Effect of Al3+ ion substitution on the structural, electrical properties of spinel nickel NiFe2O4) ferrite Nanoparticles

Sanjeet Kumar Paswan* and Lawrence Kumar
Department of Nanoscience and Technology, Central University of Jharkhand Ranchi-835205, India


Transition metal spinel-structured nickel ferrite (NiFe2O4) exhibits an inverse spinel structure, which is a collinear ferrimagnet. A collinear ferrimagnet means that its magnetic moment is explained in terms of the Neel collinear two-sublattice model of ferrimagnetism. It is a centrosymmetric soft ferrimagnetic material with a magnetic ordering temperature that is far above room temperature. Its Curie transition temperature has been reported to be ~ 800 K. It possesses a high electrical resistivity, good mechanical hardness, and excellent chemical, thermal, and structural stability. This material has a wide range of applications such as high-frequency microwave devices and biomedical applications. The addition of trivalent ions, that is, non-metal elements such as Al3+ ( diamagnetic) for Fe3+ in NiFe2O4 ferrite, influences the structural, optical, and electrical properties of the system. The Effect of Al3+ ion substitution on the structural, optical, and electrical properties of spinel nickel ferrite (NiFe2O4) nanoparticles with the general formula NiFe2-XAlXO4 (where x = 0.1, 0.2, and 0.3) via the citrate – gel method. The samples were characterized using XRD, Raman spectroscopy, UV-Vis spectroscopy, TGA, FESEM, EDAX, FTIR, TEM, SAED patterns, and an LCR Impedance Analyzer. The XRD patterns revealed that the prepared NiFe2-XAlXO4 ferrite has a mixed spinel structure that is polycrystalline in nature and possesses a single-phase cubic spinel structure. By employing the full pattern fitting of the Rietveld method using the FullProf program, the exact coordinates of atoms, unit cell dimensions, atom ion occupancy, degree of inversion, crystallite size, and residual microstrain were determined and found to have a cubic structure with the Fd-3m space group. The cation distribution was obtained from the XRD and Rietveld methods, and the variation in the cation distribution was discussed on the basis of site preference, size, and valence of the substituting cations. The lattice parameter, X-ray density, particle size, and lattice strain decreased with increasing A13+ ion content, whereas the specific surface area and porosity increased with increasing A13+ ion content. Metal oxygen stretching, metal cation active vibration modes, and bending vibrations were confirmed through Raman spectra; there were five Raman active modes, A1g + E1g + 3 T2g of the motion of O2- ions and both the A-site and B-site ions. The Raman frequency trend with Al3+ ion content shows a blue shift for all modes, which is consistent with the replacement of Fe3+ by the lower mass Al3+. The energy band gap (Eg) calculated from UV-Vis spectra varies from 2.76 eV to 2.00 eV with the aluminium concentration x. TGA was performed to determine the low temperature, revealing that the material was thermally stable above 7000C. The FESEM images show a nanocrystalline morphology with small particle agglomerations of spherical structures and shapes. EDAX indicates the presence of Ni, Al, Fe, and O in the samples. The IR spectra showed two major absorption bands. The high-frequency bands ‘ν1’ is assigned to the tetrahedral and the low-frequency bands ‘ν2’ is assigned to the octahedral complex. The TEM images show that the particles are spherical in nature. The SAED pattern shows the lattice fringes (111), (220), (311), (222), (400), (422), and (511), which describe the spinel crystal structure of the NiFe2-XAlXO4 ferrite nanoparticles. The Impedance analyzer, which is used to determine the dielectric and electrical properties and the electrical conduction are explained on the basis of the hopping mechanism. The frequency-dependent dielectric properties of these spinel ferrites were studied at room temperature by measuring the AC conductivity (σac), dielectric constant, and dielectric loss tangent (tan δ). The dielectric constant and Dielectric Loss factor decrease with an increase in Al3+ ion concentration, and the phenomenon of dielectric dispersion has been explained on the basis of space charge polarization according to Maxwell–Wagner’s two layers of model and Koop's phenomenological theory and AC conductivity. The AC conductivity shows an increasing trend with an increase in Al3+ ion concentration, which indicates the blocking of the conduction mechanism between Fe3+ and Fe2+ ions, and it follows the super linear power law, that is, universal features of the distorted disordered matter. The observed results can be explained by their composition.



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