Abstract
The series of Cr-Zn nano ferrites having the general composition CrxZnFe2-xO4 (0 ≤ x ≤ 0.5) have been synthesized successfully in the nanocrystalline form using the sol-gel method. The samples were sintered at 900°C for 3 hours. The effect of chromium substitution on dielectric properties of Zn-ferrites is reported in this paper. The analysis of XRD patterns revealed the formation of single phase cubic spinel structure for all the Cr-Zn ferrite samples. The FTIR spectra show two strong absorption bands in the range of 400 - 600 cm-1, which corroborate the spinel structure of the samples. The average grain size was found to be in the nanometer range and of the order of 43 - 63 nm obtained using TEM images. The lattice parameter and crystallite size decrease with increase in Cr concentration (x). The investigation on dielectric constant (e'), dissipation factor (D) and ac conductivity (σac) was carried out at a fixed frequency 1 kHz and in the frequency range of 100 Hz to 1 MHz at room temperature using LCR meter. The plots of dielectric constant (e') versus frequency show the normal dielectric behavior of spinel ferrites. The value of ac conductivity (σac) increases with increase in frequency for all the compositions. The appearance of the peak for each composition in the dissipation factor versus frequency curve suggests the presence of relaxing dipoles in the Cr-Zn nano ferrite samples. It is also found that the shifting of the relaxation peak towards lower frequency side with an increase in chromium content (x) is due to the strengthening of dipole-dipole interactions. The composition and frequency dependence of the dielectric constant, dielectric loss and ac-conductivity are explained based on the Koop’s two-layer model, Maxwell-Wagner polarization process, and Debye relaxation theory.
Highlights
Ferrites have paramount advantages over other types of magnetic materials due to high electrical resistivity and low eddy current losses [1] [2]
The current effort has been focused on studying the composition and frequency-dependent dielectric properties of Cr-Zn ferrites synthesized through sol-gel technique
As the frequency of the applied external field is increased beyond a certain value, the hopping frequency cannot follow up the field variation. It decreases the probability of the electrons reaching the grain boundary and as result polarization decreases which in turn causes to the decrement of dielectric constant
Summary
Ferrites have paramount advantages over other types of magnetic materials due to high electrical resistivity and low eddy current losses [1] [2]. Extrinsic losses are associated with the crystal defects, e.g. porosity, grain boundaries, micro-cracks, random crystal orientations, and impurities, etc It is evident from the previous studies [7] that the losses in sintered polycrystalline ceramics are greatly affected by these extrinsic factors. All these parameters can play a key role in the modification of the dielectric behavior of spinel ferrites which can be more useful for the desired applications. The current effort has been focused on studying the composition and frequency-dependent dielectric properties of Cr-Zn ferrites synthesized through sol-gel technique
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