Dielectric behavior and AC conductivity of Tb3+ doped Ni0.4Zn0.6Fe2O4 nanoparticles

Terbium doped Ni–Zn ferrite, Ni0.4Zn0.6TbxFe2−xO4 (x = 0, 0.05, 0.1, 0.15 and 0.2) have been prepared through sol–gel technique. Formation of single phase FCC spinel structure is identified in all the compositions using X-ray diffraction technique. The effect of Tb3+ doping on the crystalline phase, crystallite size, dielectric properties and AC conductivity has been investigated in detail. Lattice constant is observed to increase with terbium content; but beyond certain concentration of terbium (x > 0.15), it decreased. DC resistivity measurements were carried out in the temperature range 300–523 K. All the compositions exhibited usual semiconducting nature of ferrites and the resistivity of the samples found to increase with terbium content up to x = 0.15. The metallic behavior of the doped samples observed in the lower temperature region is explained in terms of elastic and inelastic scattering due to the rare earth ions. The investigations on dielectric constant, dielectric loss and AC conductivity was carried out in the frequency range 100 Hz–20 MHz from room temperature to 563 K. Frequency dependence of dielectric constant showed normal behavior and is in good agreement with Koop’s phenomenological theory of dielectric dispersion. AC conductivity measurements suggested conduction due to small polaron hopping. AC conductivity as well as dielectric constant is found to increase with temperature and which is due to thermally enhanced drift mobility of charge carriers. The observed decrease in dielectric loss with terbium content up to x = 0.15 is explained in terms of increase in resistivity.

► Tb3+ ions were successfully added into the lattice of Ni–Zn ferrite using sol–gel technique.
► Lattice parameter initially increases due to the expansion of unit cell and for x > 0.15, it decreases.
► Saturation magnetization decreases with Tb3+addition; however coercivity decreases up to x = 0.1 and then increases.
► Doped samples exhibited metallic behavior in the low temperature region and semiconducting nature there after.
► Maximum resistivity and least dielectric loss are achieved for the composition Ni0.4Zn0.6Tb0.15Fe1.85O4.