A.C conductivity of cobalt substituted in copper ferrites by DSCM (original) (raw)
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Evaluation of AC conductivity & dielectric behavior of cobalt ferrite
Cobalt ferrite (CoFe 2 O 4) is a spinel ferrimagnetic oxide with high saturation magnetization, large magnetocrystalline anisotropy. Highly crystalline cobalt ferrite particles have been prepared using a new synthesis method i.e. microwave route. This microwave assisted route is one of the simplest and easy methods for synthesis. Here, cobalt ferrite (CoFe 2 O 4) is prepared by microwave route using thermal decomposition of cobalt oxalate precursor. Urea is used as a fuel for the solid-state combustion reaction. In this article, we report the investigation of ac conductivity and dielectric behavior of cobalt ferrite in the frequency range of 1 KHz to 1MHz and in the temperature range of 0 0 to 700 0 C. The obtained ac conductivity is found to be very low. The experimental results indicate an abnormal behavior in case of dielectric properties. Keywords: Cobalt ferrite, ac conductivity, microwave synthesis, dielectric behavior 1. Introduction: Cobalt ferrite is characterized by excell...
Correlation between AC and DC transport properties of Mn substituted cobalt ferrite
Journal of Applied Physics, 2016
The CoFe 2-x Mn x O 4 compound is prepared by following the sol gel technique. The structural analysis through XRD and Rietveld has been confirmed for the single cubic phase having Fd 3m space group for CoFe 2-x Mn x O 4 and also verified it through Raman spectroscopy measurements. The tetrahedral site observed to be red shifted with increase in Mn concentration in cobalt ferrite. All the XRD patterns have been analyzed by employing the Rietveld refinement technique. The particle size was found to be in the range of 30-40 nm. The electrical properties of polycrystalline CoFe 2-x Mn x O 4 for x ¼ 0.00, 0.10, 0.15, and 0.2, spinel ferrite was investigated by impedance spectroscopy. The influence of doping, frequency and temperature on the electrical transport properties of the CoFe 2-x Mn x O 4 for x ¼ 0.00, 0.10, 0.15, and 0.20 were investigated. The magnitude of Z 0 and Z 00 decreases with increase in temperature. Only one semicircle is observed in each Cole Cole plot which reveals that ac conductivity is dominated by grains. The grain resistance and grain boundary resistance both were found to decrease as a function of temperature. Temperature variation of DC electrical conductivity follows the Arrhenius relationship. A detailed analysis of electrical parameters provides assistance in connecting information regarding the conduction mechanism as well as determination of both dielectric and magnetic transition temperatures in the substituted cobalt ferrite. Detailed analysis of ac impedance and DC resistivity measurement reveals that, the magnetic ordering temperature in the Mn substituted cobalt ferrite does not respond to the frequency of ac electrical signal; however, it responds to the DC resistivity. The correlation between ac impedance and DC resistivity has been established.
AC conductivity of nanoparticles Co x Fe (1 À x) Fe 2 O 4 (x ¼ 0, 0.25 and 1) ferrites
Nanoparticles of Co x Fe (1 À x) Fe 2 O 4 (x ¼ 0, 0.25 and 1) were prepared by the chemical co-precipitation method. X-ray diffraction and scanning electron microscopy were used to determine the average particle size and morphology of the prepared samples. AC conductivity is found to vary as ω s in the frequency range 42–5 Â 10 6 Hz. The impedance analysis reveals that low conductivity and high impedance values are observed at low temperatures. The Nyquist impedance plots of the present investigation clearly depict the inherent phenomenon involved in the conduction mechanism of Co doped Fe 3 O 4 ferrites. Regarding frequency dependence of Co x Fe (1 À x) Fe 2 O 4 AC conductivity the observed behavior clearly indicates that the present ferrites are semiconductor-like.
Dielectric behaviour and a.c. conductivity in Cu x Fe 3− x O 4 ferrite
Bulletin of Materials Science, 2000
The dielectric properties (dielectric constant and loss) for the system Cu x Fe 3-x O 4 with x = 1⋅ ⋅0, 0⋅ ⋅8, 0⋅ ⋅6, 0⋅ ⋅4 and 0⋅ ⋅2, were studied in the temperature range 300 ∼ ∼ 800 K and also in the frequency range 1 kHz ∼ ∼ 1 MHz. A.c. conductivity was derived from dielectric constant and loss tangent data. The conduction in this system is interpreted as due to small polaron hopping. The dielectric relaxation was observed for the compositions with tetragonal structure whereas normal behaviour was observed for cubic structure.
arXiv: Materials Science, 2016
Chromium substituted cobalt ferrite with grain size less than the single domain (approx. 70 nm) has been prepared by the sol-gel method. XRD analysis reveals that the samples crystallize to cubic symmetry with spacegroup number 227. Two transition temperatures (TD (approx. 450 K) and TM (approx. 600 K) have been observed from the impedance verses temperature measurement. TD increases with the increase in frequency due to dipole response to the frequency. TM is comparable with the para-ferrimagnetic transition temperature of cobalt ferrite, which is independent of frequency. This result is well supported by the temperature dependent DC conductivity measurement. The modified Debye relaxation could be explained the impedance spectra of CoFe2-xCrxO4. The grain and grain boundary effect on impedance spectroscopy has been observed from Cole-Cole analysis. The ac conductivity follows Arrhenius behavior at different frequencies. All the samples exhibit the negative temperature coefficient o...
Materials Focus, 2017
The structural and dielectric properties were studied for Zn substituted copper spinel ferrite having the formula Cu 1-x Zn x Fe 2 O 4 where [x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0]. This ferrite prepared by an auto-combustion sol-gel method and calcined at different temperatures (500, 800, and 1100 o C). The X-ray diffraction pattern of these compositions showed the formation of the single phase spinel structure. Furthermore, the XRD have been used to calculate the lattice parameter, particle size, bulk density and porosity for all ferrite samples. The particle size varied from 18.5 nm to 36 nm, while the lattice parameter decreased with calcination temperatures and Zn-ion content in the range (8.2688-8.3304 A o). X-ray density decreases from 5.536 to 5.562 g/cm 3 and porosity increases from 6.4 to 12.8 % with increasing Zn-ion content. The dielectric constant decreases from 56*10 3 to 26*10 3 and the loss tangent from 8.52 to 0.33 with frequency (in the range of 50 Hz-5MHz), while the dielectric constant takes high values with high Copper content ferrites. a.c. Conductivity increases (from 0.27*10-5 to 168 *10-5 Ω-1 .cm-1) with increasing frequency. On other hand; A.C. Resistivity decreases (from 361*10 3 to 0.59*10 3 Ω.cm) with frequency for all Cu-Zn ferrite samples.
JMMM, 2018
In this study, we report frequency and temperature dependent dielectric, electrochemical impedance and low temperature magnetic properties of Sol-gel auto-combustion synthesized rare-earth (Ce and Sm) co-substituted cobalt ferrite, CoCe x Sm y Fe 2-x-y O 4 (x = y = 0.00, 0.1, 0.12 and 0.25). The surface morphology and particle size as obtained by XRD studies was confirmed by HRTEM measurements for a representative sample. The dielectric properties such as dielectric constant, loss tangent and AC conductivity have been measured using LCR meter, variation of dielectric parameters with substituent concentrations, frequency range from 0.1 to 10 MHz at room temperature (RT) and temperatures 100-400 °C have been well supported by Maxwell-Wagner interfacial polarization. The AC conductivity increased with applied frequency suggesting that the conduction mechanism is owing to small polaron hopping between cations. Impedance studies shows that, the addition of RE (Ce and Sm) cause a decrease in the Z′ value, with increasing frequency which can be attributed to the space charge polarization effect in the material. Low temperature magnetic measurements in ZFC-FC mode and magnetic isotherms at 20 and 310 K reveals the ferromagnetic nature of RE (Ce, Sm) substituted cobalt ferrite nano particles. The coercive field has been increased at low temperature 20 K compared to that at 310 K, the samples shows super paramagnetism beyond room temperature.
Electrical conductivity and microcrystalline parameter in Co–Zn ferrites
Materials Research Innovations, 2011
A series of samples of the system Co 12x Zn x Fe 2 O 4 (for x50?0, 0?2, 0?4, 0?6 and 1?0) were prepared by usual ceramic technique. These prepared samples were examined using X-ray powder pattern, which confirms the presence of a spinel structure. The authors have also carried out line profile analysis of individual Bragg reflections observed in these ferrites, which shows variation in the cell parameter. Further electrical conductivity measurements of these ferrites were carried out as a function of temperature. The observed values of the electrical conductivity have been explained on the basis of Verwey's hopping mechanism. The activation energy was found to decrease with increasing Zn content. In addition, its variations for varying concentrations of Zn in Co are interpreted in terms of microstructural parameters.
Dielectric and transport properties of Zn-substituted cobalt ferrites
Journal of Bangladesh Academy of Sciences, 2013
Effect of Zn content on the dielectric and transport properties of CoZn x Fe 2-x O 4 (x = 0.0, 0.1, 0.2, 0.3 and 0.4), prepared by standard double sintering ceramic technique, sintered at 1000 o C for 4 hours were investigated. The X-ray diffraction (XRD) pattern of the prepared samples showed single phase inverse-spinel structure without any detectable impurity. Lattice constant of the samples increased with the increasing Zn concentration which follows Vegard's law. The theoretical densities of these samples remained almost constant whereas the bulk density decreased with Zn content up to x = 0.2. But with further increase of Zn content the bulk density increased. The porosity of the prepared samples showed the opposite trend. The dielectric constant (є′) measurement showed the normal dielectric behavior of the prepared ferrite. The DC electrical resistivity of the prepared samples decrease with increasing temperature which indicates the semiconducting behavior of the prepared ferrites. The Zn concentration showed pronounced effect on the resistivity at room temperature. Possible explanation for the observed features of densities, porosity, dielectric constant and resistivity of the studied samples are discussed.