Glasses with xFe 2 O 3 -(20−x MnO 2 -80TeO 2 (x = 2, 5, 10, 15, and 20 mol%) composition were prepared by meltquenching technique to investigate the effects of mixed-transition metal ion Fe 2+/3+/ /Mn 3+/4+ on AC conductivity and dielectric properties using impedance spectroscopy. Dielectric constant showed strong variation with Fe 2 O 3 at a frequency ≥10 kHz, where decreased to a minimum value at x = 10 mol% before increasing for x > 10%. The decrease in 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 Fe 2 O 3 showed non-linear increase for x ≤ 10 mol% before dropping to a minimum at 15 mol% Fe 2 O 3 . 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 Fe 2 O 3 , 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.

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