Influence of valence and coordination of manganese ions on spectral and dielectric features of Na2SO4–B2O3–P2O5 glasses

Sodiumsulpho borophosphate glasses with composition (40 − x)Na2SO4–30B2O3–30P2O5: xMnO with x ranging from 0 to 5.0 mol% were manufactures. Dielectric spectra have been studied over a wide frequency range of 102–105 Hz and in the temperature range within 30–250 °C. The valance states of manganese ions and their ligand coordination in the glass network have been investigated using optical absorption, luminescence and ESR spectroscopy. The analysis of the these results has indicated that the manganese ions exist both in Mn2+ as well as in Mn3+ states and occupy prevailingly octahedral positions and serve as modifiers similarly to Na+ ions The values of dielectric parameters (dielectric constant, ε′(ω), loss tan δ and ac conductivity, σac) were found to increase with increasing MnO content. They play a role of modifiers similarly to Na+ ions, create bonding defects and free ions viz., [SO4]2−, [POO1/2O2]2−, [POO0/2O3]3–, Na+ and (NaSO4)−. The migration of these charge carriers would build up space charge polarization and may be responsible for the enhanced dielectric parameters. The ac conductivity also is enhanced with increasing MnO content. The mechanism responsible for such increase is well explained based on the modifying action of Mn2+ ions.