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