Preparation of nanometer CuFe2O4 by auto-combustion and its catalytic activity on the thermal decomposition of ammonium perchlorate

Nanometer copper ferrite was synthesized by auto-combustion method using cupric nitrate, ferric nitrate and malic acid as raw materials. The precursor and as-burnt sample were characterized by X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM) . Average particle size of sample is 26nm. The catalytic performance of nanometer CuFe₂O₄ on the thermal decomposition of ammonium perchlorate (AP) was investigated by DTA. The results show that the nanometer CuFe₂O₄ has high a catalytic activity, and the thermal decomposition temperature of AP shift 105 °C downward with the effect of nanometer copper ferrite. When the content of CuFe₂O₄ comes to 5%, the catalytic performance is the best.     

Structural and catalytic properties of Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

A series of zinc copper mixed ferrites having general formula Zn_1?x Cu _x Fe₂O₄ (x = 0.0, 0.25,0.50,0.75,1.0) have been synthesized by co-precipitation method. The average particle sizes of these ferrites as determined from XRD data using Scherer’s relation have been found to range from 10.45 to 18.39 nm. The samples have been characterized by XRD, Mössbauer spectroscopy, B.E.T.surface area and acidity measurements. These ferrites have been tested for their catalytic activity in alkylation of pyridine by methanol. The conversion of pyridine as well as yield to 3-methyl pyridine is found to be lowest in case of ZnFe₂O₄ which increases as the copper content is increased and is maximum for CuFe₂O₄. The results on the acidity measurements on these ferrites as well as structural properties support these results. CuFe₂O₄ is found to be highly selective for 3-methylpyridine.     

Influence of V2O5 additions on the permeability and power loss characteristics of Ni-Zn ferrites

Poly crystalline nickel-zinc ferrites with the chemical formula, Ni_0.65 Zn_0.35 Fe₂ O₄ + x V₂ O_5, where x values range from 0.0 to 1.5 wt.% in steps of 0.3 wt.%, have been prepared by conventional ceramic technique. The samples were sintered for 4 h in air at 1210 °C. The XRD analyses of the samples confirm single phase cubic spinel structures. Micrographs of the materials reveal that vanadium additions resulted in fine grain structures with small pores trapped inside the grains as the vanadium concentration increases. Complex permeability of these ferrites exhibit stable frequency responses up to 7 MHz beyond which the real part decreases sharply and the imaginary part increases to have a peak at the relaxation frequency. Power loss has been found to be quite low for these materials up to 3 MHz, thereafter it increases steeply due to large eddy current losses. The results are explained in terms of the compositional and microstructural modifications brought about by the vanadium additions.     

Synthesis of nanocrystalline xCuFe2O4-(1 − x)BiFeO3 magnetoelectric composite by chemical method

xCuFe₂O₄-(1 − x)BiFeO₃ spinel-perovskite nanocomposites with x = 0.1, 0.2, 0.3 and 0.4 were prepared using citrate precursor method. X-ray diffraction (XRD) analysis showed phase formation of xCuFe₂O₄-(1 − x)BiFeO₃ calcined at 500 °C. Transmission electron microscopy (TEM) shows formation of nanocrystallites of xCuFe₂O₄-(1 − x)BiFeO₃ with an average particle size of 40 nm. Variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Coercivity, saturation magnetization and squareness have been found to vary with concentration of ferrite phase and annealing temperature due to the increase in crystallite size. Squareness and coercivity increased with an increase in annealing temperature up to 500 °C and then decreased with a further increase in temperature to 600 °C. Magnetoelectric effect of the nanocomposites was found to be strongly depending on the magnetic bias and magnetic field frequency.     

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.     

Solid-state reactions in the system CaONd2O3Fe2O3Al2O3

Inherently cementitious ceramic compositions made by sintering show promise as host materials for the containment of radioactive wastes. The distribution of lanthanons in Ca-rich compositions has been explored using Nd as a model 4f element. Phase relations in the relevant portions of the CaONd₂O₃Fe₂O₃A$\text{l}$₂O₃ system show the coexistence of calcium aluminates and ferrites with Nd-melilites, perovskites, and K₂NiF₄-type phases.     

Synthesis and characterization of Bi2Fe4O9 powders

Bi₂Fe₄O₉ have been successfully prepared using ethylenediaminetetraacetic (EDTA) acid as a chelating agent and ethylene glycol as an esterification agent. Heating of a mixed solution of EDTA, ethylene glycol, and nitrates of iron and bismuth at 140 °C produced a transparent polymeric resin without any precipitation, which after pyrolysis at 250 °C was converted to a powder precursor for Bi₂Fe₄O₉. The precursors were heated at 400–800 °C in air to obtain Bi₂Fe₄O₉ powder and differential scanning calorimetry (DSC), thermogravimetric (TG), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) techniques were used to characterize the precursors and the derived oxide powders. XRD analysis showed that well-crystallized and single-phase Bi₂Fe₄O₉ with orthorhombic symmetry was obtained at 700 °C for 2 h and BiFeO₃ and Fe₂O₃/FeCO₃ were intermediate phases before the formation of Bi₂Fe₄O₉. Bi₂Fe₄O₉ powders show weak ferromagnetism at room temperature.     

Solvent-free preparation of copper ferrite microspheres composed of nanorods using a new coordination compound as precursor

This work presents a simple solvent-free route based on solid-state thermal decomposition approach to synthesize magnetic copper ferrite (CuFe₂O₄) microspheres and copper ferrite/metal oxide composites. For this purpose, [Cu(en)₃]₃[Fe(ox)₃]₂ complex (where en?=?ethylenediamine and ox?=?oxalate) was introduced as a new single-source precursor. Ferromagnetic property of the nanostructures was determined by alternating gradient force magnetometer. The effect of different ligands and temperatures on the morphology of the products was investigated. Solid-state thermal decomposition of the precursor at different temperatures in the range of 400–800?°C led to the fabrication of magnetic copper ferrites with various particle sizes. X-ray powder diffraction patterns and images of scanning electron microscopy showed formation of CuFe₂O₄/Fe₂O₃ microspheres with very smooth surfaces and CuFe₂O₄/CuO microspheres coated with nanorods by thermal decomposition of the precursor at 400 and 700?°C, respectively. The results confirmed that copper ferrite and CuFe₂O₄/CuO nanocomposites were suitable materials with appropriate performance in catalyst and photo-catalytic applications.     

Neodymium-doped copper ferrite: auto-combustion synthesis,characterization and photocatalytic properties

Neodymium doped copper ferrite nanoparticles were successfully synthesized by via a sol–gel auto combustion method with the aid of copper (II) nitrate, iron (III) nitrate, neodymium (III) nitrate and starch without adding external surfactant. Moreover, starch plays role as capping agent, reductant agent, and natural template in the synthesis CuFe_2?xNd_xO₄ nanoparticles. The as-synthesized CuFe_2?xNd_xO₄ nanoparticles were characterized by means of several techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis and UV–Vis diffuse reflectance spectroscopy. The magnetic properties of as-prepared CuFe_2?xNd_xO₄ nanoparticles were also investigated with vibrating sample magnetometer (VSM). To evaluate the photocatalyst properties of nanocrystalline CuFe_2?xNd_xO₄, the photocatalytic degradation of methyl orange (MO) under ultraviolet light irradiation was carried out.     

Effect of PbO-SiO2 and PbO-B2O3 flux systems on the crystalline and magnetic properties of Ni0.5Zn0.5Fe2O4 ferrite prepared from the mixed powders

Lead borate and lead silicate were added to lower the sintering temperature of a Ni_0.5Zn_0.5Fe₂O₄ ferrite prepared from the blend of two types of powders and to homogenize the grain size. 5PbO·SiO₂ and 5PbO·B₂O₃ flux systems were added to lower the sintering temperature and diminish the magnetic loss at high frequencies. The ferrites were studied by bulk density, scanning electron microscopy and impedance analysis. It was found that the addition of PbO markedly accelerated the grain growth, while SiO₂ and B₂O₃ were found to be effective to obstruct the movement of grain boundaries and to minimize the grain size. Doping with PbO in the mixed powders appropriately increased the densification and initial permeability. The ferrite doped with 1% of 5PbO·SiO₂ possessed the lowest loss tangent (tgδ) in the range of 5 M-40 MHz and the highest threshold frequency.     

Synthesis and photoluminescence properties of SrLu2O4:Eu superfine phosphor

Superfine powder SrLu₂O₄:Eu³⁺ was synthesized with a precursor prepared by an EDTA - sol-gel method at relatively low temperature using metal nitrate and EDTA as starting materials. The heat decomposition mechanism of the precursor, formation process of SrLu₂O₄:Eu³⁺and the properties of the particles were investigated by thermo-gravimetric (TG) - differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) analyses. The results show that pure SrLu₂O₄:Eu³⁺ superfine powder has been produced after the precursor was calcinated at 900 °C for 2 h and has an elliptical shape and an average diameter of 80-100 nm. Upon excitation with 250 nm light, all the SrLu₂O₄:Eu³⁺ powders show red and orange emissions due to the 4f-4f transitions of Eu³⁺ ions. The highest photoluminescence intensity at 610 nm was found at a content of about 6 mol% Eu³⁺. Splitting of the ⁵D₀-⁷F₁ emission transition revealed that the Eu³⁺ ions occupied two nonequivalent sites in the crystallite by substituting Lu³⁺ ions.     

Synthesis and electrochemical properties of nanostructured LiMn2O4 for lithium-ion batteries

Spinel LiMn₂O₄ crystal with the grain sizes of about 15 nm is firstly synthesized by hydrothermal route at 180 °C using MnO₂ as a precursor. The LiMn₂O₄ powders synthesized by hydrothermal technique and sol-gel reaction were investigated by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The LiMn₂O₄ samples were used as cathode materials for lithium-ion battery, whose electrochemical properties were investigated. The results show that the sample obtained by hydrothermal route has higher capacity than that prepared by sol-gel method.     

Preparation and characterization of spinel-type MeFe2O4 (Me = Cu,Cd, Ni and Zn) for catalyst applications

Four kinds of spinel ferrites, MeFe₂O₄ (Me = Cu, Ni, Zn and Cd), were prepared by so called “selfcombustion method” using nitrates as precursors. The morphological and structural characterization of the ferrite powders have been performed with various techniques: X-ray diffraction (XRD), to determine the phase composition, SEM observations to evaluate nanostructure characteristics, EDAX spectroscopy to evaluate the chemical composition and BET analysis to determine the specific surface area. The ferrite powders have been tested catalytically in combustion reaction of three diluted gases: acetone/air, ethanol/air and methanol/air. The results revealed a pronounced decrease in the combustion temperature when Cu- and Ni-ferrites are used as catalysts. A probable cause was ascribed to multiple valences of Cu and Ni ions which favor a rapid increase in the oxygen ion species adsorbed on ferrite surface.     

Low temperature synthesis of nanocrystalline Li4Mn5O12 by a hydrothermal method

A mild hydrothermal method using Li-birnessite (Li_xMnO₂·nH₂O) ultrafine fiber as the precursor has been adopted to prepare Li₄Mn₅O₁₂, which is of interest as an electrode material for 3 V rechargeable lithium ion batteries. X-ray diffraction data reveal that the obtained powders have a pure spinel structure with a lattice constant of 8.135 Å. The scanning electron microscopy image of the obtained powders shows the particles are cubic-shaped whose average size is about 40-50 nm. The results from inductively coupled plasma-atomic emission spectroscope and wet chemical analysis indicate that a Li/Mn ratio of 0.796, and an average valence of 3.96 of Mn ion have been achieved in the as-prepared products. The thermogravimetric and differential thermal analysis data also agree with the previous reports on Li₄Mn₅O₁₂, suggesting that near stoichiometry of Li₄Mn₅O₁₂ has been synthesized by this procedure at the rather low temperature 110°C.     

Synthese de quelques ferrites par reaction de double decomposition entre le ferrite de lithium (LiFeO2) et un sel fondu

In this paper are specified the conditions of formation of pure ferrites by the double decomposition reaction between the lithium ferrite and divalent metal double salts such as chlorides. 2 LifeO₂ + K₂MCl₄ → MFe₂O₄ + 2 LiCl + 2 KCl (M=Co,Ni,Mn,Zn,Mg) These reactions can be achieved at 600°C with an excess of molten double salt in absence of oxygen and water vapor. Spinel mixed iron oxides are obtained as fine spherical particles with a narrow granulometric repartition (0,1 to 0,2 μ). The formation of pure cupric ferrite CuFe₂ O₄ is not possible because the decomposition of cupric salt in our reaction conditions cannot be avoided.     

Synthesis of nanocrystalline MgAl2O4 spinel powders by a novel chemical method

A novel chemical method for the preparation of nanocrystalline MgAl₂O₄ spinel powders has been developed in this paper. The mixed magnesium-aluminum hydroxide precipitates were initially formed in a three-dimensional space network microarea. After being calcined at above 700 °C, the nanocrystalline MgAl₂O₄ spinel powders were obtained. The precursor and as-calcined powders were characterized using TGA-DTA, XRD and TEM. The MgAl₂O₄ spinel powders calcined at 850 °C for 2 h are of narrow distribution, little agglomeration and small particle size of ∼ 24 nm. The reason for the synthesis of high-quality powders was explained.     

Influence of 150 MeV Ni swift heavy ion irradiation on CuFe2O4 thin films prepared by radio frequency magnetron sputtering: Modification on structure and surface morphology

The bulk copper ferrite nanomaterials are synthesized by co-precipitation technique. The vibrating sample magnetometer measurement for bulk CuFe₂O₄ reveals its unsaturated superparamagnetic behavior. The crystallites of the synthesized nanomaterial are in cubic form having an average size of ~ 100 Å and are used as target to prepare thin films of various thicknesses (600, 900 and 1100 nm) by radio frequency magnetron sputtering technique. X-ray peaks arise only when films are annealed at 1200 °C and also they are found to be in tetragonal structure. The magnetic characteristics of 900 nm unirradiated CuFe₂O₄ thin film exhibit superparamagnetic behavior and have an unsaturated magnetic moment at high field. Magnetic force microscopy images of unirradiated CuFe₂O₄ thin films confirm the soft nature of the magnetic materials. The 150 MeV Ni¹¹⁺ swift heavy ion irradiation on these thin films at the fluence of 1 × 10¹⁴ ions/cm² modifies the polycrystalline nature due to electron-phonon coupling. Atomic force microscopy image shows that the swift heavy ion irradiation induces agglomeration of particles in 600 and 900 nm thin films and increases rms surface roughness from 33.43 to 39.65 and 69.7 to 102.46 nm respectively. However, in 1100 nm film, holes are created and channel-like structures are observed along with a decrease in the rms surface roughness from 75.12 to 24.46 nm. Magnetic force microscopy images of 900 nm irradiated thin film explain the formation of domains on irradiation and are also supported by the ferromagnetic hysteresis observed using vibrating sample magnetometer.     

Multiferroic properties of Pb2Fe2O5 ceramics

Pb₂Fe₂O₅ (PFO) powders in monoclinic structure have been synthesized using lead acetate in glycerin and ferric acetylacetonate as the precursor. The powders were pressed into pellets, which were sintered into ceramics at 800 °C for 1 h. The morphology and structure have been determined by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). Polarization was observed in Pb₂Fe₂O₅ ceramics at room temperature, exhibiting a clear ferroelectric hysteresis loop. The remanent polarization of Pb₂Fe₂O₅ ceramic is estimated to be Pr ∼ 0.22 μC/cm². The origin of the polarization may be attributed to the off-centers of shifted Pb²⁺ ions as well as the FeO₆ octahedra in the perovskite-based structure of Pb₂Fe₂O₅. Magnetic hysteresis loop was also observed at room temperature. The Pb₂Fe₂O₅ ceramic shows coexistence of ferroelectricity and ferromagnetism. It provides a new field of research for complex oxides with multiferroic properties.     

Comparison of microwave-induced combustion and solid-state reaction method for synthesis of LiMn2− x Co x O4 powders and their electrochemical properties

Spinel LiMn_{2 − x}Co_xO₄ (0.00 ≦ x ≦ 0.20) powders with small and uniform particle size were successfully synthesized by microwave-induced combustion using lithium nitrate, manganese nitrate, cobalt nitrate, and urea as the starting materials. The LiMn_{2 − x}Co_xO₄ powders synthesized by microwave-induced combustion were investigated by X-ray diffractometer (XRD), thermogravimeter analyzer (TG), and scanning electron microscopy (SEM). The LiMn_{2 − x}Co_xO₄ samples were used as cathode materials in lithium-ion batteries, whose discharge capacity and electrochemical characteristics such as the cycling performance were also investigated. The results revealed that the LiMn_{2 − x}Co_xO₄ cell synthesized by microwave-induced combustion provided a high initial capacity and excellent reversibility compared to the material prepared by solid-state reaction method.     

Solvent-free synthesis of hexagonal barium ferrite (BaFe12O19) particles

M-type barium ferrite (BaFe₁₂O₁₉) particles, from a mixture of barium nitrate, ferric nitrate, cetyltrimethylammonium bromide (CTAB), and ammonium carbonate, have been successfully prepared through simple grinding and calcination in the absence of any solvent. The products are characterized by X-ray diffraction, scanning electron microscope, and vibrating sample magnetometer, whose results indicate that they have well crystalline phase of BaFe₁₂O₁₉, typically hexagonal platelet-like structure, large saturation magnetization, even submicrometer particle size under the optimum condition. Meanwhile, the effects of Fe/Ba ratio, CTAB, and ammonium carbonate are also investigated. It has been found that the proper Fe/Ba ratio could suppress the intermediate phase such as α-Fe₂O₃ and BaFe₂O₄, CTAB could promote the crystallinity of BaFe₁₂O₁₉ and produce hexagonal crystal structure, and ammonium carbonate was the key for forming BaFe₁₂O₁₉ phase. This facile method may be helpful for the preparation of other multicomponent functional materials.