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  • 1. Pathan Amjadkhan Noorkhan, Sangshetty Kalayne / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 4, June-July 2012, pp.681-685 Synthesis, Characterization Ac Conductivity Of Nickel Ferrite Pathan Amjadkhan Noorkhan1 and Sangshetty Kalayne2* 1 Department of Physics, Singhania University, Pacheri- Bari, JhunJunnu, Rajasthan 2 Department of Physics, Bheemanna Khandre Institute of Technology (REC), Bhalki, Bidar, Karnataka, India.Abstract Nickel ferrites were synthesized by involved in the changes caused by the addition ofemploying sol gel technique at 6000C sintering impurities provides information on which the reliabletemperature. The prepared samples were formulation of ferrites suitable for specificcharacterized by XRD for structural analysis applications can be based.indicates that the percentage of iron ions in B site Ceramic method [4, 5] for the preparation ofincreases, the intensity of the (222) peak increases. ferrites places certain limitations such as, requirementThis indicates that the structural changes of the of relatively high firing temperature and more timeNiFe3O4, arise from the shifting of ions between A which may cause the evaporation of certain elementsand B sites. The morphology was studies using like Zn [6] leading to the formation of chemicallySEM and found that morphology is more favorable inhomogeneous material [7]. In case of Ni Zn ferrites,for charge transportation in ferrites. The nickel zinc volatilization at high temperature increases theferrite (NiFe3O4) shows high σac conductivity due to electron hopping and reduces resistivity [8, 9]. Duringdipole polarization. The high value of dielectric milling and grinding, there may be a loss of someconstant of the sample NiFe3O4 is because of material, which leads to nonstoichiometry in the finalstructural changes associated with the nickel ferrite product [10]. Also the ferrites prepared by ceramicwhen the grain size is reduced to nanometer order. method have the larger particle size and low density. Chemical method overcomes these limitations ofKey words: Nickel ferrite, X-ray diffraction, Ac ceramic method and makes it possible to prepare theconductivity, dielectric constant. homogeneous, dense and smaller particle size ferrite [11, 12].Introduction Among the spinel type ferrites, nickel ferrite Mixed nickel ferrites having high Curie is a suitable material for microwave applications [13].temperature and different magnetization form an It is noted for its high Curie temperature and goodimportant class of magnetic materials used in many temperature stability of saturation magnetization [14].technological applications [1]. Those characteristics The properties of nanoparticles are interestingare in close connection with the magnetic structure, due to the presence of very large and highly disorderedwhich is dependent on the magnetic cations, their grain boundaries. Because of the peculiarities of thedistribution and concentration. Ni–Zn ferrites, which grain boundaries nanomaterials exhibit unusual and/orhave a high resistivity and low eddy current loss, are enhanced dielectric properties. In this present paperused in high frequency and pulse field applications. authors report the synthesis, characterization, acThis system has a cubic spinel crystal structure with conductivity and dielectric properties of nickel ferrite.the unit cell consisting of eight formula units of theform Znx 2+Fe1−x 3+[Ni1−x 2+Fe1+x 3+]O4 2−. The 32 Experimentaloxygen anions per unit cell form a face centered cubic All Chemicals used were analytical gradecage, while the metallic cations occupy interstices. (AR). The nickel chloride (purity 99.99%) andThe metallic cations outside the bracket occupy the dehydrated ferric chloride were procured and weretetrahedral sites (A-sites) comprising tetrahedral used as received.sublattice while those metallic cationsenclosed by thebracket occupy octahedral sites (B-sites) comprising Nickel chloride and ferric chloride are mixedthe octahedral sublattice [2-3]. The properties of in calculated stoichiometric with oxalic acid inferrites are very sensitive to the method of preparation equimolar ratio so as to form nickel ferric oxalateand the amount and type of substitution. The addition precursor. The precursor is then filtered and dried atof impurities induces changes in the defect structure 500C to achieve constant weight. The precursor isand texture of the crystal. An understanding of the mixed with polyethylene glycol (PEG) in the ratio 1:5mechanisms and is ignited. The combustion propagates throughout the precursor. After completion of combustion nickel 681 | P a g e
  • 2. Pathan Amjadkhan Noorkhan, Sangshetty Kalayne / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 4, June-July 2012, pp.681-685ferrite (NiFe3O4) is formed. The nickel ferrite is from the full width at half maximum (FWHM) valuessonicated in acetone media for 20min and then of (311) reflection of the X-ray diffraction usingcalcinated at 6000C to remove the impurities. Finally, Scherrer’s equation (Klug and Alexander 1954).fine graded nanosized nickel ferrite particles areformed. The pellets of 10 mm diameter are preparedwith thickness varying up to 2 mm by applyingpressure of 10 Tons in a UTM – 40 ( 40 Ton Universaltesting machine). For temperature dependentconductivity and sensor studies, the pellets are coatedwith silver paste on either side of the surfaces to obtainbetter contacts.The X-ray diffraction (XRD) pattern of the NiFe3O4was recorded at room temperature by employing an x-ray powder diffractometer (Rigaku Miniflex) withCuK radiation (=1.5405A0) in the 2 (Braggangles) range (20≤ 2 ≤100) at a scan speed of 0.50 Figure 1. Shows the XRD pattern of NiFe3O4 at 600oCminute-1. sintering temperature The percentage transmittances for the entire Figure 1show the XRD pattern of NiFe3O4 at 600oCsample are measured from 300 to 4000 cm−1. The sintering temperature. It was reported that nickelSEM images of polyaniline cadmium oxide ferrite deviates from its inverse spinel structure withcomposites were recorded using Philips XL-30 the reduction in grain size by Ponpandian et al. When(ESEM) scanning electron microscopy. The set up the grain size of nickel ferrite is reduced to nanometerused for measuring ac conductivity is Hioki 3050 order, some percentage of nickel ions get shifted fromimpedance analyzer, which is in turn interfaced to the B site to A site at the same time shifting an equalcomputer. number of iron ions from A to B site. The percentage of iron ions in B site increases with the reduction inResults and discussion grain size. This shifting of ions causes changes in An analysis of the dielectric properties of the XRD pattern also. As the percentage of iron ions in BNiFe3O4 has been carried out using impedance site increases, the intensity of the (222) peak increases.spectroscopy on application of a small a. c. signal This indicates that the structural changes of theacross the sample cell with blocking electrode NiFe3O4, arise from the shifting of ions between A and(stainless steel). Complex impedance parameters (i.e., B sites. This shifting of ions is assumed to becapacitance, dissipation factor, impedance, phase prominent near the surface layers. Because theangles parameters) were measured with a computer- arrangement of ions in the core region of nanoparticlescontrolled impedance analyzer (HIOKI LCR Hi- is identical with that in bulk crystals, while the alteredTester, Model: 3532, Japan). A. C. conductivity has structure due to the reduction in the size is confined tobeen evaluated from dielectric data in accordance with surface layers. As the size of a particle is reduced thethe relation: surface to volume ratio increases and the number of ac = 0rtan iron ions in B sites increases. where r = C/C0 is the relative permittivity,tan= tangent loss factor, C = vacuum capacitance 0of the cell. The real and imaginary part of permittivityand modulus was calculated from the relation Figure 1 shows the XRD patterns of NiFe3O4at600oC sintering temperature. The peaks in thespectra agreed closely with the data in the ICDD file(card number 10-325) for NiXFeX-1O4 indicating thatthe samples synthesized were nickel ferrite. Thediffraction pattern of the samples showed broad peakswhen compared with the bulk nickel ferrite. Theaverage grain sizes of the particles were calculated 682 | P a g e
  • 3. Pathan Amjadkhan Noorkhan, Sangshetty Kalayne / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 4, June-July 2012, pp.681-685Scanning Electron Microscope (SEM) The ac conductivity ac was determined using the formula 1 ac = (3)  ac When field is applied to a dielectric, the polarization of the dielectric takes place. The dielectric displacement found in a dielectric material when subjected to an alternating field (E) is not in phase. Hence the dielectric constant is a complex quantity and is expressed as * =  + i (4) where  is the real part (denoted as r for ourFigure 2. Shows that the SEM image of NiXFeX-1O4 at discussions) and  is the imaginary part, 600oC sintering temperature In the rectangular coordinate system, the real and imaginary part of the impedance was calculated byFigure 2 (a) shows that SEM image of nickel ferrite at600oC sintering temperature. It is clearly observed formulaefrom the image they are agglomerated, highly Z = |Z | cos  (5)branched and porous in nature. The average grain sizewas calculated by using line intercept formula and it is When the complex impedance plane plotsfound to be 0.21µm. were obtained, where a semicircle, is obtained the relaxation time was calculated using the relation =1.AC Conductivity Using the values of equivalent parallel -4capacitance (Cp), dissipation factor (D), phase angle 1.0x10(δ) and parallel equivalent resistance (Rp) that are NiFe3O4recorded by the LCR meter at selected frequency -5range (f), the ac conductivity (ζac), dielectric constant 8.0x10(ε΄) and dielectric loss (tan δ) parameters have beencalculated [15]. -5The resistance ac of the samples was found by using 6.0x10the equation. ac S/cm -5 R x A 4.0x10ac = P (1) t -5 Where Rp, the resistance of the sample is 2.0x10given by, 0.0Rp = Z 1  tan  2 (2) 2 3 4 5 6 The a.c conductivity is frequency and 10 10 10 10 10temperature dependent entity. The electrical Frequency (Hz)conduction is a thermally activated process andfollows the Arrhenious law Figure 3. Shows the variation of ζac of NiFe3O4 as a ac = 0 e where ac conductivity, 0 -Ea/KT function of pre exponential factor, Ea is the activation energyand K is Boltzmann constant. 683 | P a g e
  • 4. Pathan Amjadkhan Noorkhan, Sangshetty Kalayne / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 4, June-July 2012, pp.681-685Figure 3 shows the variation of ζac of NiFe3O4, as afunction of frequency. The conductivity of nickel Figure 4 shows the variation real permittivity () offerrites is increases with increase in frequency. The nickel ferrite of various composition as a function ofnickel ferrite (NiFe3O4) shows ζac conductivity of 1.0 x logarithmic frequency. It is found that in all these10-4 S/cm. This is may be attributed to the dipole nickel ferrite compositions, as frequency increases,polarization i.e., the rotation of dipoles between two dielectric constant decreases up to the frequency rangeequivalent equilibrium positions is involved. It is the of 104 Hz and after that it remains constant for furtherspontaneous alignment of dipoles in one of the increasing in frequency. The strong frequencyequilibrium positions that give rise to the nonlinear dispersion of permittivity is observed in the lowpolarization behavior of this composition. frequency region followed by a nearly frequency This behavior of NiFe3O4 obeys the universal independent behavior above 10 kHz. It is observedpower law, (ω)= (ω)n (the solid line is the fit  that Debye type relaxation mechanism is responsibleto the expression), where r0 is the dc conductivity for higher value of NiFe3O4.(frequency independent plateau in the low frequencyregion), A is the pre-exponential factor, and n is the 0.8 tan deltafractional exponent between 0 and 1 [16]. Oncrystallization, the conductivity spectrum remains 0.7similar as that of the nickel ferrite except dispersion inthe low frequency region, where the deviation from 0.6dc (plateau region) is more prominent. The deviation 0.5from dc (plateau region) value in the conductivityspectrum (in the low frequency region) is due to the tan 0.4electrode polarization effect. The values of , A, andn were obtained by fitting the (ω) to 0.3(ω)= (ω)n. The overall behavior of ac follows the universal dynamic response, which has 0.2widely been observed in disordered materials likeionically conducting glasses and also doped crystalline 0.1solids, and is generally believed to be reflected in the 0.0mechanism of charge transport behavior of chargecarriers. 2 3 4 5 6 10 10 10 10 10 Frequency (Hz) Figure 5. Shows the variation of dielectric constant as a function of frequency of NiFe3O4 Figure 5 shows the variation of dielectric constant as a function of frequency for NiFe3O4. The high value of dielectric constant of the sample NiFe3O4 may be explained on the basis of the structural changes associated with the nickel ferrite when the grain size is reduced to nanometer order. Nickel ferrite crystallizes into a cubic close-packed arrangement of oxygen ions. It belongs to the class of ferrites with an inverse spinel structure having structural formula, Fe3+[Ni2+Fe3+]O4. The metal ions given in the square bracket are called octahedral (B site) ions and that outside the square bracket are called tetrahedral (A site) ions. The nickel ions (Ni2+) together with half of the iron ions (Fe3+) occupy the B site and the remaining half of the iron ions reside in A site. The presence of Ni2+ and Ni3+ ions gives rise to p-type carriers (holes) whereas Fe2+ and Fe3+ ions produce n-type carriers (electrons). Figure 4. Shows the variation real permittivity () of Therefore, both electrons and holes that are present in nickel ferrite as a function of frequency. the B sites are due to the presence of Ni and Fe ions. 684 | P a g e
  • 5. Pathan Amjadkhan Noorkhan, Sangshetty Kalayne / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 4, June-July 2012, pp.681-685Since only iron ions are present in A sites, electronsare the carriers in A sites. The distance between the Referenceions in A sites (0⋅357 nm) is larger than the distance [1] D. Vladikova, H. Yonchev, L. Ilkov, S. Karbanov,between the ions in B site (0⋅292 nm). Also, the J. Magn. Magn. Mater. 78 (1989) 420degree of covalency for the A site ions is higher than [2] A.M. El-Sayed, Materials Chemistry and Physicsthat of the B site ions. All the above factors result in a 82 (2003) 583–587high activation energy for the A sites compared to the [3] J . S . Baijal, deepika kothari and sumitraB sites. Hence, in ordinary nickel ferrite with an phanjoubam, Proceedings of ICF-5 (1989) pp.inverse spinel structure the electron movement in B 371.sites dominates compared to that in A sites. [4] J . Smit, “Magnetic Properties of Materials” (Mc Grow-hill Book Company, New York, 1971).Conclusion [5] K. J . Standley, “Oxide Magnetic Materials” Nickel ferrite (NiFe3O4) is prepared by (Oxford UK Clarendon, 1972).employing sol gel technique. XRD studies revels that [6] M. I . Rosales, E. Amano, M. P . Cuatle and R.the percentage of iron ions in B site increases with the Valenzuela, Mater. Sci. Engng. B49 (1997) 221. [7] K. C. Patil, S . Sunder manoharan and D.reduction in grain size. This shifting of ions causes Gajpathy, Marcel Deekar 1 (1990) 473.changes in XRD pattern also. As the percentage of [8] A. Verma, T. C. Goel, R. G. Mendiratta and R. G.iron ions in B site increases, the intensity of the (222) Gupta, Journal of Magnetism and Magneticpeak compared to that of the (220) peak increases. Materials 192(1999) 271.From the SEM image, it is observed that the granular [9] A. Verma, T. C. Goel, R. G. Mendiratta and P .size increases with increase in percentage of Ni and Kishan, ibid. 208 (2000) 13.sintering temperature. The nickel ferrite shows high [10] C. N. R. Rao and J . Gopalkrishnan, “Newζac conductivity of 1.3 x 10-4 S/cm due to attribution of Directions in Solid State Chemistry” (Cambridgethe dipole polarization. The high value of dielectric Univ. Press, (1989). [11] Giannakopoulou T, Kompotiatis L,constant of the sample NiXFeX-1O4 is because of Kontogeorgakos A and Kordas G 2002 J. Magn.structural changes associated with the nickel ferrite Magn. Mater. 246 360when the grain size is reduced to nanometer order. [12] Goldman A 1990 Modern ferrite technology (New York: Van Nostrand Reinhold) p. 71 [13] Gopal Reddy C V, Manorama S V and Rao V J 1999 Sensors and Actuators B55 90 [14] Gotic M, Czako-Nagy I, Popovic S and Music S 1998 Philos. Mag. 78 193 [15] Green J J, Waugh J S and Healy B J 1964 J. Appl. Phys. 35 1006 [16] Han K C, Choi H D, Moon T J and Kim W S 1995 J. Mater. Sci. 30 3567 685 | P a g e