Anomalous dielectric constant and AC conductivity in mixed transition-metal-ion xFe2O3-(20-x)MnO2-80TeO2 glass system

Glasses with xFe(2)O(3)-(20-x)MnO2-80TeO(2) (x=2, 5, 10, 15, and 20 mol%) composition were prepared by melt quenching technique to investigate the effects of mixed-transition metal ion Fe2+/3+//Mn3+/4+ on AC conductivity and dielectric properties using impedance spectroscopy. Dielectric constant showed strong variation with Fe2O3 at a frequency >= 10 kHz, where epsilon' decreased to a minimum value at x=10 mol% before increasing for x > 10%. The decrease in epsilon' may be attributed to some form of hindrance effect on heavy dipoles caused by the mixed transition-ion effect (MTE). Meanwhile, variation of AC conductivity with Fe2O3 showed non-linear increase for x <= 10 mol% before dropping to a minimum at 15 mol% Fe2O3. This result was attributed to Anderson localization because of the disorder in the glass system. Conductivity analysis showed that the conduction mechanism at the dispersion region for x = 2 mol% followed the correlated barrier hopping (CBH) model, while the mechanism transformed to the overlapping large polaron tunnelling (OLPT) model at higher Fe2O3, content (x > 2 mol%). The electric modulus of the investigated samples showed asymmetric peak of the imaginary part of electric modulus (M"), which reflected a non-Debye type relaxation.