Pure and doped nano-Li-ferrite spinels were prepared by the sol-gel auto-combustion technique. The prepared ferrites were pelleted and heat treated at different temperatures. Structural characterization was carried out on the as-prepared samples and also on the heat-treated samples using X-ray diffraction (XRD). The studies confirmed the formation of single phase with spinel structures in all the samples. The crystallite size of the samples evaluated from XRD data was found to be 17-24 nm. Scanning electron microscopic photomicrographs revealed the microstructures and the grain size of these nanoferrites. The room-temperature dielectric constant and dielectric loss tangent, tan δ were measured as a function of frequency in the range 100 Hz-1 MHz. These nanoferrites showed the normal dielectric dispersion behaviour. The observed dielectric constant and dielectric loss tangent were found to be much lower than those measured on substituted Li-ferrites prepared by the conventional ceramic method. The results obtained were discussed in the paper.
Li–Ni–Co ferrite samples with compositional formula Li[Formula: see text]Ni[Formula: see text]Co[Formula: see text]Fe[Formula: see text]O4 with [Formula: see text] ranging from 0.00 to 0.1 in steps of 0.02 were prepared by sol–gel method. X-ray diffraction (XRD) analysis confirmed the formation of single phase with spinel structure in all the samples. The lattice constant evaluated from XRD data was found to increase with increase of Co[Formula: see text] substitution and crystallite size was observed in the range of 30–59 nm. The microstructure of the samples was studied by using scanning electron microscopy (SEM). Nanocrystalline nature of ferrites was also confirmed by transmission electron microscopy (TEM). [Formula: see text]–[Formula: see text] measurements were made using a vibrating sample magnetometer and hysteresis parameters such as saturation magnetization and coercivity were obtained for all compositions. The frequency variations of initial permeability and permeability loss showed a dispersive behavior for all compositions and an increase in initial permeability is observed with increase of Co[Formula: see text] substitution. The results obtained and mechanisms involved are discussed in the paper.
Ni substituted Li-Zn ferrites with compositional formula Li 0.4-0.5x Zn 0.2 Ni x Fe 2.4-0.5x O 4 where 0.02 ≤ x ≤ 0.1 in steps of 0.02 was fabricated by using citrate precursor method. X-ray diffraction was used to confirm the spinel phase. The dielectric constant was investigated as a function of composition, frequency and temperature. Room temperature dielectric constant showed a decrease with addition of Ni 2+ ions. It was explained in terms of space charge polarization and koops two layer model. The variation in dielectric constant with frequency showed dispersion. Variation of dielectric constant with temperature was studied at different frequencies and an increase was observed as temperature rises. The possible mechanisms responsible for the above behavior are explained.
The properties of lithium ferrites are very sensitive to chemical composition, synthesis method, and sintering techniques. Li-Ni-Co ferrites with compositional formula Li 0.45−0.5x Ni 0.1 Co x Fe 2.45−0.5x O 4 , where 0.00 ≤ x ≤ 0.1 in steps of 0.02 were prepared by chemical sol-gel method and sintered by microwave sintering technique. The x-ray diffraction patterns confirmed the formation of single phase with spinel structure in all the samples. The structural parameter viz. lattice constant, crystallite size, and x-ray density for these samples were studied and compared with those measured from samples of similar composition prepared by the sol-gel method and sintered by conventional sintering technique. Enhancement in the magnetic properties like Curie temperature, hysteresis parameters was observed by employing sol-gel synthesis combined with microwave sintering. The results obtained and mechanisms involved are discussed in the paper.
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