Relaxation and Dielectric Characteristics of Zn Substituted Copper-gallate Ferrite

The dielectric permittivities(ε'&ε")and dielectric loss tangent(tan)are studied for the prepared samples CuFe2O4 and Cu1-xZnxGa0.1 Fe1.9 O4 spinel ferrites with (0.0≤x≤0.5)from room temperature up to 700K in the frequency range(102～105Hz).Dielectric anomaly at the transition temperature Tc is pronounced in the relations of dielectric permittivitties with temperature where,the obtained Tc is found to decrease linearly with increasing Zn concentration.The relation of tan with frequency at different temperatures shows relaxation spectra where the relaxation time and the maximum frequency of the hopping conduction mechanism are determined.The variation of(ε',ε"and tanδ)with frequency and temperature displays a strong dependence on both gallium and zinc concentrations.The results are explained in light of the cation-anion-cation and cation-cation interactions over the octahedral sites in the spinel structure.     

Structural and Magnetic Studies of Rare-Earth Substituted Nickel Ferrites

Polycrystalline ferrites NiFe₂O₄ and NiFe_1.99R_0.01O₄ (R=Sm, Gd, Eu, and La) samples were prepared by usual ceramic method. The structural and the magnetic properties of the samples were characterized by X-ray powder diffraction (XRD), Mössbauer Effect (ME) spectroscopy, and vibrating sample magnetometer (VSM). Indexed XRD patterns confirm the formation of pure cubic spinel phase. The lattice parameters (a) of the rare earth (R) doped samples were smaller than that of the pure Ni-ferrite. Mössbauer effect spectroscopy was used to study the distribution of cations in tetrahedral (A) and octahedral [B] sites of the spinel. The hysteresis loops indicated that the saturation magnetization and coercivity increased with R-substitution and appeared to be greatly affected by the nature of R ions. The obtained results are interpreted based on the rearrangement of cations between the A-site and B-site.     

Crystallographic and low frequency conductivity studies of the spinel systems CuFe2O4 and Cu1?xZnxGa0.1Fe1.9O4; (0.0 ≤ x ≤ 0.5)

Spinel solid solutions of CuFe₂O₄ and Cu_1−xZn_xGa_0.1Fe_1.9O₄ with (0.0 ≤ x ≤ 0.5) are synthesized. Crystallographic phase transformation from tetragonal-to-cubic occurred at x = 0.2. The derived structural parameters manifest that Zn occupies the tetrahedral A-site while Cu and Ga occupy the octahedral B-site and Fe distributes among A- and B-sites. Electrical conductivity measurements of these materials as a function of temperature and frequency revealed semiconducting behavior except CuFe₂O₄ sample, which has a metallic behavior at low frequency and at high frequency, semiconductor-to-metallic transition occurred as temperature increases. The metallic behavior in this sample is attributed to cation-cation interactions at B-site while, the semiconductor behavior in Cu_1−xZn_xGa_0.1Fe_1.9O₄ compounds is due to the cation–anion–cation interactions at the same site in the spinel lattice. All compositions exhibit transition with change in the slope of conductivity versus temperature curve. This transition temperature (T_c) decreases linearly with increasing Zn content x. The relation of the universal exponent s with temperature gives evidence that over large polaron OLP and correlated barrier hopping CBH conduction mechanisms are presented in CuFe₂O₄ and Cu_1−xZn_xGa_0.1Fe_1.9O₄ compounds respectively.     

Crystallographic and Low Frequency Conductivity Studies of the Spinel Systems CuFe_2O_4 and Cu_（1-x）Zn_xGa_（0.1）Fe_（1.9）O_4

Spinel solid solutions of CuFe2O4 and Cu1-xZnxGa0.1Fe1.9O4 with (0.0≤x≤0.5) are synthesized. Crystallographic phase transformation from tetragonal-to-cubic occurred at x=0.2. The derived structural parameters manifest that Zn occupies the tetrahedral A-site while Cu and Ga occupy the octahedral B-site and Fe distributes among A- and B-sites. Electrical conductivity measurements of these materials as a function of temperature and frequency revealed semiconducting behavior except CuFe2O4 sample, which has a metallic behavior at low frequency and at high frequency, metallic -to- semiconductor transition occurred as temperature increases. The metallic behavior in this sample is attributed to cation-cation interactions at B-site while, the semiconductor behavior in Cu1-xZnxGa0.1Fe1.9O4 compounds is due to the cation- anion -cation interactions at the same site in the spinel lattice. All compositions exhibit transition with change in the slope of conductivity versus temperature curve. This transition temperature (Tc) decreases linearly with increasing Zn content x. The relation of the universal exponent s with temperature gives evidence that over large polaron OLP and correlated barrier hopping CBH conduction mechanisms are presented in CuFe2O4 and Cu1-xZnxGa0.1Fe1.9O4 compounds respectively.     

Structural and Magnetic Study of Zn-Substituted NiGa y Fe 2−y O 4 Ferrite

Single-phase spinel ferrite Ni _1?x Zn _x Ga _y Fe _2?y O ₄ with (0.0≤x≤0.5) and y=0.5 samples were synthesized using solid-state reaction technique. These ferrites were investigated using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mössbauer effect (ME) spectroscopy. XRD patterns confirmed the formation of single-phase cubic spinel ferrites for all samples. Lattice parameter was found to decrease with the introduction of Ga ³⁺ in NiFe ₂ O ₄, and then to increase with the increasing of Zn ²⁺ content x. ME measurements illustrated a strong dependence on the zinc concentration. The cation distribution calculated from the ME spectra at room temperature indicated that the Ga ³⁺ ion substituted iron in both octahedral B and tetrahedral A- sites. Zn ²⁺ ions firstly introduced in A- site, and for higher x, they distribute in both B- and A- sites. VSM measurements indicated that the change in the value of saturation magnetization can be explained using the cation distribution obtained from ME measurements. The coercivity values can be interpreted on the basis of magneto-crystalline anisotropy.     

Superparamagnetism in Zn Substituted Copper-gallate Ferrite

Solid solution of spinel ferrite Cu1-xZnxFe2-yGayO4 with (0.0≤x≤0.5 and y=0.1) are synthesized. XRD measurements confirm the presence of single-phase tetragonal structure with c/a>1 for CuFe2O4 and samples with (x=0.0 and 0.1). The tetragonal phase is attributed to the presence of the cooperative Jahn-Teller Cu ions in the octahedral B-site in the spinel lattice. Tetragonal-to-cubic transformation is occurred at the compositional parameter x≥0.2 and the lattice parameter a is found to decrease with increasing Zn content x. 57Fe M(o)ssbauer measurements at 293K for these compounds reveal superparamagnetic phase for samples with (0.0≤x≤0.2). In contrast, M(o)ssbauer spectra at 12K for these materials show well ordered spectra where, the cation distribution and the hyperfine parameters are determined.     

Synthesis and Characterization of Calcium-Substituted Mg-Co-Cr Ferrite Nanoparticles with a Crystallite Size Less Than 10 nm

Journal of Superconductivity and Novel Magnetism - Calcium-doped Mg-Co-Cr nanoferrites were synthesized using the chemical auto-combustion method. X-ray diffraction (XRD) data have excluded...     

Generation of excited electronic states at the nonmetal surface by the hydrogen atoms beam

The low energy excitation electronic states by the hydrogen atoms at the nonmetal surface are described using several possible mechanisms. The study results of the luminescence excited surface of the phosphor ZnS-Tm during interaction with H atoms are reported. Nonstationary with time the light intensity from ZnS-Tm is detected. This phenomenon interpreted on basis of the exchange-associative mechanism taking into account the acceleration of the surface recombination of hydrogen atoms in the adsorbed layer of the vibrationally excited hydrogen molecules. The rates of the absorption and recombination of hydrogen atoms and the desorption rate of the hydrogen molecules are defined. The possible mechanisms of excitation of the surface electronic states during interaction with the hydrogen low-energy atoms are discussed.     

A plant for studying radiation and thermal desorption of gases from inorganic materials

A high-vacuum plant and methods for studying thermal and radiation-stimulated desorption from solid-state materials are described. Radiation-stimulated desorption was studied using an electron gun with a 1- to 120-keV beam energy, featuring a new technology of power supply units. Partial pressure gages with a sensitivity of up to 10⁻¹³ Pa were used to record mass spectra of residual gases. Results of studying thermal- and radiation-stimulated yields of hydrogen from submicrocrystalline samples of a BT-6 alloy are presented to demonstrate the serviceability of the created procedures.