Novel solid solution precursor method for the preparation of ultrafine Ni-Zn ferrites

Ultrafine Ni-Zn ferrites, Ni _x Zn_1-x Fe₂0₄, have been prepared by the thermal decomposition/combustion of novel solid solution precursors of the type, (N₂H₅)₃N_1-x Zn_1-x Fe₂(N₂H₃C00)₉ · 3H₂0 wherex = 0.2 to 0.8. The novelty of the precursors being their low temperature, exothermic, gas producing self-sustained decomposition. Fine particle nature of the ferrites has been indicated by X-ray powder diffraction, transmission electron microscopy and surface area measurements. Fine particle Ni-Zn ferrites sinter at 1000° C, 24 h to achieve almost 99% theoretical density.     

Chemical vapour deposition of epitaxial Ni-Zn ferrite films by thermal decomposition of acetylacetonato complexes

Epitaxial (Ni, Zn)Fe₂O₄ films were prepared on (100) MgO single crystal substrate by lowpressure chemical vapour deposition using a thermal decomposition of acetylacetonatocomplexes, Ni(acac)₂, Zn(acac)₂ and Fe(acac)₃. These complexes were evaporated at 157, 79 and 146° C, respectively, and transported with nitrogen carrier gas (flow rate 100 ml min⁻¹) to the deposition furnace. Polycrystalline and epitaxial films were grown at 500 to 600 and 600 to 650° C, respectively, under a pressure of 12 torr. The epitaxial film of Ni_1−xZn_xFe₂O₄ (x⋍0.4) treated at 600° C for 60 min, showed the saturation magnetization of 67 e.m.u. g⁻¹ and the coercive force of 20 to 30 Oe.     

Nanocrystalline spinel Ni0.6Zn0.4Fe2O4: A novel material for H2S sensing

Nanocrystalline powders of Ni_1?xZn_xFe₂O₄ (0 ≤ x ≤ 0.5) mixed ferrites, with cubic spinel structure and average crystallite size ranging from 28 to 42 nm, were synthesized by the ethylene glycol mediated citrate sol–gel method. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). The response of prepared Ni_1?xZn_xFe₂O₄ mixed ferrites to different reducing gases (liquefied petroleum gas, hydrogen sulfide, ethanol gas and ammonia) was investigated. The sensor response largely depends on the composition, temperature and the test gas species. The Zn content has a significant influence on the gas-sensing properties of Ni_1?xZn_xFe₂O₄. Especially, Ni_0.6Zn_0.4Fe₂O₄ composition exhibited high response with better selectivity to 50 ppm H₂S gas at 225 °C. Incorporation of palladium (Pd) further improved the response, selectivity and response time of Ni_0.6Zn_0.4Fe₂O₄ to H₂S with the shift in the operating temperature towards lower value by 50 °C. The enhanced H₂S sensing properties can mainly be attributed to the selectivity to oxidation of H₂S and noble metal additive sensitization. Furthermore, the sensor exhibited a fast response and a good recovery.     

Hydrothermal formation of Ni-Zn ferrite from heavy metal co-precipitates

The hydrothermal synthesis of Ni-Zn ferrite from simulated wastewater containing Ni²⁺ and Zn²⁺ ions has been studied. The influence of co-precipitation order, the existence of Na⁺ in suspension, the hydrothermal reaction time and temperature on the composition, morphology and saturation magnetization (_s) of the hydrothermal products is reported. Adding the simulated wastewater to the NaOH solution can prevent the formation of -Fe₂O₃ in the Ni-Zn ferrite. Increasing the hydrothermal reaction time improved the magnetization of the Ni-Zn ferrite, while the influence of temperature, stirring intensity and Na⁺ in suspension on the hydrothermal formation of ferrite were not obvious. Thermodynamic calculation indicated that under hydrothermal conditions (180–240°C), the order of chemical stability is as follows: NiFe₂O₄ > Fe₂O₃ > Na₂Fe₂O₄. The high Gibbs formation energy of Na₂Fe₂O₄ prevented the incorporation of Na⁺ into the ferrite lattice.     

Cation distribution in nanocrystalline Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel ferrites

We have studied the cation distribution over the tetrahedral and octahedral sites in the spinel structure of nanocrystalline Ni _x Zn_{1 ? x} Fe₂O₄ ferrites prepared by spray pyrolysis. ⁵⁷Fe Mössbauer spectroscopy data for the ferrites demonstrate that, depending on the composition of the materials, the tetrahedral site may accommodate only Fe³⁺ (inverse spinel, x ≥ 0.4) or both Fe³⁺ and Zn²⁺ cations (mixed spinel, x = 0 and 0.2), which accounts for the fact that the composition dependence of the unit-cell parameter for the ferrites deviates from Vegard’s law.     

Phase Composition of the Products of Fe Oxidation in Fe + C + NaCl + H2O + O2 Exothermic Mixtures

Using thermodynamic analysis of the Fe–C–NaCl–H₂O–O₂ system and experimental studies (x-ray diffraction and Mössbauer spectroscopy) of exothermic mixtures containing Fe metal, activated carbon, water, and NaCl, we identified the state of Fe and determined the phase composition of the reaction products at different stages of oxidation with atmospheric oxygen. The calculation and experimental results are in reasonable agreement. Under the conditions of restricted access for air, the main oxidation product is magnetite, Fe₃O₄. Free access for air leads to the formation of hydrous ferric oxide, Fe₂O₃ · nH₂O. The most stable phase under the conditions of interest is goethite, Fe₂O₃ · H₂O (-FeOOH). Storage of incompletely oxidized samples away from air for 7–14 days leads to partial reduction of iron(III) oxide phases to Fe₃O₄ and -Fe.     

Soft magnetic and high-frequency properties of Ni-Zn ferrite film with FeMn underlayer

Ni_0.45Zn_0.55Fe₂O₄ (40 nm) single-layer and Fe₅₀Mn₅₀ (25 nm)/Ni_0.45Zn_0.55Fe₂O₄ (40 nm) bilayer films were prepared on Si(111) substrates by radio frequency magnetron sputtering at room temperature, and the influence of FeMn underlayer on the microstructure and magnetic property of Ni-Zn ferrite film has been investigated. It was found that the introduction of Fe₅₀Mn₅₀ underlayer resulted in a decrease from 7.1 to 3.1 kA/m in coercivity and increase from 0.22 to 0.60 in residual magnetization ratio of the ferrite film. The complex permeability μ = μ′ − iμ″ values of the films were measured at a frequency of up to 5 GHz. An obvious resonance peak at about 1.65 GHz of the bilayer film appeared in the permeability spectrum. The reason has been researched preliminarily and was ascribed to the change of the film's microstructure with FeMn underlayer.     

Low-temperature formation mechanism of double oxides Fe x Zr(Ti)1−0.75x O2−δ prepared from alkoxides and acetylacetonates

As a result of titanium and zirconium alcoholates hydrolysis in the presence of dissolved Fe(acac)₃, amorphous iron-containing gels have been synthesized. Their heat treatment has led to polycrystalline double oxides Fe _x Zr_1–0.75x O_2– (C) and Fe _x Ti_1–0.75x O_2– (T) formation. It has been shown that oxides (C) and (T) are likely to be solid solutions with 0.01<x<0.17 and 0.01<x<0.14, respectively. On the basis of X-ray diffraction and extended X-ray absorption fine structure data, iron-zirconium and iron-titanium crystallite models for gels and oxides have been proposed. It has been found that the crystallization process does not lead to a significant change in interatomic distances typical for local structures detected in gels.     

Structure and magnetic properties of Ni0.11ZnxCo0.03Fe2.86-xO4 ferrite films deposited on Ag-coated glass substrates by wet chemical method

Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ spinel ferrite films with x = 0.00, 0.23, 0.34, 0.43 and 0.51 were prepared on Ag-coated glass substrates from nitrate and dimethylamine borane solution at 80 °C. The Ni_0.11Zn_xCo_0.03Fe_2.86-xO₄ ferrite films are singe-phased spinel ferrite. With the Zn content x increasing from 0 to 0.51, the lattice constant of the ferrite films increases from 0.8383 to 0.8425 nm. The Ni_0.11Zn_0.51Co_0.03Fe_2.35O₄ film is about 500 nm thick and composed of uniform equiaxed granules of about 40–50 nm. The Raman spectrum analysis indicates that the Zn²⁺ ions occupy the A sites. Saturation magnetization increases with x increasing from 0 to 0.35, reaches a maximum value of 460 kA/m at x = 0.35, and then decreases with further increase of x. Coercivity decreases monotonically from 12.3 to 1.7 kA/m with x increasing from 0 to 0.51. The change in magnetic properties may be explained by the decrease of A–B interactions and the anisotropy constant due to the incorporation of non-magnetic Zn²⁺ ions.     

The synthesis and thermal behaviour of zinc diphosphates

Zinc diphosphates (Zn₂P₂O₇ · 5H₂O, Zn₂P₂O₇ · 3H₂O, 5K_1.4Zn_1.3P₂O₇ · 16H₂O, and 5K_0.8Zn_1.6P₂O₇ · 9H₂O) were made by the wet process. The composition of the products was dependent on the conditions (concentration, pH, and dropping rate of the solution) of the process. When the products were heated, decomposition of the diphosphates to orthophosphate took place below about 150 ·C. Polymerization of the phosphates to phosphates with longer chains was observed in the temperature range 150 to 400 ° C. The amorphous phosphates thermally produced by heating diphosphates other than 5K_1.4Zn_1.3P₂O₇ · 16H₂O, showed reorganization to diphosphate above 400 ° C according to the reaction M₂O₃PO[P(O₂M)O] _n PO₃M₂ +nM₃PO₄(n + 1)M₄P₂O₇ where M represents K and/or 1/2Zn.     

Growth and magnetic properties of ultrathin Ni1 + xFe2 − xO4 films for spin filter junctions

We investigated the spin filter effect in tunnel junctions with a Ni_1 + xFe_2 − xO₄ ferrimagnetic tunnel barrier. For higher T_c above room temperature, Ni_1 + xFe_2 − xO₄ film should be thicker than 4.0 nm and grown above 400 °C. The spin filter junctions (SFJs) of Fe₃O₄(001)/Ni_1 + xFe_2 − xO₄(001)/Al₂O₃/Fe/Au grown on MgO(001) substrates exhibited an inverse magnetoresistance effect at room temperature, which is consistent with the band calculation of NiFe₂O₄.     

Magnetic and electrical properties of hot-pressed Ni-Zn-Li ferrites

The magnetic properties of Ni-Zn ferrites have been upgraded by preparing hot-pressed Ni_0.4Zn_0.6–2xLi_xFe_2+xO₄ ferrites wherein 2xZn²⁺ ions have been substituted byxLi¹⁺ andxFe³⁺ ions. This results in an increase of saturation magnetization, Curie temperature and dielectric constant, whereas resistivity and initial permeability are reduced. The values of saturation magnetization, Curie temperature and dielectric constant are improved due to hot pressing in which grain growth and densification are controlled simultaneously. The variations of saturation magnetization and Curie temperature can be explained by the preferential site occupancy of Li¹⁺ and Ni²⁺ ions at the tetrahedral site, sublattice magnetization with canted spin structure, and magnetic exchange interactions. The inferences drawn from the bulk magnetic properties of these ferrites conform with the conclusions drawn from variations of internal magnetic field, obtained from Mössbauer studies of these samples. The decrease in d.c. resistivity due to substitution of Li¹⁺ ions is attributed to increased hopping due to formation of Fe²⁺ and Ni³⁺ ions.     

Electrical properties of Ni–Mn–Co–(Fe) oxide thick-film NTC thermistors prepared by screen printing

Ni–Mn–Co–(Fe) oxide thick films were coated on an alumina substrate by a screen-printing technique. The electrical properties of the thick films, as a function of composition and sintering temperature, were investigated. All the thick-film negative temperature coefficient (NTC) thermistors prepared showed a linear relationship between log resistivity and the reciprocal of the absolute temperature, indicative of NTC characteristics. As the amount of Mn₃O₄ in (Ni_2–x Mn _x Co_1.0)O₄ (0.6x1.8) thermistors increased, the resistivity and the coefficient of temperature sensitivity decreased to a minimum value and then increased again. Also, at a given Ni–Mn oxide content, the resistivity and the coefficient of temperature sensitivity for (Ni_1.0Mn_1.0Co_1–x Fe _x )O₄ (0.25x1.0) and (Ni_0.75Mn_1.25Co_1–x Fe _x )O₄ (0.25x0.75) thermistors increased with increasing Fe₂O₃ content. The influence of composition and sintering temperature on the electrical properties of the thermistors is discussed.     

Influence of Oxygen Modification and Alloying on the Charge–Discharge Characteristics of Metal-Hydride Electrodes Based on Ti2Ni

An improvement of discharge capacity of metal-hydride electrodes based on hydrides of Ti_4 – x Zr _x Ni₂O _y alloys (0.2 x 0.6; 0.2 y 1.0) was shown during simultaneous partial Ti Zr substitution and oxygen modification. The maximal value of C _p (311 A · h · kg^–1) was experimentally found for a metal-hydride electrode based on Ti_3.6Zr_0.4Ni₂O_0.6H_5.2. High cyclic stability was shown for the oxygen-containing Ti_3.6Zr_0.2V_0.2Ni₂O_0.3 and Ti_3.8V_0.2Ni₂O_0.3 alloys alloyed with vanadium.     

Characterization of crystallization in Metglas 2826 MB alloy

The crystallization behaviour of the Metglas 2826 MB alloy (Fe₄₀Ni₃₈Mo₄B₁₈) has been studied using resistance measurements and X-ray diffraction techniques. Three annealing sequences were used to follow the process. Samples were annealed isothermally (a) at 780° C in a vacuum of 2×10^–5 torr for times in the range 1 sec to 4 h, (b) for 2 h in an argon atmosphere at temperatures where the resistance curve indicated phase changes to occur, and (c) for 300 h in 100 torr of helium at 400, 600, 700 and 850° C. From these annealing sequences it was found that the alloy did not crystallize below 410° C and followed a crystallization process of: amorphous Fe₄₀Ni₃₈Mo₄B₁₈ Fe _x Ni_23–x B₆ (cubic)+glassy matrix Fe _x Ni_23–x B₆+(Fe, Ni) (FCC) (Fe, Ni)₃B(bct). This series of transformations was followed for Sequences (a) and (c) above, but was slightly different for Sequence (b). An orthorhombic (Fe, Ni)₃ B phase was found in the samples annealed in a vacuum of 2×10^–5 torr.Trademark of Allied Chemical Co.     

Band gap determination of Ni-Zn ferrites

Nanocomposites of Ni-Zn with copolymer matrix of aniline and formaldehyde in presence of varying concentrations of zinc ions have been studied at room temperature and normal pressure. The energy band gap of these materials are determined by reflection spectra in the wavelength range 400–850 nm by spectrophotometer at room temperature. From the analysis of reflection spectra, nanocomposites of copolymer of aniline and formaldehyde with Ni_1-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 10) have been found to have direct band gaps ranging from 1.50–1.66 eV.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.     

Electrical conduction in γ-irradiated and unirradiated Fe3O4, CdFe2O4 and Co x ZN1−x Fe2O4 (0 ⩽x ⩽ 1) ferrites

The electrical conductivity of -irradiated and unirradiated finely divided ferrites of composition Fe₃O₄, CdFe₂O₄ and Co _x Fn_1–x Fe₂O₄(0 x 1) was studied in a nitrogen atmosphere as a function of temperature. Fe₃O₄, ZnFe₂O₄ and CdFe₂O₄ showed n-type conduction, whereas CoFe₂O₄ showed p-type conduction. For Co _x Zn_1-x Fe₂O₄ it was found that the type of conduction varies with the composition of ferrites. The electrical conduction in Fe₃O₄, and Co _x Zn_1–x Fe₂O₄(0 x 1) was explained by a hopping mechanism, whereas the conduction in ZnFe₂O₄ and in CdFe₂O₄ is interpreted on the basis of the transfer of charge carriers through cation vacancies present on octahedral sites. The effect of -irradiation on the conductivity, activation energy, charge carriers and the conduction mechanism is discussed.     

Combustion synthesis, sintering and magnetical properties of nanocristalline Ni-Zn ferrites doped with samarium

An investigation was made of combustion synthesis to uniformly incorporate small amounts of samarium additive into nanocrystalline Ni_0.5Zn_0.5Fe_{2 – x} Sm _x O₄ (0.0 x 0.1) nanopowders (26–20 nm particle size). The effect of the addition of the rare-earth ion samarium on the microstructure, relative density and magnetic properties of the Ni-Zn ferrite obtained by combustion reaction was studied. The samples were uniaxially compacted by dry pressing, sintered at 1200°C/2 h, and characterized by bulk and apparent density, XRD, SEM and magnetic properties. The nanopowder samples without additive displayed an average grain size of 2.87 m, while the addition of 0.05; 0.075 and 0.1 wt% Sm was found to inhibit grain growth, decreasing the average grain size to 0.77; 0.68 and 0.62 m, respectively. The relative density was found to increase with the addition of samarium (>98.00% of the theoretical density). The samples without additive showed higher hysteresis parameter values.     

Substitution Effects on Rare-Earth Ions-Doped Nickel-Zinc Ferrite Nanoparticles

Rare-earth ions (RE³⁺)-doped Ni-Zn ferrite nanoparticles with a structural formula of Ni_0.5Zn_0.5Fe_1.8RE_0.2O₄ (RE³⁺ = Nd, Ce, La and Pr) were synthesized at room temperature by a sol-gel auto-combustion method. The structural and magnetic properties of Ni-Zn ferrite samples were carried out by XRD, vibrating sample magnetometer (VSM), field emission scanning electron microscopy (FE-SEM) and FT-IR spectroscopy. XRD pattern of Ni-Zn ferrite revealed that all the diffraction planes are in agreement with cubic spinel phase and the addition of Fe₂O₃ phase was also observed. In the case of RE ions-doped Ni-Zn ferrite in addition to the Fe₂O₃ phase, very low intensity peaks corresponding to some secondary phase are also present. The average crystallite sizes were found to be from 42 to 56 nm using the Scherer formula. The lattice constant (a) values are gradually decreased from 8.378 to 8.349 Å with different substitutions of RE³⁺ ions in the Ni-Zn ferrite samples. VSM analysis revealed that saturation magnetization values are decreased and coercivity values are increased with substitution of different RE³⁺ ions. FE-SEM images exhibits that particles are spherical in shape. FT-IR interpretation revealed that two main metal oxygen bands (564 and 411 cm^?1) are observed in all the substituted Ni-Zn ferrite samples.