Sreenu Kasam 1* Bhargavi T 2. Department of Physics, Wollega University, Nekemte 395, Ethiopia 2

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1 Page No.4 eissn x International Association of Advances in Research and Development International Journal of Basic And Applied Sciences International Journal of Basic and Applied Sciences, 2015, 1(1),4-8 Research Article Structural and AC conductivity studies of Ni-Zn ferrite prepared through coprecipitation method Sreenu Kasam 1* Bhargavi T 2 1 Department of Physics, Wollega University, Nekemte 395, Ethiopia 2 Sri Indu College of Engineering and Technology Ranga Reddy Telangana, India *corresponding author: cnukasam@gmail.com Abstract: The Nickel-Zinc Ferrite (NZF) is a well-known mixed inverse spinel ferrite. Nickel-zinc ferrites is a class of technologically important soft ferrite better known for its microwave absorbing property in addition to many side functioning and applications. Microwave absorption properties are highly dependent on processing parameters and chemical composition. However, the crystal size, magnetic properties, complex magnetic permeability and complex permittivity can greatly influence DC resistivity, AC conductivity, dielectric property, and hence the electrical property of the materials, the conduction mechanism of ferrites is explained on the basis of hopping of charge carriers between Fe +2 and Fe 3+ at the octahedral sites. In the present paper reporting lattice parameters, the structure, crystalline size and AC conductivity mechanism with frequency for of the NiX-Zn1-X Fe2O4 for x= 0.5 and 0.65 co-precipitation synthesized samples Keywords: Ferrite, Microwave, co-precipitation, AC conductivity, conduction mechanism, Introduction The activity in ferrites began with the search for ferromagnetic properties and having low eddy current losses [1]. Since the eddy current losses in ferromagnetic materials are inversely proportional to the resistivity, they can be minimized by the use of magnetic materials of high resistivity. The foundation of modern interest in ferrites was laid by Snoek [2] in 1945.The experimental work of Snoek and the basic theory of ferromagnetism developed by Neel [3], were the starting points for the rapid expansion of research activity in ferrite industry. The Nickel-Zinc Ferrite (NiXZn1-XFe2O4 or NZF) is a well-known mixed inverse spinel and soft ferrite. The unit cell of the inverse spinel ferrites comprises of 32 oxygen atoms located in a cubic closed packed structure, distributed in the tetrahedral (A) sites and octahedral (B) sites. The relative permeability for these ferrites at room temperature can range from about 15 to It s Saturation Magnetization and at Curie temperatures range from 2 to 3.5 kilogauss and 125 to 500 o C respectively. Also its resistivity is in the order of Ωm. Spinel ferrites with different nickel (Ni) and zinc (Zn) composition are of great interest due to their potential application in microelectronics, magneto optics and as microwave devices component. NZF nanocrystals possess good dielectric and magnetic properties. These properties are influenced by different factor like the choice of the cations, the manner in which they are spread among the tetrahedral and octahedral sites, the sintering temperature, doping additives, preparation conditions, chemical composition and the method of preparation. There are several physical and chemical methods available such as combustion technique, co-precipitation, sol-gel, spray paralysis, high energy ball milling for fabricating chemically and stoichiometric pure NZF nanocrystal [4]. Permeability of NZF is high at about 30% mol NiFe2O4 and 60% mol ZnFe2O4. Resistivity is as high as10 2 to10 7 Ωm. The high frequencies characterization depends on the concentration of Zinc [5]. The frequency dependences of AC electric conductivity of Ni-Zn ferrite were studied [6]. It is observed that the AC electrical conductivity increases with increasing applied frequency. Since the increase in frequency enhances the hopping frequency of the charge carriers Fe +2 and Fe +3 the conduction is observed to increase. The conduction mechanism of ferrites is explained on the basis of hopping of charge carriers between Fe +2 and Fe 3+ at the octahedral sites. Nickel-zinc ferrites is a well-known class of technologically important soft ferrite better known for its microwave absorbing property in addition to many side functioning and applications. Microwave absorption properties are highly dependent on processing parameters and chemical composition. However, the crystal size, magnetic properties,

2 Page No.5 complex magnetic permeability (εr) and complex permittivity (µr) can greatly influence DC resistivity, AC conductivity, dielectric property, and hence the electrical property of the materials [7]. The NZF is a well-known mixed inverse spinel, whose unit cell is represented by the formula [Ni1 xfe1+x][znxfe1 x]o4. The concentration of Ni and Zn ions in NZF induces changes in the defect structure and texture of the crystal, creating significant modifications in the magnetic and electrical properties. However, the synthesis route also plays a crucial role, so that samples of comparable crystallite size prepared by different processes show different structural, magnetic and electrical properties. There are many methods to synthesize NZF, such as co-precipitation, thermal plasma, hydrolysis [8]. Among the existing synthesis techniques; the co-precipitation method has drawn much attraction owing to its inherent advantages such as homogeneity in the reactant distribution, low processing temperature, simple and economically viable to synthesize of nanocrystal. The end products of the method exhibit a very narrow size distribution and also have a uniform shape. The concentration of Zn and Ni influences on the structure and its properties of NZF can be studied. When the concentration of Zn increases in NZF the lattices constant and volume of crystal are increase, where as it slightly decreases in crystal size, calculated density and average inter planar space between planes ferrites are made by the reaction sol-gel method [9]. This thesis work focus on the synthesis and characterization of NiXZn1-XFe2O4 nanocrystal for different value X, where X is 0.5 X 0.65 on the interval of 0.15 prepared by Coprecipitation method. 2. Materials and Methods Synthesis of Ni x -Zn 1-x Fe 2 O 4 (Ni-Zn Ferrite or NZF) nanocrystal powder by co-precipitation method for different value of X (for X =0.5 and X=0.65). Chemical reaction, process by which atoms or groups of atoms are redistributed, results in a change in the molecular composition of substances and its property. The properties of ferrite nanocrystal is strongly influenced by preparation methodology, chemical composition, purity and exact amount of the reactant; therefore the synthesis of ferrite nanocrystal needs special processing techniques, appropriate chemical composition and exact amount of reactant to achieve high quality of end product with repeatable properties. The co-precipitation technique is the process in which the reactant species (metallic salts, nitrate, carbonate, oxalate, sulfate.) [10-11] are dissolved in distilled water or some aqueous/organic medium in an appropriate proportion and with the addition of an inorganic solvent (sodium hydroxide, ammonia, or hexane), ph of the solution is adjusted in between 8 to 12 under continuous stirring. Sometimes, heat is also provided to complete the reaction. Precipitates are settled at the bottom of cylindrical beaker. They are filtered and washed with distilled water several times to remove impurities and are dried in air. In order to develop the final structure, powder is calcined in oven. The step for the synthesis of Ni-Zn Ferrite with different concentrations is the powder synthesized using the Ni precursors, as Nickel nitrate (Ni(NO3)2.6H2O), Zn precursors, as Zinc nitrate Zn(NO3)2.6H2O and Fe precursors, as FeCl3 with the reaction: XNi (NO3)2 6H2O + (1-X) Zn (NO3)2.6H2O +FeO > NixZn1-xFe2O4 + 2NO2 + ½ 02 The aqueous solution of the Ni-Zn ferrite was used as the alkaline mineralize. The ph of the solution was maintained using the aqueous solution of NaOH. The temperature of the reaction increases from room temperature to elevated temperature. The experimental techniques used for characterization are X-ray diffraction (XRD) PHILIPS Pan analytical x-ray difractometer, scanning electron microscopy (SEM) is model N360 HITACHI Japan and conductivity is AUTOLAB PGSTAT 30, were conducted to identify its structure, grain size and morphology and AC electrical conductivity of NZF nanocrystals. 3. Results and Discussions 3.1. XRD Analysis The fine sintered powder Ni-Zn ferrite is charectarized by XRD that X-ray diffraction with the 2θ range from 20 0 to 80 0 at room temperature using CuKα radiation. The XRD patterns are obtained at the scanning rate of 2 0 /min (2θ). The d- spacing (inter -planar space between plane) and crystalline size is determined using Bragg's and Scherer equation respectively. Fig.1 shows the XRD pattern of NiX-Zn1-X Fe2O4 for x=.05 and x=0.65 respectively. The sharp peaks indicate the high crystalline of the ferrite particles. The XRD profile in both ferrite samples is in agreement with the JCPDS data card number , which indicate the single phase formation of cubic spinel. (400) and (422) peaks around 2θ= , for x=0.65 and 2θ = for x=0.5 are observed The average crystallite size of the nanocrystal in each case was calculated from (311) peak of corresponding XRD peaks by using Scherer s equation and found to be near for (a) 22.5nm and for (b) 24.5nm for X=0.5 and X=0.65,

3 Page No.6 respectively. The average crystallite size of ferrite samples decreases when we increase the concentration of Nickel. This is in agreement to the reported literature [12] (311) x = (311) x = 0.65 Intensity (arb. units) (111) (220) (222) (400) (422) (511) (440) (533) Intensity (arb. units) (111) (220) (222) (400) (422) (511) (440) (533) 0 2θ 2θ Fig 1 XRD patterns of Ni0.5Zn0.5Fe2O4 and Ni0.65Zn0.35Fe2O4 Different parameters like crystallite size, the increase in the concentration of Nickel. The bulk density, X-ray density, lattice parameter, interplanar space between plane and porosity are can be attributed to the larger ionic radius of Zn 2+ linearly increase of lattice constant with Zn content calculated for each ferrite sample and presented in (0.84A o ) as compared to ionic radius of Table 1. lattice parameter were calculated using Ni 2+ (0.74A 0 ) [15]. The determined lattice parameters Powd software Å for ferrite samples at confirm that the nano-crystalline ferrite samples are X=0.65 it is to be Å for sample X=0.5 these in cubic spinel structure. The porosity values along values are good agreement with reported values [13- with the red-ox nature of Fe can be of much 14]. It is seen that the lattice parameter increases with importance in catalytic applications. Table 1. Inter-planar space, Lattice constant (a0), crystallite size (D), X-ray density (dx), bulk density (db) Sample name Angle measured at average peak 2 θ (degree) Ni 0.65Zn 0.35 Fe 2O 4 Ni 0.5Zn 0.5 Fe 2O D space in nm Lattice parameters (a in A 0 ) 0 Crystallite size (in nm), X-ray density (d x in g/cm 3 ) bulk density ( d B in g/cm 3 )) The value of B B(FW (WFHM) in rad From the table 1 it is observed that the average interplanar space between each plane was nm for x=0.5 and for x=0.65 displayed by XRD from peak position d-spacing. It is observed that the inter-planar space between each plane of the sample decrease with the increase in zinc concentration. This is probably due to the ionic radius of Zn (0.84 o ) greater than that of Ni (0.74A o ) atom. The line broadening of diffracted peaks is measure of particle size. The average nanocrystal size can be determined from the width of a diffraction peak using the Scherer equation. The ideal size for the powder diffraction lies in the range of 100 to 1000 nm. As a rough measure of the full width at half maximum (FWHM), we can take half the difference between the two extreme angles at which the intensity is Zero. Table 1 shows the result from the Scherer equation. From the above table the full width at maximum intensity, B is for X=0.65 and for X=0.5 displayed by XRD from peak position. It is possible to observe as the concentration of zinc increase the value of B also increase. As grain size decreases, hardness increases and peaks become broader. 3.2 SEM Analysis The microstructure analysis for both sample of ferrite was carried out using the high resolution SEM operated at 25KV, it is useful to study the microstructure form in different composition of ferrite and to identify the phase formed during sintering. It is also useful to interpret the size of the grain and grain boundaries. Fig 2 (a and b) shows scanning electron micrograph (SEM) for X=0.5 and X=0.65 respectively. An interesting observation of Fig.2(b) for X=0.65 is that the grain boundary areas are well eroded and the voids are large in size and number when we compare with Fig 2.(a) for X=0.5, this is due to Zn concentration in NZF also its grain size increase. Another observation is that the voids are homogeneously distributed throughout the volume and mostly they are open. It is also interesting to

4 Page No.7 note that the voids are filled and grains are well connected with each other. The sintered compositions were solidified as polycrystalline material [16]. Its average grain size is nm, observed in Fig 2 (a and b) the morphology of grain structure as seen from the SEM show maximum of cellular type nanocrystal due to less energy formation [17] and confirmed by XRD analysis. As we can be seen, the microstructure consists of relatively small in grain size. It is to be noted that small grains are preferred in ferrites [18].As oxidation advances faster in smaller grains; they lead to the acceleration of Fe 2+ to Fe 3+ transformation which results good ferrite properties. Figure 2. a) SEM patterns of Ni0.5Zn0.5 Fe2O4 b) SEM patterns of Ni0.65Zn0.35 Fe2O4 3.3.AC Conductivity Analysis As observed from Fig 3 for both sample up to the frequency 100KHz, it is observed that Ac conductivity value is zero at lower frequencies and the conductivity is independent of frequency up to 100KHz, but above this frequency the e line as shown in the figure of the (sample X=0.5) in Ac conductivity vs frequency exhibit small increase in the conductivity i.e however in higher frequency needed to observe from the previous direction in the upward direction, but the second sample (X=0.65) above that frequency of 100KHZ it follows thus the previous path, because AC electric conductivity in NZF depend on concentration of Zn. The polarization in ferrite has largely been attributed to the presences of Fe 2+ ions. Since Fe 2+ ions are easily polarisable, the larger the number of Fe 2+ ions the higher would be dielectric constant. The Ni ions strongly prefers the occupation of B-site and Fe 2+ ions partially occupies the tetrahedral sites (A sites) and B sites, while Zn strongly prefers the occupation of A sites, while the number of Zn ions decreases in the plot Ni ions increases. Therefore, local displacements (dielectric polarization) in the direction of external applied field (for electron) decreases and those in the opposite direction (for holes) increases. This explanation provides the basis of the increases in AC electronic conductivity as Ni ions substitution increases [19]. Figure 3. Ac conductivity of NixZn1-xFe2O4 for x=0.65 and X=0.65 KEYs; 1. The forward arrow shows sample X=0.5(the upper line) 2. The backward arrow shows sample X=0.5(the lower line) AC conductivity of NZF increases with the increase of frequency is independent of frequency up to 100 KHz. The concentration changes of Ni and Zn in Ni- Zn ferrite strongly affects its Ac conductivity or electrical property. As the concentration of Ni ions increases the Ac conductivity of the nanocrystal decreases due to domination of electronic conductivity than ionic conductivity since it is good electronic conductive material. Thus the magnetic properties of the ferrite since the Fe ions are having good magnetic properties the studies of magnetic properties will be discussed later in future work 4. Conclusions The synthesized NZF samples (X=0.5 and X=0.65) shows single phase cubic spinel structure. The microstructure of NZF sample was homogenous

5 Page No.8 throughout the entire matrix region with an average grain size 22-24nm. In both samples the x-ray density, bulk density and crystalline size, grain size and average inter planar space between plane increases with nickel content which in turns decreases the lattices parameter and porosity. This is due to large ionic radius of zinc ions. AC electric conductivity of NZF increases with the increase of frequency but at lower frequencies conductivity is independent up to 100 KHz. The concentration of Ni and Zn in Ni-Zn ferrite strongly affects its AC ionic conductivity or electrical property. As the concentration of Ni ions increases the Ac conductivity of the nanocrystal decreases due to electronic conductivity dominates over ionic conductivity. 5. References 1. Bozoroth. R., Physics. Review. 1076, 50, (1996). 2. Snoek. J.L. Philips Technolog Review. 583, 8, Neel. L, Annual. Physics. (Paris) 342, Snelling. E.C Soft ferrite property and Application Butterworth and Co (Publishers) Ltd., London Vado. R. T. And S. W. Material. Physics. Review, 43, 22, Murthy. V.R. K. And Sobhanadri, Journal. Physics. Statics. Solid. A, 647, 36, Mahalakshmi. J. Li. J. And Mahalakshmi.G Journal. Magnetic and Magnetic Material, Usha Varshney and Puri. D.K., IEEE Trans. Magn, 109, 25, John. L. Brechmans, and Sandals. R.C., IEEE Trans. Magn, 351, 13 (5), Ohmsha. N. Introduction to fine ceramics (Publisher) Ltd., Japan, Samokhvalov. A. A., Arbuzova. T. I., Simonova. M. I. and Fal kovskaya. L. D., Sov. Phys. Solid State 15, Lorrain.F, Venkataraju. S. Houle, Magneto-Fluid Dynamics, Springer Science Business Media, 1 Ed 45-48, (2006). 13. Leung. L.K, Evans. B. H. and Morrish. A. H., Physics. Review. 29,8, Harvey. R.L., Hegyi. I.J. and Leverenz. H.W., Physics. Review. 321, 11, Jankovskis. JSci. series 7, journal and Review, 548, Mustafa Hj, Roberts. A. F. And Welch. A. J. E., Journal. of Physics. 142, 15, Mustafa Hj, Physica Review Letter. 183, Sayned. El. and Raraksh Physics. Review. B 29, 8, Went. J. J. And Wijn. H. P. J, Physics, Review, 269, 82, 1951.