Pure Spinel Research Articles

Investigation of temperature sensing based on luminescence intensity ratiometric and lifetime of Zn0.9Mn0.1Al2O4:Cr3+ phosphors with various reducing time

Zn0.9Mn0.1Al2O4:Cr3+ phosphors with pure spinel structure were fabricated by using co-precipitation method. The influence of reducing time on the structure, photoluminescence and temperature sensing properties were investigated by using X-ray diffraction (XRD), electron paramagnetic resonance (EPR) and photoluminescence (PL). With the reducing time increasing, the diffraction peak reveals a shift toward lower angle, and the isolated six refined peaks of EPR assigned to Mn2+ in spinel lattices reveal a large increasing overlap, indicating the increasing concentration of Mn2+. A red emission assigned to 2Eg→4A2g of Cr3+ is observed, but its intensity is very tiny in the as-synthesized Zn0.9Mn0.1Al2O4 phosphors, and with reducing time increasing, the emission intensity is enhanced sharply. The energy level of 2Eg is split into 2E(2 A‾) and 2E(E‾) corresponding to 687 nm (R1) and 689 nm (R2) emissions due to the high crystal field in ZnAl2O4 lattices. The emission assigned to Mn2+-Vo (Oxygen vacancy) at 530 nm reveals a strong temperature dependence, and the highest relative sensitivity of 2.55 %K−1 is achieved based on the luminescence integral intensity ratio of I530nm/Mn2+, which is higher than that based on the lifetime of 512 nm emission peak assigned to Mn2+ and based on the luminescence integral intensity ratio of the excitation peaks of I427nm/I530nm, indicating that the potential application in multi-reading temperature nanoprobe.

Structural and elastic properties of tetragonal nano-structured copper ferrite

Abstract The surge of interest in ferrimagnetic materials over the years has been driven by their fascinating multifunctional properties. The elastic properties of these materials are a subject of much interest and vital importance due to their wide range of technological and industrial applications. In the present work, the structural and elastic properties of tetragonal copper ferrite (CuFe2O4) nanoparticles synthesized by a citrate assisted sol-gel auto combustion technique have been investigated. The nanocrystalline powder of copper ferrite was characterized by using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and UV–Visible spectroscopic techniques. The X-ray diffraction pattern revealed pure spinel structure of copper ferrite nanoparticles with Jahn–Teller tetragonal distortion. The band gap of copper ferrite nanoparticles was found to be 3.14 ± 0.03 eV using the diffuse reflectance spectra. The values of elastic moduli (Young’s modulus (E) = 186.3 ± 0.5 GPa, bulk modulus (B) = 124.1 ± 0.3 GPa, and rigidity modulus (G) = 74.4 ± 0.2 GPa) and Debye temperature (θ D = 500.5 ± 0.5 K) suggest that the synthesized nano-structured copper ferrite is a promising candidate for high temperature and high pressure applications.

Effect of Ni substitution and annealing temperature on structural and magnetic properties of MnZn-Ferrites: Cytotoxicity study of ZnO and SiO2 coated core shell structures

Magnetic spinel ferrite nanoparticles (NPs) have a broad scope of applications based on their structural properties, including in lithium-ion batteries, catalysts, electrochemical energy storage, drug delivery, magnetic hyperthermia, and photothermia. In this study, we investigated the structure, crystallographic phase formations, and magnetic properties of Ni-substituted MnZn ferrites (MZFs), Mn(0.6-x)Zn(0.4-y)Ni(x+y)Fe2O4 (x = 0–0.6, y = 0; y = 0–0.4, x = 0) compositions of as-prepared (AP) and air annealed (350–1200 °C) samples. All AP NPs exhibited a pure spinel structure. Ni-MZF compositions annealed at 600 °C had high α-Fe2O3 secondary phase content in Ni-MZFs (Ni substituted for Zn), whereas Ni-MZFs with x = 0.4 (Ni substituted for Mn) had no impurities, and its magnetization (50 emu/g) was enhanced compared with that of the other samples. X-ray photoelectron spectroscopy revealed that Fe3+ cations were present in tetrahedral and octahedral sites. The single spinel phase reappeared with improved crystallinity in all Ni-MZFs by annealing at 1200 °C and exhibited superior magnetization (60–73 emu/g) compared with that of MZF (35 emu/g). Additionally, the spinel phase was stabilized in the ZnO- and SiO2-coated Ni-MZF core shell structures annealed at 700 °C with higher magnetization than MZF. Moreover, Ni-MZF core shell structures exhibited biocompatibility and may have biomedical applications.

Synthesis, characterizations, and magnetic behavior of novel (CuNiTiZnFe)3O4 high entropy spinel oxide

In this report, a modified solid-state synthesis technique is optimized to synthesize a single spinel phase for a novel (CuNiTiZnFe)3O4 High Entropy Oxide (HEO) and studied for magnetic behavior. Three different approaches were adopted for the synthesis of pure spinel HEO. In the first approach, The initial mixture of constituent oxides was admixed, and sintered at 1050 °C for 20 h. For the second and third approaches, the mixture of constituent oxides was ball-milled for 2 h, and 10 h separately, followed by sintering at 1050 °C for 20 h. A small amount of undiffused constituent oxide peaks are present in both the first and second approaches. However, the sample synthesis through 10 h milling followed by sintering has single spinel (CuNiTiZnFe)3O4 HEO phase. The single spinel HEO phase formation was confirmed through the le-Bail refinement. The lattice parameter for the well-fitted XRD pattern is 8.415161 A°. Further, the investigation was focused on the magnetic behavior of the single spinel HEO phase. The value of magnetization and coercivity is 16.11 emu/g and 10.66 Oe, respectively. The synthesized HESO has typical ferrimagnetic nature and has the second-highest value of Ms reported so far for HEOs. The ionic states of different cations present in the (CuNiTiZnFe)3O4 HESO were also investigated through X-ray photoelectron Spectroscopy. XPS analysis reveals that Fe and Ni are in the +3 and + 2 states, Cu and Zn are in the +2 states, and Ti is in the +4 states.

Bi3+ and V3+ co-substituted Ni-Co spinel ferrites: Synthesis, optical, magnetic characterization and hyperfine interaction

Ni0.5Co0.5VxBixFe2-2xO4 spinel ferrite nanoparticles with composition (x = 0.00, 0.02, 0.04, 0.06 and 0.08) (CoNiVBiFeO (x = 0.00–0.08) SFNPs) were well fabricated hydrothermally. The consequence of co-substitution of both Bi3+ and V3+ ions on structure, morphology, and magnetic features of Ni0.5Co0.5Fe2O4 SFNPs were studied using XRD (X-ray diffractometry), scanning (SEM) and transmission (TEM) electron microscopies along with EDX, XPS (X-ray photoelectron spectroscopy), VSM (vibrating sample magnetometry) and Mossbauer spectroscopic techniques. The pure spinel ferrite (SFs) phase was approved via XRD. The morphology of SFNPs were revealed by SEM and TEM. Hyperfine parameters are determined from fitting room temperature Mössbauer spectra. The V3+ and Bi3+ ions occupy mainly at B site. The isomer shift values are coupled with the characteristics of the high spin Fe3+ ion. The influence of V3+ and Bi3+ ions co-doping on the magnetic features of Ni-Co SFNPs has been also investigated at 300 and 10 K. The saturation magnetization (Ms), remanence (Mr), coercive field (Hc), and Bohr magneton number (nB) are extracted from the recorded M-H hysteresis loops. Nanomagnetic materials with x content of 0.02, 0.08, and 0.10 exhibited superparamagnetic (SPM) behavior, whereas other products with x content of 0.00, 0.04, and 0.06 displayed soft ferrimagnetic behavior at ambient temperature. The different prepared nanoferrites displayed hard ferrimagnetic characteristic at 10 K. The Ms and Mr values are decreased as result of V3+ and Bi3+ ions co-doping. However, Hc does not show a monotonic trend. The fluctuations in magnetic moments of ions, super-exchange coupling, and distribution of cations are correlated with the changes in magnetic parameters to explain their variations.

Electrochemical performance and large positive–negative magnetodielectric coupling in iron chromite spinels

• Current work is one of its kind study suggesting a material that can be used to fabricate a device that can simultaneously store memory and energy. • Low cost sol–gel method is used to synthesize iron chromite nanocrystals by varying Fe/Cr ratio. • Spinel phase i.e. FeCr 2 O 4 is observed at Fe/Cr ratios of 0.45, 0.6 and 0.65. • Magneto dielectric (MD) studies confirm positive MD constant at 0.45, 0.6 & 0.65 Fe/Cr ratios. • The galvanostatic charging/discharging behavior shows capacitive behavior of FeCr 2 O 4 samples. • The electrochemical results suggest that synthesized nanocrystals have potential for energy storage system. Spinel ferrites with remarkable electrochemical performance and magnetodielectric (MD) coupling are promising candidates for energy storage and spintronic devices. This study focuses on structural phases, dielectric and magnetic polarization along with magnetodielectric (MD) coupling and electrochemical response of Fe-Cr spinels. Low cost sol–gel method is used to synthesize iron chromite nanopowders. Iron to chromium (Fe/Cr) ratio is varied in the range of 0.2–0.65 (with interval of 0.05). XRD patterns confirm the formation of phase pure FeCr 2 O 4 at Fe/Cr ratios of 0.45, 0.6 & 0.65. Amorphous behavior is observed at Fe/Cr ratios of 0.2, 0.25, 0.5 & 0.55. Mixed phases are observed at 0.3, 0.35 & 0.4 Fe/Cr ratios. Formation of pure spinel phase at Fe/Cr ratio of 0.45 results in high saturation magnetization of 9.2 emu/g. High grain boundary resistance (189.62kΩ) and high dielectric constant (∼83.38 at log f = 5.0) along with low tangent loss (0.00423 at log f = 5) are observed at Fe/Cr ratio of 0.45. Magneto dielectric studies confirm positive magneto dielectric constant (MDC) of synthesized nanopowders at 0.45, 0.6 & 0.65 Fe/Cr ratios. Cyclic voltammetry is performed at constant potential window. Oxidation/reduction process leads to the pseudo-capacitive response of the material. The cyclic voltammetry curves show specific capacitance of 156 Fg −1 , 144 Fg −1 and 152 Fg −1 at scan rate of 25 mV/s at Fe/Cr ratios of 0.45, 0.6 & 0.65 of FeCr 2 O 4 nanopowders, respectively. The galvanostatic charging/discharging behavior shows capacitive behavior of FeCr 2 O 4 nanopowders. The electrochemical results suggest that synthesized nanopowders have potential for energy storage system.

The influence of reaction and annealing temperature on physical and magnetic properties of CuFe2O4 nanoparticles : Hydrothermal method

Pure copper ferrite nanoparticles (CuFe2O4 NPs) were synthesized by using a simple hydrothermal method and annealed at different levels of temperatures. The single–phase cubic spinel structure was confirmed by X-ray diffraction pattern and average crystallite size was found to increase from 34 to 42 nm as the annealing temperature increases. FT-IR spectra confirmed metal oxides Fe-O and Cu-O, the formation of pure spinel magnetic copper ferrite nanoparticles. The five Raman active modes of vibrations confirmed the cubic structure of prepared yield (A1g + Eg + 3T2g). The average particle size identified by TEM analysis exists within the nano range with cubic structures. The magnitudes of the zeta potential indicated the potential stability and surface charge of the nanoparticles. The pore size was estimated by BJH technique and the obtained distribution as 18.5 nm in diameter. The optical study revealed the decreasing nature of the bandgap with increasing annealing temperature. The dielectric parameters were analysed with varying frequency range and it was observed that decreasing nature of dielectric loss is suitable for microwave application. The influence of annealing temperature revealed the increase of saturation magnetization, remanence and coercivity owing to the increased crystallite size. The electrochemical analyses of as-prepared and the annealed (750 °C) CuFe2O4 NPs exhibited high specific capacitance at a low scan rate which indicates the good result for supercapacitor application.

Structural, dielectric and gas sensing properties of gadolinium (Gd3+) substituted zinc-manganese nanoferrites

Gadolinium (Gd3+) substituted zinc manganese ferrite nanoparticles with nominal compositions Zn0.7Mn0.3GdxFe2-xO4 (where x = 0.000; 0.025; 0.050; 0.075; 0.100) were successfully synthetized using co-precipitation method. The synthetized powders were calcined at 500 °C and furthermore pressed into pellets and thermally treated at 650 °C for a second time to obtain a more compact material. For the 500 ℃ thermal treated samples, X-ray analysis revealed the formation of pure spinel ferrite phase, meanwhile for the 650 ℃ thermal treated samples secondary phases appear which indicate that some of Gd3+ ions aren’t able to remain in the structure of ferrite. The morphology of samples was investigated using scanning electron microscopy (SEM) and the images show agglomerated spherical nanoparticles within 20–30 nm size range. The magnetization curves recorded in ±10 kOe range indicate a superparamagnetic behavior of the synthetized ferrite samples. At low frequencies, the Gd3+ substituted ferrite samples corresponding to x = 0.050, 0.075 and 0.100 exhibit a resonant behavior of the dielectric losses dependence, while at high frequencies the lowest value was found for the sample with x = 0.025. The introduction of Gd3+ ions in the ferrite structure leads to a non-monotonous variation of AC electrical conductivity, which decrease from 2.55 x10−6 S/m to 3 x10−7 S/m. The ferrite samples have shown a good and reproducible response to the saturated acetone vapors and the highest sensitivity value (53%) was obtained for Zn0.7Mn0.3Gd0.025Fe1.9O4 ferrite sample. The response and recovery time varies between 36 and 56 s, respectively 80–116 s and both of these are independent of Gd3+ content.

Catalytic adsorptive removal of toxic compounds from water using motifs of Ce doped Co3O4/RGO nanohybrids

Physical aspects of bimetallic transition metal oxides are sensitive to morphology, type and composition of dopant metal cations and cation distribution in the lattice of parent oxide. Here in this study, motifs are fabricated by a combination of rare earth (Ce3+) metal doping in the cobalt oxide and hybridization with Graphene oxide (GO) using metal organic frameworks (MOF). Pure spinel phase crystalline mesoporous nanohybrids fabricated as polyhedrons possess a large specific surface area of 487 m2g-1. They found highly efficient for degradation of nitrophenol (NP) and tetracycline (TC; an antibiotic) from water in the absence of external agents. Nanohybrid shows effective adsorption, as nitrophenol disintegrated while diffusing on the surface of RGO/Co2.5Ce0.5O4 hybrid and completely removed in 6 min from water. Role of Ce3+ ions and GO, both is evaluated on the degradation of NP and TC. Cation pairs (Co3+/Co2+) and (Ce3+/Ce4+) played critical role for enhanced removal of compounds.

A comparative study of different oxidation states of raw materials on the properties of a novel medium-entropy Co2.77Mn1.71Fe1.10Zn0.42O8 thermistor materials

In recent years, high entropy oxides (HEOs) have aroused extensive attention due to their potential applications in catalysis, energy storage and thermal protection. However, as an emerging material, the synthesis, properties and applications of HEOs have yet to be further developed. Herein, we reported a novel non-equiatomic medium-entropy Co2.77Mn1.71Fe1.10Zn0.42O8 oxides for temperature sensing applications by using the different oxidation states of cobalt and iron as raw materials. Results indicate that the prepared multi-component samples present a pure spinel phase, highly dense microstructure, and typical negative temperature coefficient characteristics. Our results also suggest that the different oxidization states of cobalt and iron of raw materials induce obvious influences on resistivity and aging stability. In particular, the medium-entropy oxides can exhibit excellent superior aging stability (the resistance drift ≤0.2% after accelerated aging in 125 °C for 600 h) by a suitable selection of the starting oxides. This work will provide new material design strategies for sensors or other electronic devices and guidance on the raw material selection from laboratory research to industrial production processes.

Safe extended-range cycling of Li4Ti5O12-based anodes for ultra-high capacity thin-film batteries

Lithium titanium oxide thin films are increasingly popular anode materials in microbatteries and hybrid supercapacitors, due to their improved safety, cost, and cycle lifetime. So far, research efforts have mainly focused on the pure spinel phase Li4Ti5O12 (LTO) and only a small fraction is dedicated to a broader spectrum of titanium-based metal oxide thin films. In this work, pulsed laser deposition is used in a multilayer approach by alternating LTO and Li2O ablations to create a heterogeneous landscape in the titania-based micro-anodes. This rich microstructure enables the safe extension of the accessible electrochemical window down to 0.2 V. This leads to extraordinary high specific capacities of 250–300 mAh/g at 1 C, maintaining a stable discharge capacity of 180 mAh/g at 16 C. Operando spectroscopic ellipsometry and Raman spectroscopy are used to track optical and structural changes as a function of the discharge voltage down to 0.01 V. A kinetically limited degradation mechanism based on the effective trapping of Li-ions at the octahedral 16c positions is proposed when cycling in the range of 0.2–0.01 V. In essence, our work contributes to titania-based nanoshapes as anodes of increased specific capacity due to a higher Li-site occupation, while maintaining their good stability and safety.

Deposition, Characterization, and Performance of Spinel InGaZnO4

Polycrystalline indium–gallium–zinc oxide (IGZO) in the spinel phase was obtained by physical vapor deposition (PVD), using reactive sputtering from an IGZO target with In/Ga/Zn = 1:1:1 composition. The initial growth of spinel IGZO is investigated by X-ray diffraction measurements after annealing the film. Deposition of spinel IGZO initially starts as a mixed amorphous/c-axis-aligned crystalline (CAAC) film, after which a metastable spinel IGZO is formed. Using a template of polycrystalline spinel Ga2ZnO4, the growth of the spinel phase is immediately achieved and enables the electrical characterization of pure spinel IGZO channels in scaled thin-film field-effect transistors. The average effective channel field-effect mobility of spinel IGZO of 50 ± 10 cm2/(V s) is slightly higher than amorphous IGZO in the same devices. This is in line with a slightly lower effective electron mass, as is calculated with density functional theory. The calculated total energies and band gaps have similar values to CAAC-IGZO. This metastable nature identifies spinel IGZO as an intermediate phase before the onset of CAAC-IGZO formation during PVD. Spinel IGZO is an interesting alternative to amorphous IGZO (a-IGZO) and CAAC-IGZO because of potentially higher robustness to oxygen vacancy formation.

Sonochemical synthesis of Mn0.5Zn0.5ErxDyxFe2-2xO4 (x ≤ 0.1) spinel nanoferrites: Magnetic and textural investigation

Mn0.5Zn0.5ErxDyxFe2-2xO4 (x ≤ 0.1) spinel nanoferrites (SNFs) were fabricated successfully via Ultrasonic irradiation. Structural and morphological analysis were investigated via X-ray diffraction diffractometer (XRD), scanning (SEM) and transmission electron microscopes (TEM), Fourier-transform infrared spectroscopy (FTIR), and Surface Area Analyzers (BET). XRD showed the formation of highly pure Mn-Zn spinel ferrite phase with an average crystallite size within 19–26 nm range. The formation of spherical nanoparticles with small particles size was also approved by SEM and TEM techniques. Magnetization response to the magnetic field applied (M vs H) and temperature and (M vs T under ZFC and FC modes), were investigated to understand the impact of Er and Dy co-doping mechanism on the magnetic features of MnZn SNFs. The findings through the magnetization measurements demonstrate superparamagnetic (SPM) behavior with single magnetic domain particles for different prepared products and with no coercivity (Hc) and remanence (Mr) at RT and at temperatures above the TB (blocking temperature). At lower temperatures below TB, it has been illustrated that the prepared SNFs have ferrimagnetic (FM) behavior with the existence of coercivity (Hc) and remanence (Mr). The calculated squareness (SQR = Mr/Ms) at T = 10 K are ranging between 0.14 and 0.29, which are below the predicted value of 0.5, reflecting the MMD nature in different prepared SFNPs at T = 10 K. In comparison to pristine product, the saturation magnetization (Ms) initially increased for lower co-doping contents of Er and Dy up to x = 0.04 and then decreased by the further Er and Dy co-doping concentrations (x > 0.04).

Influence of Ce3+ on the Structural, Morphological, Magnetic, Photocatalytic and Antibacterial Properties of Spinel MnFe2O4 Nanocrystallites Prepared by the Combustion Route

The present work describes the effect of Ce3+ ion doping on the structural, morphological, and magnetic properties of spinel manganese ferrite (MnFe2O4) nanocrystallites (NCs) using various instrument techniques. Rare earth element (REE) Cerium (Ce3+) doped MnFe2O4 NCs were prepared by a simple microwave combustion technique. In the present scenario, ferrites are widely used for photocatalytic dye degradation and antibacterial applications. Aiming to achieve this, we prepared Ce3+ doped MnFe2O4 NCs by microwave combustion method and urea as burning agent and the obtained powder samples were characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), high resolution scanning electron microscope (HR-SEM), high resolution transmission electron microscope (HR-TEM) and vibration sample magnetometer (VSM) techniques. The pure spinel phase formation was confirmed by XRD analysis. FTIR spectra show two prominent absorption bands under 1000 cm−1, which confirms the formation of the spinel structure. HR-SEM and HR-TEM pictures demonstrated a sphere-shaped morphology and also expose the combination and agglomeration of grains, which are mostly due to the magnetic characteristics of the samples. The magnetic properties of the synthesized MnCexFe2−xO4 (x = 0.0, 0.1, 0.3, and 0.5) NCs were studied by VSM analysis at room temperature (RT) shows ferromagnetic behavior. The photodegradation results showed that MnFe2O4 and Ce doped MnFe2O4 NCs have a higher potential to degrade methylene blue (MB) and the sample MnCe0.3Fe1.7O4 NCs showed superb photocatalytic performance (91.53%) compared to other samples. The antibacterial activities of Gram-positive S. aureus, B. subtilis and Gram-negative K. pneumonia and E. coli were investigated using pure and Ce3+ substituted MnFe2O4 NCs and a higher activity for MnCe0.3Fe1.7O4 NCs than other samples was observed, which indicated that they can be used in biomedical applications.

Mononuclear Transition Metal Cymantrenecarboxylates as Precursors for Spinel-Type Manganites.

Novel mononuclear cymantrenecarboxylate complexes of transition metals, [Co(H2O)6](CymCO2)2·4H2O (Cym = (η5-C5H4)Mn(CO)3) (1), [Ni(H2O)6](CymCO2)2·4H2O (2), [Zn(H2O)6](CymCO2)2·4H2O (3), [Co(CymCO2)2(imz)2] (imz = imidazole, 4), [Co(CymCO2)2(bpy)2]·2PhMe (bpy = 2,2′-bipyridyl, 5), [Ni(CymCO2)(bpy)2(H2O)][CymCO2]·0.5MePh·2H2O (6), [Cu(CymCO2)2(imz)2] (7), and [Cu(CymCO2)2(bpy)(H2O)] (8), were obtained and characterized by single-crystal X-ray analysis. Complexes 1–3 are isostructural. Magnetism of the Co complexes 1, 4, and 5 was studied; it was shown that they exhibit the properties of field-induced single-molecule magnets with magnetization reversal barriers (ΔE/kB) of 44, 13, and 10 K, respectively. Thermal decomposition of complexes 1–8 was studied by means of DSC and TGA methods. The final products of thermolysis of 1–6 in air, according to powder XRD data, are the pure spinel phases MMn2O4; for the cases of copper complexes, the mixtures of CuMn2O4 and CuO were found in the products.

The synthesis of zinc ferrite spinel: Determination of pH value in the co-precipitation step

Zinc ferrite (ZnFe2O4) nanomaterial can be facilely and conveniently synthesized via the co-precipitation method from aqueous Zn2+ and Fe3+ salt solutions using sodium hydroxide as the precipitant. However, zinc hydroxide is amphoteric and can be soluble at low and high pH values; therefore, the study on pH for simultaneous precipitation of Fe3+ and Zn2+ to achieve pure ZnFe2O4 spinel is essential. In the present study, we elaborate a theoretical equation expressing the relationship between the zinc concentration in complex formation and pH value in the co-precipitation step. Since then, we synthesized ZnFe2O4 spinel and analyzed the products via various techniques such as thermoanalysis (TG-DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectra to investigate the appropriate pH for simultaneous precipitation of Fe3+ and Zn2+. The results indicate that in a wide range of pH values, from 7 to 12, ZnFe2O4 single-phase spinel ferrite structure is formed after calcination of the precipitate at 800 °C, the average particle sizes (SEM, nm) of ZnFe2O4 samples are in the range of 59.5 nm–85.5 nm (but is non-linear change), and their bandgap values are similar, around 1.96 eV. However, the unwanted appearance of α-Fe2O3 phase, the shifting in peak position and the decrease in intensity in the XRD pattern of the spinel products synthesized at pH of 6 and 13, respectively, reflect that the stoichiometric ratio of Zn2+ to Fe3+ in the spinel products is not achieved to 1:2. Such results provide a fundamental basis for choosing the appropriate pH in synthesizing ZnFe2O4 nanoparticles with orientationally structural and optical characteristics.

Structural and Electrochemical Properties of NiFe2-xCuxO4 Spinel for Oxygen Evolution Reaction

Developing new material oxides catalysts for the oxygen evolution reaction in alkaline media is important to enhance the efficiency of the water-splitting process. For this purpose, the effect of copper doping on the structural, morphological, and catalytic properties of NiFe2CuO4 oxides for the oxygen evolution reaction has been investigated. X-ray diffraction analysis of samples calcined at 1000 °C shows that the pure spinel structure was obtained in the range 0 ≤ x ≤ 0.4. The FTIR spectra confirm the presence of the metal-oxygen bond of M-O in the tetrahedral and octahedral sites of the spinel structure. Scanning electron microscopy (SEM) shows that the calcined powders have a compact and dense surface and pronounced agglomeration. The OER results indicate that the NiFe2O4 electrode exhibits a higher performance with the current density of 26 mA.cm−2 at 0.55 V and a small Tafel plot of 68 mV.dec−1. Further investigations also accounted for the degradation of electrocatalytic activity with increasing copper content.

Effects of Ni2+ concentration on the composition, structure, magnetic properties, and DC-bias superposition characteristics of NiCuZn ferrites

NixCu0.2ZnyFe1.98O4 (x = 0.16, 0.26, 0.35, 0.43, 0.50; y = 0.8−x) ferrites were prepared via solid-state reaction. The influence of Ni2+ concentration on ferrites composition, microstructure, magnetic properties and DC-bias superposition characteristics was studied by XRD, SEM, XPS, and VSM. Then, the effect of magnetic properties on the DC-bias superposition characteristics was analyzed. The results showed that the ferrites sintered at 900 °C for 3 h were all in pure spinel phase with an average grain size of 7.5 μm and a relative density of about 5.15 g cm−3. With the increase in Ni2+ concentration, the saturation magnetization (Ms) and coercivity (Hc) of ferrites increased, but the magnetocrystalline anisotropy constant (K1) first increased and then decreased. And the Ms, Hc, and K1 of the specimen with x = 0.43 were 63.62 emu·g−1, 27.36 Oe, and 1813.17 Oe·emu·g−1, respectively. In particular, the specimen of x = 0.50 achieved the best DC superposition characteristics, where the H70% was about 220 A m−1. The incremental permeability of the specimens decreased rapidly at a bias magnetic field <400 A m−1. The variation mainly originated from the domain wall displacement, and the rate of decrease was influenced by both Ms and K1. At a bias magnetic field ≥400 A m−1, the incremental permeability of the specimens decreased slowly, mainly because the number of domain walls decreased until disappearing, and the specimens tended to become a single domain structure. And the rate of decrease of incremental permeability was mainly affected by K1.

Influence of Nd3+ substituted Co0.5Ni0.5Fe2O4 ferrite on structural, morphological, dc electrical resistivity and magnetic properties

Solid-state reaction method was incorporated for the preparation of rare earth Nd3+ substituted Co-Ni ferrite materials Co0.5Ni0.5Fe2-xNdxO4 where × = 0.0, 0.03, 0.06, and 0.09. They were characterized by XRD, SEM, FTIR, Raman spectrometer, DC electrical resistivity, and Vibrating sample magnetometer studies for their structural, morphological, infrared dc electrical resistivity, and magnetic properties.XRD studiesof all the samples revealed a single-phase pure cubic spinel structure. Thecrystallite size decreases from 44 nm to 32 nm and lattice constant increases with Nd3+content. The grain size was found in the range of 2–3.5 µm. FTIR supports the XRD results. Showing two absorption bands near (octahedral site) 400 cm−1and (tetrahedral site) 600 cm−1. The DC resistivity is increased with Nd3+ content increases shows their semiconducting nature and activation energy varies from 0.52 eV to 0.62 eV. The saturation magnetization increases from 51.22 emu/g to 56.33 emu/g with the increase in doping. Their coercivity depends on the particle size and it decreases from 365 Oe to 153 Oe.

Microstructural and Optical Properties of MgAl2O4 Spinel: Effects of Mechanical Activation, Y2O3 and Graphene Additions.

Magnesium aluminate and other alumina-based spinels attract attention due to their high hardness, high mechanical strength, and low dielectric constant. MgAl2O4 was produced by a solid-state reaction between MgO and α-Al2O3 powders. Mechanical activation for 30 min in a planetary ball mill was used to increase the reactivity of powders. Yttrium oxide and graphene were added to prevent abnormal grain growth during sintering. Samples were sintered by hot pressing under vacuum at 1450 °C. Phase composition and microstructure of sintered specimens were characterized by X-ray powder diffraction and scanning electron microscopy. Rietveld analysis revealed 100% pure spinel phase in all sintered specimens, and a decrease in crystallite size with the addition of yttria or graphene. Density measurements indicated that the mechanically activated specimen reached 99.6% relative density. Furthermore, the highest solar absorbance and highest spectral selectivity as a function of temperature were detected for the mechanically activated specimen with graphene addition. Mechanical activation is an efficient method to improve densification of MgAl2O4 prepared from mixed oxide powders, while additives improve microstructure and optical properties.