Elsevier

Journal of Alloys and Compounds

Volume 726, 5 December 2017, Pages 187-194
Journal of Alloys and Compounds

Frequency and temperature dependence of conductance, impedance and electrical modulus studies of Ni0.6Cu0.4Fe2O4 spinel ferrite

https://doi.org/10.1016/j.jallcom.2017.07.298Get rights and content

Highlights

  • Electrical properties of Ni0.6Cu0.4Fe2O4 ferrite prepared by sol gel method have been studied.

  • The sample exhibits a semiconductor behavior in the temperature range of 300 K–500 K.

  • Z″ and M″ spectra show the existence of relaxation phenomenon in the present ferrite.

  • Relaxation process and electrical conductance are attributed to the same defect.

  • The relaxation process is due to the short-range mobility of charge carriers.

Abstract

Ferrite with nominal composition Ni0.6Cu0.4Fe2O4 was synthesized using Pechini sol-gel method. The X-ray diffraction results indicate that the ferrite sample has a cubic spinel type structure with Fd3¯m space group without any impurity phase. The electrical properties of this ferrite using complex impedance spectroscopy technique have been carried out as a function of frequency at different temperatures. The total conductance curves for the sample are found to obey Jonscher power law (G(ω) = GDC + n) with an increase of frequency exponent (n) as temperature increases. Frequency dependence of imaginary part of impedance (Z″) shows the existence of relaxation phenomenon in our sample. The impedance study using Nyquist representation revealed the appearance of semicircle arcs and an equivalent circuit of the type of (Rg + Rgb//ZCPE) has been proposed to explain the impedance results. Likewise, the analysis of the temperature variation of the imaginary part of modulus (M″) spectra confirms the existence of relaxation phenomena. Activation energies calculated from DC conductance, impedance and modulus spectra are in close agreement. This indicates that the relaxation process and electrical conductivity are attributed to the same defect.

Introduction

Spinel ferrites with general formula AB2O4 are a special class of magnetic materials. Due to their remarkable magnetic (e.g., high saturation magnetization, high Curie temperature TC), electric (e.g., semiconductor dielectric transition, massive magneto-resistance) and dielectric (e.g., high AC conductivity, high dielectric constant, low dielectric loss) properties have made ferrites more captivating to the nanoscience and nanotechnology fields [1], [2], [3], [4]. The electrical properties of these materials have been the subject of continuous investigation, which depend upon the preparation conditions, amount of doping element and doping level [5], [6]. It is well known that impedance spectroscopy is an important method to study the electrical properties of ferrites, since impedance of the grains can be separated from other impedance sources, such as impedance of electrodes and grain boundaries [7]. One of the important factors, which influence the impedance properties of ferrites, is the micro-structural effect. One semi-circle of Cole-Cole plots has been observed when the role of grain boundary is more dominant on the grain effect [8]. Likewise, the studies on the effect of temperature, composition and frequency on the dielectric behavior and AC electrical conductivity, providing valuable information about the conduction phenomenon in ferrites based on the localized electric charge carriers, which lead to better understanding of the electrical conduction mechanism and dielectric polarization in ferrites [9]. Along this line, spinel ferrites like Ni-Zn, Cu-Zn, Mn-Zn, Ni-Cu, Ni-Ca, etc. have been investigated in the recent years by many researchers in order to understand the nature of electrical conduction process in these materials [10], [11], [12]. N. Sivakumar et al. have studied the electrical properties of CoFe2O4 nanocrystalline through complex impedance spectroscopy, which show that the conductivity of the material increases with the decrease of grain size [13]. In Ref. [14], Rahman et al. have reported that the contribution of grain resistance in Mn-Ni-Zn ferrite is more than the grain boundary resistance. In their work, B. Ünal et al. have shown that ac conductivity (σac) of Co-doped Co-Zn ferrite varies with composition and temperature at low frequency regime [15]. Y. Köseoğlu has reported structural, magnetic, electrical and dielectric properties of Mn-doped NiFe2O4 ferrite nanoparticles synthesized by polyethylene glycol assisted hydrothermal process [16], [17]. For their part, E. Şentürk et al. have studied the temperature and frequency dependence of dielectric properties of Mn0.6Co0.4Fe2O4 nanoparticles synthesized by polyethylene glycol assisted hydrothermal method [18]. Furthermore, employing the same preparation technique, M. Tan et al. have reported structural, dielectric, temperature and frequency dependence of conductivity of Ni0.5Zn0.5Fe1.5Cr0.5O4 nanoparticles [19].

Along this line, the present work is devoted to investigate the electrical properties of Ni0.6Cu0.4Fe2O4 ferrite synthesized by Pechini sol-gel method using impedance spectroscopy technique in the frequency range of 40 Hz–107 Hz by varying temperature from room temperature to 420 K.

Section snippets

Experimental details

Spinel ferrite with composition Ni0.6Cu0.4Fe2O4 was synthesized by Pechini sol-gel method [20]. Stoichiometric amounts of nickel nitrate Ni(NO3)2.6H2O, copper nitrate Cu(NO3)2.3H2O and iron nitrate Fe(NO3)3.9H2O (all with purity better than 99%), were dissolved in distilled water. Subsequently, when these nitrates were completely dissolved in the solution, controlled amounts of citric acid (C6H8O7, 99% purity) were incorporated and dissolved with stirring. The molar ratio was fixed as 1:1 of

Microstructure and structural analysis

Fig. 1 shows the XRD pattern of Ni0.6Cu0.4Fe2O4 ferrite sample. There are almost no diffraction peaks corresponding to secondary phases, suggesting that pure phase was obtained. Using “X'Pert HighScore Plus” software, the diffraction peaks are indexed with respect to the cubic spinel type structure with the space group Fd3¯m. The diffraction peaks corresponding to the planes (111), (220), (311), (222), (400), (422), (511) and (440) provide a clear evidence for the formation of spinel structure

Conclusion

We have investigated the electrical properties of Ni0.6Cu0.4Fe2O4 ferrite using complex impedance spectroscopy technique. XRD pattern revealed that sample crystallizes in the cubic spinel structure with Fd3¯m space group. The electrical parameters DC/AC conductance, Z′, Z″, M′ and M″ have been studied as a function of both frequency and temperature. Electrical conductance curves show a semiconducting behavior of our sample. Nyquist plots of impedance show semicircle arcs for sample, and an

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