Cathodic electrosynthesis of CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/CuO composite nanostructures for high performance supercapacitor applications

In this work, CuFe₂O₄/CuO nanocomposites have been synthesized by galvanostatic cathodic electrodeposition. The obtained nanocomposites were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Fourier Transform Infrared, and Brunauer–Emmett–Teller surface area analysis. The electrochemical properties of CuFe₂O₄/CuO nanocomposites were evaluated by cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy in 1.0 M KOH. The CuFe₂O₄/CuO nanocomposites have shown the high specific capacitance of 322.49 F g^?1 at the scan rate of 1 mV s^?1. After 5000 cycles, 92% of this specific capacitance was retained. Although the prepared nanocomposite has shown a mediocre specific capacitance compared to other metal oxide-based materials, the low cost of the starting materials and the ease of preparation make this nanocomposite a good candidate for supercapacitor applications.     

Oxygen storage and release behavior of delafossite-type CuFe1−x Al x O2

Delafossite-type solid solution, CuFe_1?x Al _x O₂, was synthesized and its oxygen storage capacity (OSC) was investigated under oxidation/reduction cycle using a pulse injection method. CuFe_1?x Al _x O₂ was synthesized by heating at 1100–1150 °C in N₂ flow. OSC values for x = 0.1 and 0.3 were larger than that for x = 0 above 500 °C, indicating that substitution of Fe³⁺ by Al³⁺ improved OSC. For x = 0.5–1.0, temperature at which OSC increased steeply shifted upward. Results of X-ray diffraction (XRD) after the thermogravimetry and differential thermal analysis (TG–DTA) measurement in air for CuFe_1?x Al _x O₂ (x = 0–0.7) indicated that oxidative decomposition of delafossite phases to CuO and spinel-type phase occurred. In addition, Cu reduction temperature estimated by the temperature programmed reduction using H₂ (H₂-TPR) shifted to higher temperature with increasing Al content. The XRD results of the samples after H₂ and O₂/He pulse injection suggested that the oxygen storage/release behavior was caused by reversible oxidation/reduction process between CuFe_1?x Al _x O₂ delafossite and (Fe_1?x Al _x )₃O₄ spinel phase +Cu.     

Copper and iron based thin film nanocomposites prepared by radio-frequency sputtering. Part II: elaboration and characterization of oxide/oxide thin film nanocomposites using controlled ex-situ oxidation process

CuO/CuFe₂O₄ thin films were obtained on glass substrate by ex situ oxidation in air at 450 °C for 12 h from various starting metal/oxide nanocomposites by radio-frequency sputtering technique. The structure and microstructure of the films were examined using grazing incidence X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopies, X-ray photoelectron spectroscopy, and electron probe microanalysis. These studies reveal that a self-organized bi-layered microstructure with CuO (surface layer) and CuFe₂O₄ (heart layer) was systematically obtained. Due to the porosity of the upper layer formed during annealing, an increase in total thickness of the film was observed and is directly correlated to the oxidation of the metallic copper content initially present in the as-deposited sample. A self-organization in two stacked layers CuO/CuFe₂O₄ with various void fractions ranging from 0 to 41 % can be obtained by controlling the as-deposited elaboration step described in the part I of this paper. The highest porosities were observed for films deposited at low argon pressure and low target-to-substrate distance. Due to their specific self-organization in p- and n-type layers associated with their high porosity, such structured films exhibited the best electrical sensitivity to CO₂ gas sensing. The obtained results demonstrated the importance of microstructure control to improve the response of sensing layers.     

Controllable preparation of large-area arrays of Al-substituted CoCuNi ferrite rods with improvement of saturation magnetization and initial permeability

Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ (x = 0, 0.07, 0.14, and 0.21) rods of large-area arrays are synthesized by a solvothermal method, followed by calcination in air. The samples are characterized by powder X-ray diffraction, FT-IR spectra, scanning electron microscope, and vibrating sample magnetometer. The effect of diamagnetic Al³⁺ ion substitution and calcination temperature on the structure, morphology, and magnetic properties of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ has been investigated. The results indicate that high-crystallized cubic Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ rods of large-area arrays are obtained when the precursors are calcined at 750 °C in air for 3 h. The crystallite size of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ increases with the increase in Al³⁺ content, attributed to the decrease in lattice strain in Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ with the increase in Al³⁺ content. The lattice parameters of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄ slightly increase with the increase in Al³⁺ content. This is due to the transformation from cubic NiFe₂O₄ phase to cubic CoFe₂O₄ phase after doping Al³⁺ ion. Al³⁺ substitution can improve the magnetic properties of Co_0.5Cu_0.3Ni_0.2Al _x Fe_2?x O₄. Co_0.5Cu_0.3Ni_0.2Al_0.14Fe_1.86O₄, calcined at 950 °C, has the highest specific saturation magnetization (86.36 ± 2.25 emu/g) and magnetic moment (3.586 ± 0.093 μ _B ). Co_0.5Cu_0.3Ni_0.2Al_0.21Fe_1.79O₄, calcined at 950 °C, has the highest initial permeability (17.216 ± 0.448). The results are explained by Neel’s two sublattices.     

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.     

Structural and magnetic properties of spinel (Co,Cu)Fe2O4 ferrites prepared via a hydrothermal and sintering process

Spinel Co–Cu ferrites with the nominal composition Co_1?x Cu _x Fe₂O₄ ferrites (x = 0.0–0.4 with steps of 0.1) were prepared by a hydrothermal and sintering process, and the structural and magnetic properties of as-synthesized and sintered powder specimens were compared by using X-ray diffractometry, scanning electron microscopy, energy dispersive spectrometry and vibrating sample magnetometer analyses. It is found that all the as-synthesized and sintered specimens are single phase, and only suitable amount of Cu²⁺ substitution (x ≤ 0.3) is favorable for the growth of grains at high sintering temperature. In addition, with the increase of x, the saturation magnetization of both the as-synthesized and sintered powders decreases continuously, while the coercivity exhibits a first increasing but then decreasing tendency.     

Synthesis of magnetic Cu/CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanocomposite as a highly efficient Fenton-like catalyst for methylene blue degradation

A magnetic Cu/CuFe₂O₄ nanocomposite was synthesized by a facile one-pot solvothermal method and characterized as an excellent Fenton-like catalyst for methylene blue (MB) degradation. The content of zero-valent copper (Cu⁰) in Cu/CuFe₂O₄ composite could be simply controlled by changing the dosage of sodium acetate in the synthetic process, and the Fenton-like catalytic performance of Cu/CuFe₂O₄ composite enhanced with increasing the Cu⁰ content. In the presence of H₂O₂ (15 mM), the as-synthesized 3-Cu/CuFe₂O₄ nanocomposite could remove 99% of MB (50 mg/L) after only 4 min at pH 2.50, greatly higher than that of pure CuFe₂O₄ and Cu⁰ under the same condition. The enhancement activity of Cu/CuFe₂O₄ nanocomposite was due to the synergistic effect between Cu⁰ and CuFe₂O₄. The radical capture experiments and coumarin fluorescent probe technique confirmed that MB was degraded mainly by the attack of OH^· radicals in Cu/CuFe₂O₄–H₂O₂ system.     

Effect of synthesis conditions on the preparation of BiFeO<Subscript>3</Subscript> nanopowders using two different methods

Bismuth orthoferrite (BiFeO₃) nanoparticles have been synthesized via the co-precipitation and the oxalate precursor methods. Effects of Bi source, annealing temperature, Bi/Fe molar ratio, oxalic acid ratio and Mn²⁺ ion on the crystal structure, crystallite size, microstructure and magnetic properties of the produced powders were systematically studied. The results revealed that bismuth oxychloride and iron oxide were formed using chlorides sources. A single phase of BiFeO₃ was formed from as-made samples with Bi/Fe molar ratio 1.1 using nitrate sources and annealed at 500 and 600 °C for 2 h via the two pathways. The pure BiFeO₃ phase appeared as spherical and pseudocubic-like structure using the co-precipitation and the oxalic acid precursor routes, respectively. A high saturation magnetization (3.94 emu/g) was achieved for powder formed from the oxalate precursor route with Bi/Fe molar ratio 1.0 annealed at 600 °C for 2 h as the result of the formation of Bi₂₅FeO₃₉. Moreover, Mn²⁺ ion addition affected BiFeO₃ properties due to the formation of Bi₂Fe₂Mn₂O₁₀. Hence, the saturation magnetization and the coercive force of BiFeO₃ were improved substantially by substitution of Mn²⁺ ions (BiFe_1-XMn_XO₃, X = 0.1–0.2).     

Contribution de la spectrometrie mössbauer et de la spectrometrie d'absorption X A l'etude de la non-stoechiometrie de CuFe2O4

The effects of oxygen loss on the crystallographic and magnetic properties of CuFe₂O₄, ferrite have been studied by high-temperature x-ray diffraction, X-ray absorption spectrometry and Mössbauer spectrometry.In the heat-treatment under nitrogen, formation of a ferrimagnetic phase is observed with an increased content of Fe²⁺ and precipitation of CuFeO₂. Quenching after sintering leads to a mixture containing CuO and a spinel ferrimagnetic phase in which the oxygen deficiency involves the formation of Cu⁺.     

Narrowing of ferromagnetic resonance linewidth in calcium substituted YIG powders by Zr4+/Sn4+ substitution

Ca _x+y Y_3?x?y Sn _x Zr _y Fe_5?x?y O₁₂ powders were synthesized by a citric acid combustion method. The phase, microstructure and ferromagnetic resonance linewidth (ΔH) of the powders were analyzed. Pure garnet phase Y₃Fe₅O₁₂ could be obtained at 1,200 °C, except for YFeO₃ phase appearing in the sample with x = 0.5, y = 0.2. The addition of Zr⁴⁺ ion and Sn⁴⁺ ion could lower ΔH by replacing Fe³⁺ ion, which could change the a–d superexchange interaction in YIG lattice. Moreover, Zr⁴⁺ ion could promote this replacement by enlarging the lattice. However, too much addition of Zr⁴⁺ ion would bring the second phase YFeO₃. The sample of Ca_0.76Y_2.24Sn_0.7Zr_0.06Fe_4.34O₁₂ shows excellent properties which are M _s  = 6.4 emu/g, H _c  = 10.9 Oe, ΔH = 113 Gs.     

Effect of La–Zn Substitution on the Structure and Magnetic Properties of Low Temperature Co-Fired M-Type Barium Ferrite

Ba(LaZn) _x Fe_12?2x O₁₉ (0≤x≤0.5) powders with Bi₂O₃ as an additive was synthesized by a sintered route at 900 °C or 950 °C. The structure and magnetic properties of La–Zn substituted M-type barium ferrites were also investigated. When 0≤x≤0.5, only one crystal phase existed in the sample, and the morphology of the grains were shown to be gradually irregular. The little amount of La³⁺ ions and Zn²⁺ ions changed the equilibrium of Fe²⁺ and Fe³⁺ at the 2a site, which increased the Fe³⁺–O–Fe²⁺ superexchange interaction strength, and the saturation magnetization (Ms) of the samples was also improved. Meanwhile, the substitution of La³⁺ and Zn²⁺ ions and the grains’ size bought great effects on the magnetocrystalline anisotropy field. As a result, with sintering at 950 °C for 6 h, the max Ms value of the samples with x=0.1 was 67.26 emu/g, and the minimum coercivity (H _c ) value was 1718.89 Oe with x=0.3, respectively.     

Magnetic and dielectric properties of polycrystalline La doped barium Z-type hexaferrite for hyper-frequency applications

La³⁺ ion substituted barium Z-type hexaferrite, Ba_3?XLa_XCo₂Fe₂₄O₄₁ powders (X = 0.0, 0.05, 0.10 and 0.15), have been synthesized using sol gel auto-combustion method. The phase identification, microstructure, complex permittivity, complex permeability and static magnetic properties of the samples were studied using X-ray diffraction, scanning electron microscopy, vector network analyzer and vibrating sample magnetometer. The results revealed that introducing La³⁺ ion instead of Ba²⁺ ion led to an obvious enhancement of the electromagnetic properties. The crystallite size of the produced powders was slightly increased with increasing La³⁺ content. The microstructure of the produced powders appeared as hexagonal-platelet like structure. As the La content increase, the static magnetic properties were increased, the real part of complex permittivity was increased while the imaginary part was decreased. Moreover, the real part of complex magnetic permeability was decreased and the imaginary part was increased. The reasons of the obtained results were discussed on basis of electromagnetic theory.     

Preparation and Magnetic Properties of Nd3+, Al3+, Ca2+ Substituted M-Type Strontium Hexaferrites

Strontium ferrite with Nd³⁺, Al³⁺ and Ca²⁺ substitution of Fe³⁺ and Sr²⁺ ions were prepared by the conventional solid phase reaction process. The Nd³⁺ substitution shows 10 %–20 % improvement in coercivity for the substitution content less than 10 %. The Ca²⁺ substitution is favorable to the enhancement of saturation magnetization due to the accelerated reaction of Fe₂O₃ and SrCO₃. The samples with Al³⁺ substitution of Fe³⁺ show the lowest saturation magnetization, although the highest coercivity was achieved for a homogeneous grain size less than 1 μm. The combinatory substitution Nd³⁺, Ca²⁺ and Al³⁺ leads to the optimum magnetic properties with σ _s=52 A?m²/kg and H _cj=412 kA/m.     

Mechanochemical synthesis and characterization of xIn2O3��(1???x)��-Fe2O3 nanostructure system

Indium oxide-doped hematite xIn₂O₃·(1 ? x)??-Fe₂O₃ (x = 0.1?C0.7) nanostructure system was synthesized using mechanochemical activation by ball milling and characterized by XRD, simultaneous DSC?CTGA, and UV/Vis/NIR. The microstructure and thermal behavior of as obtained system were dependent on the starting In₂O₃ molar concentration x and ball milling time. XRD patterns yielded the dependence of lattice parameters and grain size as a function of ball milling time. After 12 h of ball milling, the completion of In³⁺ substitution of Fe³⁺ in hematite lattice occurs for x = 0.1, indicating that the solid solubility of In₂O₃ in hematite lattice is extended. For x = 0.3, 0.5, and 0.7, the substitutions between In³⁺ and Fe³⁺ into hematite and In₂O₃ lattice occur simultaneously. The lattice parameters a and c of hematite and lattice parameter a of indium oxide vary as a function of ball milling time. The changes of these parameters are due to ion substitutions between In³⁺ and Fe³⁺ and the decrease in the grain sizes. Ball milling has a strong effect on the thermal behavior and band gap energy of the as-obtained system. The hematite decomposition is enhanced due to the smaller hematite grain size. The crystallization of hematite and In₂O₃ was suppressed, with drops of enthalpy values due to the stronger solid?Csolid interactions after ball milling, which caused gradual In³⁺?CFe³⁺ substitution in hematite/In₂O₃ lattices. The band gap for hematite shifts to higher energy value, while that of indium oxide shifts to lower energy value after ball milling.     

The effect of Cu content on the structure of Ni1−xCuxFe2O4 spinels

A series of Ni_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 °C. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 °C to 350 °C. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu²⁺ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe₂O₄, showing different surface oxygen species from the spinel and CuO. Cu²⁺ substitution favors the occupancy of A-sites by Fe³⁺.     

Optical and electrical properties of Ba1−x Sr x TiO3 nanopowders at different Sr2+ ion content

Barium strontium titanate (BST) Ba_1?x Sr _x TiO₃ nanopowders have been successfully synthesized using oxalate precursor route. The effect of Sr²⁺ ion content from 0.3 to 0.7 on the crystal structure, crystallite size, microstructure, electrical and optical properties was systematically studied. The results revealed that well crystalline single BST phase was formed by annealing the oxalate precursor at 1,000 °C for 2 h. The crystallite size of the BST powders was decreased with increasing the Sr²⁺ ion molar ratios. The crystallite size was decreased from 56.0 to 33.1 nm when the Sr²⁺ ion content increased from 0.3 to 0.7. Additionally, the lattice parameter (a), unit cell volume and X-ray density of BST ware decreased whereas the porosity, % were increased with Sr²⁺ ion concentration. The BST phase appeared as cubic-like structure. The spectrophotometer measurement results demonstrated that the room temperature band gap energy varied with the Sr²⁺ ion composition x. The band gap energy was shifted to low energy and it was decreased from 3.6 to 3.2 eV with increasing the Sr²⁺ ion content from 0.3 to 0.7. Moreover, the DC resistivity was enhanced with increasing the Sr²⁺ ion ratio. The dielectric response obtained for the stressed samples corresponds to a true resonance rather than a dispersion process with a characteristic frequency around 1 GHz at room temperature. However, the peaks commonly observed at GHz frequency were changed with varying the Sr²⁺ ion composition. The high imaginary components of dielectric permittivity for x = 0.3 was found at higher frequency region around 1.6 GHz compared with the samples with x values of 0.5 and 0.7 in which the frequency regions were around 1.25 and 1.15 GHz, respectively.     

Effect of potassium on the structure and catalytic properties of K<Subscript>1.2</Subscript>Cu<Subscript>0.4</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>

We have studied the structural properties of the phase K_1.2Cu_0.4Fe₂O₄ and the effect of potassium on its catalytic activity for oxidation of carbon. The results demonstrate that the potassium-doped phase differs from the undoped ferrite CuFe₂O₄ in linear dimensions of its unit cell, high density of structural defects, and low-temperature activity and activation energy for the catalytic process. Contact interaction between K_1.2Cu_0.4Fe₂O₄ and carbon in the temperature range 240–420°C leads to the reduction of Cu²⁺ to Cu⁺ and the formation of Cu₂O, CuFeO₂, and K₂Fe₄O₇. Testing results for the phases identified indicate that the catalytic processes in the presence of K₂Fe₄O₇ and K_1.2Cu_0.4Fe₂O₄ are identical.     

Effect of aluminum substitution on microstructure and magnetic properties of electrospun BaFe12O19 nanofibers

BaFe_12?x Al _x O₁₉ nanofibers (x = 0–2.0) with average diameter 110 nm have been prepared via the electrospinning and subsequent heat treatment at 1100 °C for 2 h. Individual BaFe₁₂O₁₉ nanofibers were composed of numerous nanocrystallites stacking alternatively along the long axis of fiber and the single crystallites on each nanofibers had random orientations. With increasing Al³⁺ ions substitution contents from 0 to 2.0, the diameter and morphology of nanofibers were almost no change. However, the lattice parameters decreased due to Fe³⁺ ions substituted by smaller Al³⁺ ions and the average grain size calculated by the Scherrer’s equation reduced from 47 to 42 nm. The crystallites possessed a hexagonal plate-like shape at x = 0 while they became rod-like with various Al³⁺ ions substitution. The X-ray diffraction patterns show that single-phase barium hexaferrite was formed when Al³⁺ ions substitution contents were less than and equal to 1.0, while other impurity phases were detected when they were more than 1.0. The chemical analysis shows that the element Al was all incorporated into the lattice of BaFe₁₂O₁₉ and evenly distributed throughout the BaFe_12?x Al _x O₁₉ nanofibers. The magnetic testing shows that the saturation magnetization (M _s) decreased obviously from 63.92 to 29.70 A m²/kg, while coercivity (H _c) increased significantly from 288.2 to 740.7 kA/m with increasing Al³⁺ ions substitution.     

Thin films preparation by rf-sputtering of copper/iron ceramic targets with Cu/Fe = 1: From nanocomposites to delafossite compounds

In the Cu-Fe-O phase diagram, delafossite CuFeO₂ is obtained for the Cu^I oxidation state and for the Cu/Fe = 1 ratio. By decreasing the oxygen content, copper/spinel oxide composite can be obtained because of the reduction and the disproponation of cuprous ions. Many physical properties as for instance, electrical, optical, catalytic properties can then be affected by the control of the oxygen stoichiometry.In rf-sputtering technique, the bombardment energies on the substrate can be controlled by the deposition conditions leading to different oxygen stoichiometry in the growing layers.By this technique, thin films have been prepared from two ceramic targets: CuFeO₂ and CuO + CuFe₂O₄. We thus synthesized either Cu⁰/Cu_xFe_1−xO₄ nanocomposites thin films with various Cu⁰ quantities or CuFeO₂-based thin films.Two-probes conductivity measurements were permitted to comparatively evaluate the Cu⁰ content, while optical microscopy evidenced a self-assembly phenomenon during thermal annealing.     

Microstructure and dielectric properties of Ca1–3/2xBixCu3Ti4O12 (x = 0, 0.05, 0.10, 0.15 and 0.20) ceramics

Influence of bismuth substitution on calcium site in CaCu₃Ti₄O₁₂ has been investigated. Compositions of Ca_1-3/2xBi_xCu₃Ti₄O₁₂ (x = 0, 0.05, 0.10, 0.15 and 0.20) were fabricated by solid-state sintering method. Crystal structure is remained cubic. X-ray diffraction indicates the presence of secondary phase of CuO in CCTO ceramics. Bismuth doping restrains the formation of CuO phase apparently. The grain size of CaCu₃Ti₄O₁₂ ceramics was greatly decreased by Bi³⁺ doping, resulting from the ability of bismuth to inhibit the grain growth. The dielectric and electric properties of CCTO ceramics were found to be influenced by bismuth doping. The fitting results of the complex impedance spectra showed an increase of the resistance of grain and grain boundary by bismuth substitution. Ca_0.70Bi_0.20Cu₃Ti₄O₁₂ showed the highest dielectric constant in the low frequency range. A modest composition such as Ca_0.85Bi_0.10Cu₃Ti₄O₁₂ expressed the optimized dielectric properties of higher dielectric constant (1.3 × 10⁴) and lower dielectric loss (0.06) than pure CCTO. The low and high temperature dielectric loss spectra demonstrate the interfacial polarization of the initial and secondary oxygen ionization, relating with the grain and grain boundary (the electrode contact for Ca_0.70Bi_0.20Cu₃Ti₄O₁₂) respectively.