceramic material perspective for medical applications in addition to their usage as insulating sheets in the display panels.