Copper-substituted Ni-Zn nanoferrite system having the composition of Ni 0.65 Zn 0.35−x Cu x Fe 2 O 4 (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25) has been prepared by autocombustion method. Structural and magnetic characterizations were done on the as-prepared powders while the dc electrical conductivity measurements were studied on pellets sintered at 900 • C. X-ray diffraction measurements of all the samples showed a single spinel phase. The lattice parameter has been found to decrease with increasing Cu, and this variation in the spinel unit cell is ascribed to the difference in the ionic radius of Cu 2+ and Zn 2+ ions. The average crystallite size was determined using the Scherrer equation. The dc electrical resistivity of nanocrystalline starting composition Ni 0.65 Zn 0.35 Fe 2 O 4 was few orders of magnitude higher than the bulk Ni 0.65 Zn 0.35 Fe 2 O 4 prepared by conventional ceramic method. However, Curie's temperatures and dielectric constant were decreased with increasing copper concentration. The observed variation in dc electrical resistivity and activation energy for conduction with Cu 2+ substitution is attributed to changes in the microstructure , structural defects, and hopping mechanism.
Nanocrystalline lithium substituted Ni–Zn ferrites with composition Ni[Formula: see text]Zn[Formula: see text]Li[Formula: see text]Fe2O4 ([Formula: see text] = 0.00–0.25 in steps of 0.05) were synthesized by the citrate gel auto-combustion method and were sintered at 1000[Formula: see text]C for 4 h in air atmosphere. The structural, dielectric, impedance spectroscopic and magnetic properties were studied by using X-ray diffraction, impedance analyzer and vibrating sample magnetometer respectively. The X-ray diffraction patterns confirm that all samples exhibit a single phase cubic spinel structure. Suitable cation distribution for all compositions has been proposed by using the X-ray diffraction line intensity calculations and the theoretical lattice parameter for each composition was observed in close agreement with the experimental ones and thereby supporting the proposed distribution. An increase in the saturation magnetization was observed up to [Formula: see text] = 0.10 level of Li[Formula: see text] substitution and thereafter magnetization reduced for higher concentrations to the highest level of Li[Formula: see text] substitution. The dielectric constant and the DC resistivity of Ni–Zn–Li ferrites were noticed to decrease with increase in the Li[Formula: see text] ion concentration. The impedance spectroscopic studies by using the Cole–Cole plots were studied in order to obtain the relaxation time, grain resistance and grain capacitance. AC conductivity initially remained almost independent of frequency for lower frequencies and thereafter for higher frequencies the AC conductivity increased with increase of Lithium concentration.
Polycrystalline Cu substituted Ni–Zn ferrites with chemical composition Ni[Formula: see text]Zn[Formula: see text]-Cu[Formula: see text]Fe2O4 (x = 0.00 to 0.25 in steps of 0.05) have been prepared by citrate gel autocombustion method. The samples for electrical properties have been sintered at 900[Formula: see text]C for 4 h. The X-ray diffraction patterns of all samples indicate the formation of single phase spinel cubic structure. The value of lattice parameter is decreases with increasing Cu concentration. The estimated cation distribution can be derived from X-ray diffraction intensity calculations and IR spectra. The tetrahedral and octahedral bond lengths, bond angles, cation–cation and cation–anion distances were calculated by using experimental lattice parameter and oxygen positional parameters. It is observed that Cu ions are distributed in octahedral site and subsequently Ni and Fe ions in tetrahedral site. The grain size of all samples has been calculated by Scanning Electron Microscopy (SEM) images. The variations in DC electrical resistivity and dielectric constant have been explained on the basis of proposed cation distribution.
In this study, nanocrystalline ferrite powders with the composition Ni 0.5 Zn 0.5 Fe 2 O 4 were prepared by the autocombustion method. The obtained powders were sintered at 800 o C, 900 o C and 1,000 o C for 4 h in air atmosphere. The as-prepared and the sintered powders were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and magnetization studies. An increase in the crystallite size and a slight decrease in the lattice constant with sintering temperature were observed, whereas microstrain was observed to be negative for all the samples. Two significant absorption bands in the wave number range of the 400 cm −1 to 600 cm −1 have been observed in the FT-IR spectra for all samples which is the distinctive feature of the spinel ferrites. The force constants were found to vary with sintering temperature, suggesting a cation redistribution and modification in the unit cell of the spinel. The M-H loops indicate smaller coercivity, which is the typical nature of the soft ferrites. The observed variation in the saturation magnetization and coercivity with sintering temperature has been attributed to the role of surface, inhomogeneous cation distribution, and increase in the crystallite size.
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