Elucidation of Structural and Morphological Properties of Cu0.6Ni0.4Fe2O4 Ferrite

Solid state reaction has been used successfully to prepare the spinel ferrite Cu0.6Ni0.4Fe2O4. The cubic structure of the sample was discovered by XRD crystal structure analyses. The Rietveld Refinement was used to further refine the XRD spectra, and all of the structure-related data were acquired, confirming the cubic (Fd-3m) structure. The calculated particle size was 91 nm. Five active Raman modes were visible in the Raman spectra, confirming the spinel structure. Raman analysis of the produced samples provided evidence of the lattice structure. Employing Fourier transform infrared (FTIR) spectroscopy, the sample formation was further confirmed. Compositional studies revealed that all the integral elements of the sample are present and there is no trace of impurity whereas morphological analysis infers the dominance of agglomeration phenomenon. The dielectric properties were investigated which were exceptionally good. Optical bandgap studies revealed wide band nature of the materials.


Introduction
Spinel cubic structure describes the oxide substance known as ferrites, which is primarily composed of Fe2O3.Spinel ferrites inherit wide variety of magnetic properties attributed to the occupation of tetrahedral (A-site) site by divalent metal ions and octahedral (B-sites) sites by trivalent metal ions.Performance in electrochemistry has considerably increased thanks to mixed metal oxides.Ferrites denoted by Spinel ferrites, MFe2O4 (where M = Cu 2+ , Mn 2+ , Co 2+ , Ni 2+ ), are intriguing materials as they exhibit distinguished optical, electrical and magnetic properties.In addition to this, they inherit various redox states and are electrochemically very stabile [1][2][3][4].
In the ferrite family, Nickel ferrite (NiFe2O4) is an indispensable member in which tetrahedral sites and octahedral sites have even distribution of Fe +3 ions.Attributed to their characteristic properties, nickel ferrites are vastly exploited in electronic device applications.As mentioned, they are mechanically hard, chemically very stable with higher electrical resistivity and permeability [5,6].On the other hand, copper ferrite (CuFe2O4) is also one of the most significant magnetic ferrites attributed to its unique magnetic, electric, thermal, and catalytic properties.Copper ferrite (CuFe2O4) has found variety of applications in modern device technology which includes ferro-fluid, colour imaging, gas sensing, and catalysis.Its spinel structure is cubic.Being partially inverse ferrite, CuFe2O4 exhibits an increase in magnetism with increasing Cu 2+ concentration [6][7][8].
It is anticipated that ferrite oxides (MFe2O4) will provide richer redox reactions than monometallic oxides, containing contributions from both M and Fe 2+ ions.Designing new ferritebased hybrids is a promising strategy for improving performance.The desired qualities inherited by a material are heavily influenced by synthesis procedure and the processing conditions which may include the preparation in open and inert atmosphere.In addition to this the fuel (organic) used for synthesis, sintering temperature rand the duration are other factors imposing the substantial impact on material properties.Mixed ferrites are formed by the combination of two metal ions with divalent features the ratio of which is subject to the variation [9][10][11].In the case of mixed spinel ferrites, cation distribution greatly influenced the surface characteristics making them catalytically active.Cu 2+ substitution in NiFe2O4 is thought to be a strong option for improving the electrical and magnetic properties.Cu 2+ ionic radius is 0.63Å, which is comparable to ionic radius of Fe 3+ (0.67Å) ion.Due to their same oxidation state, Cu 2+ is thought to have an impact on the dielectric and magnetic characteristics without changing the crystal structure [10][11][12][13][14]. Taking into consideration, the technological importance of Cu 2+ and Ni 2+ ferrites and their mixed state, we tried a mixed ferrite of the type Cu0.6Ni0.4Fe2O4.The synthesis process exploited was ceramic and the physical properties discussed include structural, morphological and dielectric properties.

Experimental Details
Synthesis: By using the traditional method of solid-state reaction in ceramic fabrication, the Cu0.6Ni0.4Fe2O4sample was created.Manganite (Cu0.6Ni0.4Fe2O4)was made from the beginning analytic grade components NiO2, CuO, and Fe2O3 by mixing them in stoichiometric quantities.After being ground for five hours, the mixture was calcined in the air at 1000 °C for four hours.The calcined powder was ground for five hours again to get fine powder and was subjected to calcination temperature of 1150 °C for four hours in order to facilitate the reaction of un-reacted material.Under pressure of 8 tonnes produced by a hydraulic press, the fine powder was transformed to pellet (10 mm in diameter and 1 mm in width) and then sintered in air at 1250 °C.The pallet was created for the purposes of SEM/EDAX and Raman characterization.Characterizations: We determined the crystal structure of Cu0.6Ni0.4Fe2O4ferrite powder exploiting X-ray diffraction technique employing X-ray diffractometer (Bruker D8-Advance) with CuKα1 (λ=1.5406Å)radiation with 0.02 o step size.The XRD data underwent Rietveld refinement using the FullProf programme.Raman spectrum was obtained on micro Raman system, Jobin Yvon Horiba LABRAM-HR visible (400-1100 nm), with argon (488 nm) as the excitation source.SEM image and EDAX spectrum was obtained using instrument model JEOL JSM-5600 and energy-dispersive spectrometer, model INCA Oxford respectively.FTIR spectrum was recorded using Perkin Elmer FT-IR/FIR spectrometer.

Results and Discussion
XRD Analysis: To emphasize on the crystal structure of Cu0.6Ni0.4Fe2O4ferrite sample, X-Ray diffraction technique was used.The diffraction data was arranged and plotted as Figure 1.The study of the XRD spectrum of the sample has revealed the acquiring of cubic crystal structure (Fd-3m) [15,16].
Using Scherer's equation, which takes into account the X-ray wave length (λ=1.5406Å), the shape factor, the Bragg's angle (2θ), and the width mum (FWHM) of diffraction peaks, the calculated crystallite size on average was found to be 91 nm.The diffraction peaks are sharp which infers that the sample is highly crystalline whereas FWHM of these diffraction peaks are narrow which indicates the large size of the particles.
The Rietveld refinement suggested by Figure 2 was applied to the XRD spectrum.The refinement validates the prepared space group and acquired structure of the sample.The various structural parameters obtained include lattice parameter (a) =8.987Å, density (ρ) = 4.799 Å, volume (V) = 582.692Å 3 , Chi square (χ 2 ) = 2.56 and goodness of fit (GoF) = 2.09.All these confirm the revelations of XRD analysis.Raman Spectral Analysis: Five Raman active (A1g + Eg +3T2g) modes were discovered at room temperature in the Raman spectrum depicted as Figure 3 of the spinel Cu0.6Ni0.4Fe2O4compound, which has acquired cubic structure (Fd-3m).The quasi-molecular model of the spinel structure explains well the mobility of the O-ion and tetrahedral A-site ions in these active Raman modes of vibration.The Raman peaks are all asymmetric.The Fe 3+ and Ni 2+ /Cu 2+ are thought to be arranged over the A and B sites [17,18].
The symmetric stretching of oxygen atoms along Fe-O and Ni/Cu-O links in the tetrahedral coordination causes the A1g [701 cm -1 ] mode.The modes of vibrations Eg [329 cm -1 ]( symmetric) and F2g(3) [570 cm -1 ] (asymmetric) results from bending of oxygen with respect to the metal ion.The asymmetric F2g(2) [477 cm -1 ] comes into the existence from stretching of Fe (Ni/Cu) and O. F2g(2) and F2g(3) are the octahedral group vibrations.The translational movement of the tetrahedron causes F2g(1) [199 cm -1 ] mode of vibration.Each of the five Raman peaks has a shoulder on the side with lower  energy.At the microscopic level, Cu0.6Ni0.4Fe2O4can be considered to be composed of two sublattice and the B-sites occupied by Fe 3+ and Ni 2+ ions in an ordered fashion [17][18][19].

Compositional and Microstructural Studies:
The technique of energy dispersive X-ray analysis (EDAX) allows us to identify the effect of the dopants in trace amounts while also verifying the    composition of the sample.In this regard, we used the EDAX approach to characterize our Cu0.6Ni0.4Fe2O4sample for compositional verification.The EDAX spectrum of the sample under examination is shown in Figure 5(a).A careful examination reveals that every part of the compound and its composition has been preserved, and that within the constraints of the experiment, there has been no loss of any essential components.The composition of the sample is revealed from intensity of the peaks where higher intensity arises according to the concentration of the element.The opportunity to evaluate the material under observation for further physical qualities and the impact of dopants and phases is thus made possible by this exact characterization [22,23].SEM abbreviated as scanning electron microscope was exploited to emphasize on microstructure and morphology of the sample.The SEM image of the sample is shown as Figure 5(b).A close look at the micrograph reveals that the sintering at higher temperatures has given rise to the large size of the grains attributed to the mass transport facilitated by higher temperature.According to the micrographs, the crystals are well separated from one another and there isn't a definite grain boundary.The FESEM images show that the agglomeration phenomena predominates [22][23][24].ImageJ software was used to calculate the average particle size, which came out to be 1.13 μm.Dielectric Properties: Dielectric permitivity of the Cu0.6Ni0.4Fe2O4ferrite was investigated at room temperature in the frequency range of 100Hz-1MHz and is shown as the inset of Figure 6.The usual tend of dielectric response as a function of frequency was observed.It is high at lower frequencies and decreases abruptly as frequency increases.In the higher frequency range, the dielectric permittivity does not respond to the applied field.This behaviour is attributed to the fact that electronic exchange between metal ions does not obey the applied field frequency.The higher value of dielectric constant at low frequency arises from the piling up of charge carriers at the grain boundaries which enhances thereby enhances the extent of polarization and hence the dielectric constant.The abrupt decrease in the dielectric constant arises from the charge reversal within the conducting grains from the grain boundaries [25].Figure 6 further reveals the dissipation of the material as the dielectric loss.The dielectric loss follows the trend followed by the dielectric constant as response to the applied field.The loss arises from the lattice defects, crystal inhomogeneities and the impurities [25,26].Optical Bandgap studies: The ferrite sample reported here has been investigated for optical band gap.The diffuse reflectance UV-Vis spectroscopy exploited for the optical bandgap determination has been presented as Tauc's plot displayed as Figure 7.The extrapolated sharp edge makes an intercept at 1.95 eV which is actually the optical band gap of the as synthesized sample [27].

4.
Conclusions Spinel Ferrite Cu0.6Ni0.4Fe2O4, a substance made by a solid state reaction, with well-defined structural characteristics was addressed.Rietveld refinement has proven that the Cu0.6Ni0.4Fe2O4crystallises into the cubic structure (Fd3m).Via the demonstration of the distinctive Raman modes of vibration, the lattice structure is confirmed by the Raman spectrum.The FTIR spectrum also showed the desired oxide production.While agglomeration is clearly visible in SEM, which shows substantial diffusion from grown average particle size, EDAX suggests that the investigational materials' integral components have been retained.The dielectric properties are quite good with high dielectric permittivity and low value of dielectric dissipation.Optical band of the order of 1.95 eV has been established for the ferrite sample under investigation.