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Title: Impedance Spectroscopy and DC Resistivity Studies on Substituted Cobalt ferrite (CFO) and Polymer-CFO Nanocomposites
Authors: Supriya, S.
Keywords: Physics
Issue Date: 2018
Publisher: IIT Patna
Series/Report no.: TH-90;
Abstract: Aiming to explore high dielectric material which is the prime requirement for the small size, lightweight, portable, electronic device in our today‟s life. Optimization is running to have devices with high battery backup along with minimal heat dissipation and fast charging rate. Therefore, the urge of dielectric material received attention in recent years for longevity and reliability of the devices. That requires a good dielectric material with understanding of their electrical transport property. Cobalt ferrite is one of the attractive material for basic research and technological application because of their unique magnetic and electrical properties. Cobalt ferrite has a special place owing to its unique magnetic properties. In addition to magnetic property, the study of electrical property of cobalt ferrite can provide critical information for many electronic applications. Electrical conductivity is basically due to the bound charge carrier and free charge carrier. The bound charge carrier has been studied in terms of impedance and ac conductivity and free charge carrier in terms of resistivity. The various equations and models like Debye equation, Arrhenius equation, Johnschers Power law, (Variable range hopping) VRH model, SPH (Small polaron hopping) model have been employed to understand the complete electrical transport properties of the material. Cobalt ferrite is a hard ferrimagnetic material which exhibits unique properties high Curie temperature, high coercivity, high magneto-crystalline anisotropy, moderate saturation magnetization, high dielectric permittivity, low eddy current losses, dielectric losses, good mechanical hardness, and chemical stability. These unique properties make it useful for development of microwave and spintronic devices, solar cells, magnetostrictive sensors, drug delivery, transducers, actuators, Li batteries, super capacitors, and memory devices, etc. Because of this unique feature, recently metal ion substitution for Fe3+/Co2+ ions in spinel ferrite gaining importance for utilization in high charge storage device as dielectric material in capacitors and battery applications. The specific nature of the metal ion substitution into a cobalt ferrite matrix can modulate the final electrical characteristics. The degree of modulation depends on the ionic radius, the electronic configuration of the substituting ion, and its site preference. The impetus of the present work is to derive a comprehensive study of the Cr3+, Mn3+, Al3+ respectively at Fe site of cobalt ferrite and Zn2+ at cobalt site and their impact on structural and electrical properties of nanocrystalline cobalt ferrite. The structural analysis has been carried out using XRD, FE-SEM, FTIR, RAMAN techniques. The electrical measurement carried out using impedance analyser as a function of frequency (1 Hz to 10 MHz) and temperature (313 K to 673 K). All samples found to be in spinel cubic structure with space group. The Cr3+ has larger ionic radius than Fe3+, Mn3+, Al3+ which infer greater perturbation than other substituents which has been also observed from the high value impedance obtained from Cr3+ substitution via impedance spectroscopy plots. Mn3+ has comparable size to that of Fe3+, which provides very little strain in the lattice site and no significant change was observed in impedance with Mn3+ substitution. The ionic radius of Al3+ is smaller than Fe3+ which gives an intermediate impedance value between Cr3+ and Mn3+ substituted cobalt ferrite. The Zn2+ substitution at cobalt site give high dielectric constant value for 10% substitution in cobalt ferrite as ionic radius of Zn2+ is larger than Co2+. The two transitions: dielectric transitions (TD)and magnetic transitions TM has been observed and correlated with the dc resistivity of cobalt ferrite, in which a broad hump has been observed for TD and a clear observation of ferrimagnetic transition has been observed in resistivity versus temperature plot which indicates that TD is due to bound charge carrier which has no clear appearance in the dc resistivity plot but TM is attributed to temperature dependant free charge carriers and clearly observed in impedance and dc resistivity plot. Among all four samples, Cr3+ substitution is the best substituent for the electrical transport properties as a high value dielectric material that is the order of 107 Ω.
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