Cobalt Spinel Research Articles

Electrospinning of multiferroic CoFe2O4@ Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 nano-structured fibers via two different routes

Multiferroic composite materials have attracted a lot of attention for their excellent ferroelectric and ferromagnetic properties. For the first time one-dimensional core-shell structure of CoFe2O4/Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (CFO@BZCT) multiferroic composite was synthesized by electrospinning. The effect of electrospinning routes on the composite fibers properties was investigated. To do so, two different routes were utilized: the electrospinning of core and shell solutions using coaxial nozzle and the electrospinning of BZCT solution containing CFO fibers (with three different concentrations of 2, 4 and 8 g/100 ml solution). The fiber morphology was maintained for all samples in calcination temperatures up to 900 °C. Spinel cobalt ferrite and perovskite BZT-0.5BCT phases were crystallized for calcined composites. The nano and core-shell structure of composites were confirmed by the TEM analysis. Magnetoelectric coupling of CFO and BZCT phases was investigated by the temperature-dependent SQUID measurement, where a ferroelectric phase transformation at 100 °C induced magnetization changes. Low saturation magnetization and dielectric constant of 6.7 emu/g and 300 ± 10 were obtained for the sample synthesized by the first method while these values rose to 36.8 emu/g and 400 ± 30 respectively for the second method. A comparison of the two methods exhibited a larger fiber diameter, porous fibers and lower ferroic properties for the sample synthesized by the first method.

Влияние ультразвуковой обработки прекурсора на синтез, характеристики текстуры и электропроводность NiCo2O4

The high-dispersed powder−precursors of nickel−cobalt spinel (NiCo2O4) was synthesized by the method of coprecipitation of the nickel and cobalt hydroxides with followed by drying (150 °C) and ultrasonic (US) treatment of the precipitate. The influence of US−treatment on the texture characteristics of the precursors and NiCo2O4 powders was established. The possibility of obtaining nanodispersed (crystallite size < 20 nm), mesoporous powders (pore size 3 − 15 nm) of nickel−cobalt spinel at a temperature of 700 °C is shown. The change in the specific electrical conductivity of sintered NiCo2O4 samples in the temperature range of 100 – 800 °C was studied, the value of σ can vary from 0.1 to 7.0 Sm/cm.

On the synthesis of bi-magnetic manganese ferrite-based core-shell nanoparticles.

Multifunctional nano-heterostructures (NHSs) with controlled morphology are cardinal in many applications, but the understanding of the nanoscale colloidal chemistry is yet to be fulfilled. The stability of the involved crystalline phases in different solvents at mid- and high-temperatures and reaction kinetics considerably affect the nucleation and growth of the materials and their final architecture. The formation mechanism of manganese ferrite-based core–shell NHSs is herein investigated. The effects of the core size (8, 10, and 11 nm), the shell nature (cobalt ferrite and spinel iron oxide) and the polarity of the solvent (toluene and octanol) on the dissolution phenomena of manganese ferrite are also studied. Noteworthily, the combined use of bulk (powder X-ray diffraction, 57Fe Mössbauer spectroscopy, and DC magnetometry) and nanoscale techniques (HRTEM and STEM-EDX) provides new insights into the manganese ferrite dissolution phenomena, the colloidal stability in an organic environment, and the critical size below which dissolution is complete. Moreover, the dissolved manganese and iron ions react further, leading to an inverted core–shell in the mother liquor solution, paving the way to novel synthetic pathways in nanocrystal design. The MnFe2O4@CoFe2O4 core–shell heterostructures were also employed as heat mediators, exploiting the magnetic coupling between a hard (CoFe2O4) and a soft phase (MnFe2O4).

In situ synthesis of oxidized MXene-based metal cobalt spinel nanocomposites for an excellent promotion in thermal decomposition of ammonium perchlorate

Oxidized MXene-supported MCo2O4 (oxidized MXene/MCo2O4, M = Mn, Zn, Cu and Co) nanocomposites with an excellent catalytic performance for AP decomposition were successfully synthesized through a facile hydrothermal assisted calcination method.

Structural, optical and morphological properties of zinc -doped cobalt-ferrites CoFe2−xZnxO4 (x=0.1-0.5)

Cobalt-ferrite (CoFe2O4) based nanoparticles are appropriate candidates for electrical, optical, and magnetic applications for electrical appliances. In the current study, a coprecipitation technique was used to prepare Zinc doped cobalt ferrites with compositions CoFe2−xZnxO4 (x=0.1-0.5) at various percentages using Zinc and Co-nitrate as precursors. The analysis of crystal phase structure, hkl planes, average crystalline size, volume, and lattice parameters of the unit cell of CoFe2-xZnxO4 doped (NPs) was carried under X-ray diffraction (XRD). X-ray spectra analysis, FT-IR Spectra, UV Visible Spectra, and SEM studies shown that the as-synthesized powders were contained of nano-crystallite size (42– 53nm) cubic-spinel phase with irregularly-structure. Calcination at low temperature (80˚C) of the precursor followed through sintering (500°C for 3h) con-sequence in a single-phase cubic-spinel shape with an average particle size of 42-53nm, as shown by scanning electron micrographs images. Sharp peaks and intense diff raction features in XRD pattern show that an increase in Zn doping concentration in cobalt spinel ferrite increases the crystalline behavior of the cubical spine phase. In cubical structure ferrites crystal lattices, the absorption band at low frequency is noticed above 400cm-1 but in the range of 300- 600cm-1 of the Fourier Transform Infrared bands were attributed to the tremblant of the ions of metal. The absorbance results of UV Spectra indicate that Zinc doped Cobalt Ferrite specimen had symbolic absorbance in the range of 660-900nm wavelength range of the conspicuous region. The Zn-doped cobalt-ferrite have a high strain derivative that could be a prospective material for electrical devices.

On the structure-property relationships of (Al, Ga, In)-doped spinel cobalt ferrite compounds: a combined experimental and DFT study.

We report a combined experimental and theoretical study of pure and doped cobalt ferrite where 25% of Fe3+ ions were replaced by Al3+, Ga3+, and In3+ ions, respectively, i.e., CoFe1.5X0.5O4 (X = Al, Ga, and In). The ferrite compositions were successfully synthesized using the solid-state reaction method. The X-ray powder diffraction method established that all ferrite samples had a spinel unit cell structure with the Fd3[combining macron]m (No. 227) space group. The lattice constants of ferrites increased from 8.382 Å (for undoped CoFe2O4) to 8.520 Å (for In-doped cobalt ferrite) in direct relation to the dopant ion size. The magnetic properties were obtained at 4.3 K and 300 K. At 4.3 K, the In-doped CoFe2O4 showed the highest saturation magnetic moment of 4.68 μB f.u.-1, while Al-doped CoFe2O4 showed the smallest value of 2.72 μB f.u.-1. The Fe3+ distribution among the spinel tetrahedral and octahedral sites was determined from the Mössbauer spectra. From ultraviolet-visible diffuse reflectance spectroscopy the direct optical bandgaps were determined, which have values between 1.20 eV and 1.28 eV for these ferrites. The ferrite compositions were also studied theoretically using plane-wave density functional theory using the CASTEP code where it was revealed that arrangements of the non-magnetic cations at the tetrahedral and octahedral sites strongly influence the electronic structure, the bandgap value, and the net magnetic moment per formula unit. Light Al3+ ions at the octahedral site give a low value of the net magnetic moment while the heavier Ga3+ and In3+ ions at the tetrahedral sites of the spinel give an enhanced magnetic moment. The magnetic moment values obtained from theoretical calculations match very well with the experimental values. Moreover, the theoretical calculations reveal that there exists a strong p-d hybridization among the oxygen and magnetic ions, which is affected by the non-magnetic dopant ions. The change in hybridization with the non-magnetic ion doping is responsible for the altered magnetic moments of the doped ferrites. Thus, our study provides a comprehensive investigation covering the synthesis and characterization of ferrites along with a good understanding of the phenomenon of how non-magnetic ion doping into spinel ferrites provides a method to tune the electronic and magnetic properties of the spinel ferrite.

Effects of Coloration of Spinel Cobalt Blue Pigments: Composition, Structure, and Cation Distribution

Effects of Coloration of Spinel Cobalt Blue Pigments: Composition, Structure, and Cation Distribution

Enhanced urea oxidization electrocatalysis on spinel cobalt oxide nanowires via on-site electrochemical defect engineering

A reversed-potential tuning strategy is proposed to introduce defects on the surface of cobalt oxide nanowires, enabling significantly improved electrocatalytic performance for urea oxidization under alkaline conditions.

First-principles study of antiferromagnetic cobalt spinels

We report a comparative study of the electronic structure and magnetic properties of two cobalt compounds Co3O4 and Co3S4, through first-principles Hubbard-U calculations. Our results indicate that Co3O4 and Co3S4 have similarities in crystal structure (normal spinel), magnetic order (antiferromagnetism), Co spin configuration (high spin Co2+ and low spin Co3+), and comparable band-gap energy. However, the U-dependence on electronic structure in two materials are different from each other. With a change in the applied U values, the band dispersion and the type of band gap are significantly changed in Co3O4, while the band-gap energy only is affected in Co3S4.

Green nanoceramic pigments based on cobalt chromite doped with Al: Synthesis, characterisation and colour performance

Nano-sized spinel cobalt chromite oxide CoCr2O4 and its substituted forms CoCr2−xAlxO4 (0 ≤ x ≤ 2) have been successfully synthesised by wet chemical route. The prepared powders were characterised by means of thermal analysis (DTA/TGA), X-ray diffraction (XRD), Field emission scanning electron microscopy (FE-SEM), Brunauer–Emmett–Teller analysis (BET), UV–visible techniques (UV–Vis) and colorimetric analyses (L* a* b*). The results show that the CoCr2−xAlxO4 (0 ≤ x ≤ 2) samples are in the crystalline phase at 900 °C with a particle size range of 20–200 nm. The colouration of the synthesised pigments is sensitive to the distribution of doping trivalent ions in the spinel lattice. The Al-enrichment leads to a colour shift from green to blue and the grains become more and more spherical and less agglomerated. Green cobalt chromite powders were substituted with 50% aluminium (CoCrAlO4), allowing the specific surface area of green nanometric powders to be increased from 7.4 to 12.4 m2/g.

Effect of rosemary extract on the microstructure, phase evolution, and magnetic behavior of cobalt ferrite nanoparticles and its application on anti-cancer drug delivery

Cobalt ferrite nanoparticles (CFO NPs) were synthesized by a modified sol-gel method using Fe(NO3)3.9 H2O and Co(NO3)2·6H2O as the sources of Fe 3+ and Co 2+ in presence of different volumes of rosemary extract and sucrose as gel agent, chelating agent and non-magnetic elements such as calcium and magnesium ions. The prepared nanoparticles were characterized via X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FT-IR), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The X-ray diffraction results confirmed that the sample prepared with 5 mL rosemary extract has single-phase spinel cobalt ferrite nanoparticles with a cubic crystal structure at 750 °C for 3 h (S1 sample). The average crystallite size was calculated about 33 nm using the Debye–Scherrer equation. Scanning electron microscopy also exposed that the prepared nanoparticles have a cubic morphology. Besides, the magnetic properties of the as-synthesized nanoparticles (S1 sample) indicated the highest saturated magnetization of 64 emu.g−1 as compared to other samples. The nanoparticles were then coated with tripolyphosphate (TPP) and chitosan polymer (Cs) to be applied as a carrier for drug delivery CoFe2O4-TPP-Cs (CFO-TPP-CS). The antioxidant doxorubicin (DOX) drug was then covered on the surface of the nanoparticles, and its drug release (CFO-TPP–CS–DOX) from the substrate of coated nanoparticles containing doxorubicin was evaluated at different pH levels. The coated CFO nanoparticles with tripolyphosphate (TPP) –Chitosan (Cs) sample indicated the biocompatibility and non-toxic nature of CFO-TPP- Cs NPs. Meanwhile, the CFO-TPP–CS–DOX nanosystem showed good death percentage of the breast cell cancer line (MCF-7 cell) in an acidic medium.

Correction to “Spontaneous Delithiation under Operando Condition Triggers Formation of an Amorphous Active Layer in Spinel Cobalt Oxides Electrocatalyst toward Oxygen Evolution”

Correction to “Spontaneous Delithiation under Operando Condition Triggers Formation of an Amorphous Active Layer in Spinel Cobalt Oxides Electrocatalyst toward Oxygen Evolution”

Synthesis of Mesoporous NiCo2O4 By Spray Pyrolysis Method for Air Electrode of Zinc-Air Rechargeable Batteries

Recently, rechargeable zinc-air batteries have been attracted attention as promising energy storage devices because of their theoretical large capacity, low cost, and safety. However zinc-air battery still has limits in cycle file and energy efficiency. In particular, increase in air electrode performance is strongly required. Therefore, variety of materials, mainly perovskite oxide, have been studied for air electrode, however, activity and stability are still not high enough. In this study, nickel cobalt spinel oxide was synthesized by spray pyrolysis method in order to increase in surface area and formation of mesoporous structure. In our previous study, it was found that introduction of mesoporous structure in LaCoO3 electrode with hard template method is effective for increasing cycle performance and decrease in overpotential of air electrode for zinc-air battery. NiCo2O4 based spinel oxide is active to oxygen reduction (ORR) and oxygen evolution reaction (OER), however, surface area is still insufficient by the preparation of conventional hydrothermal method. Therefore, it is expected that introduction of mesoporous structure into NiCo2O4 spinel oxide will increase ORR/OER activity and stability.On spray pyrolysis method, precursor solvent turned into nano-sized droplet by ultrasonic wave vaporizer, and the droplets are transferred to the tubular electric furnaces by air as carrier gas. The solvent evaporates from the droplets resulting in the formation of mesopore and after calcination, the fine powder is gathered in filters. Nitrate solution was used as precursor, and air at 3 L/min was used as oxidant and carrier gas in this work. Air electrode performance was measured by using gas diffusion layer and PTFE and graphitic carbon was mixed with NiCo2O4 spinel for electrode. 8M KOH aqueous solution at 313K was used for electrode and constant current of 20 mA/cm2 was applied by battery charge discharge equipment.Single phase of NiCo2O4 spinel phase was obtained from XRD measurement and the SEM image of the sample was spherical with many meso size pore. The estimated BET surface area was 76m2/g and average pore diameter was 2.12 nm. Therefore, it is considered that NiCo2O4 oxide with mesoporous structure was successfully prepared. ORR/OER activity of mesoporous NiCo2O4 was measured. It was found that NiCo2O4 shows reasonable activity to ORR and OER reaction. On the other hand, partial substitution of Ni with Fe is effective for increasing ORR/OER activity. Two different compositions of iron added NiCo2O4 (Ni0.8Fe0.2Co2O4, Ni0.65Fe0.35Co2O4) are successfully prepared. At beginning of charge/discharge cycle, spray pyrolysis synthesized NiCo2O4 shows slightly larger overpotential for ORR and OER comparing with that of NiCo2O4 prepared with hydrothermal method. However, after some cycles, ORR potentials are increased and OER potentials are decreased, so mesoporous NiCo2O4 shows superior electrochemical performance which is almost the same with that of hydrothermal NiCo2O4. Moreover, cycle stability is much higher than that of hydrothermal NiCo2O4 and ORR/OER more than 500 cycles was stably sustained and so introduction of mesoporous structure is effective for increasing cycle stability of air electrode. Effects of calcination temperature during splay pyrolysis were also studied and it was found that calcination of NiCo2O4 based spinel oxide at 673 K is the most active and stable to ORR/OER. Therefore, this study reveals that Fe doped NiCo2O4 with mesoporous structure is highly active and stable air electrode catalyst for Zn-air battery.

Air Electrode Property of Doped NiCo2O4 Based Oxide for Rechargeable Zn-Air Battery

There is a strong demand for rechargeable battery with large energy density and capacity because of increase in performance of mobile equipment such as mobile phone, laptop personal computer (PC) and also electric vehicle. At present, Li ion battery (LIB) have been widely used for such purpose. However, there are several issues such as the insufficient capacity and safety required to solve. Zinc-air batteries have been used commercially as a non rechargeable battery at present, however, recently, there is strong interest for development of rechargeable Zn-air battery because of its theoretical large capacity, low cost, and safety. However zinc-air rechargeable battery still has limits in cycle file and energy efficiency. In particular, increase in air electrode performance is strongly required. In this study, nickel cobalt spinel oxide, NiCo2O4, was studied as reversible air electrode for Zn-air battery. In addition, effects of dopant on oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were studied. NiCo2O4 based spinel oxide is active to ORR and OER, however, surface area is still insufficient by the preparation of conventional hydrothermal method. Therefore, application of splay pyrolysis method for preparation of NiCo2O4 oxide is also studied for increasing ORR/OER activity and stability.NiCo2O4 based oxide was prepared by hydrothermal synthesis method and partial substitution was performed by using Mn, Fe, and Cu. On spray pyrolysis method, precursor solvent turned into nano-sized droplet by ultrasonic wave vaporizer, and the droplets are transferred to the tubular electric furnaces by air as carrier gas. The solvent evaporates from the droplets resulting in the formation of mesopore and after calcination, the fine powder is gathered in filters. Air electrode performance was measured by using gas diffusion layer, and PTFE and graphitic carbon were mixed with NiCo2O4 spinel for electrode. 8MKOH aqueous solution at 313K was used for electrolyte and a constant current of 20 mA/cm2 was applied by battery charge discharge equipment.Various spinel oxides were successfully prepared by hydrothermal synthesis method from XRD measurement. It was found that ORR and OER activity of MnCo2O4 and NiCo2O4 was reasonably high among the spinel oxides prepared. ORR activity is slightly higher on MnCo2O4, however, NiCo2O4 shows much longer cycle stability of ORR/OER. In addition, elution of Mn was observed in case of MnCo2O4, in contrast, almost no change in composition was observed for NiCo2O4 after cycle measurement. Therefore, NiCo2O4 shows reasonable activity to ORR and OER and high chemical stability. Effects of dopant on NiCo2O4 on ORR and OER activity and doping Cu and Fe is effective for increasing ORR potential and decreasing OER potential. Although the most superior performance of air electrode was observed on Cu doped one, elution of Cu is obviously observed. Therefore, from chemical stability, Fe doped NiCo2O4 is the most active to air electrode catalyst. The optimization of Fe amount in Ni site was also studied and it was found that Ni0.65Fe0.35Co2O4 is the most active and stable air electrode catalyst. On this electrode, overpotential for ORR reaction is around 0.25V at 20mA/cm2, 313 K and almost 500 cycles of ORR/OER which is 1 h ORR and OER each. In addition, introduction of mesoporous structure was achieved by splay pyrolysis method and increase in surface area is also effective for increasing stability to ORR/OER activity.This work is based on results obtained from a project, "Research and Development Initiative for Scientific Innovation of New Generation Batteries (RISING2)", JPNP16001, commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

Synthesis, structural, magnetic, textural, optical investigation and photocatalytic performance of undoped and doped cobaltite nanoparticles

The present work deals with the synthesis and characterization of pure and transition metal (Ni, Cu and Fe) doped spinel Co3O4 nanoparticles (NPs), which are well known for their physical and chemical features. These transition metal doped Co3O4 NPs were tailored through thermal decomposition of precursors synthesized by simple co-precipitation, the simple and cost-effective strategy of fabricating mesoporous spinel cobalt oxide. This study investigates the photocatalytic degradation of industrial dyes Rhodamine B (RhB) and Methyl Orange (MO) under sunlight by using NPs as catalysts. Among the different nanocatalysts, Ni doped Co3O4 NP exhibited the highest efficiency in degrading the environmentally harmful dyes, proving the positive correlation between surface area and photodegradation efficiency. The structures and optical properties were investigated by Powder X-Ray Diffraction (PXRD), X-ray Photoelectron Spectroscopy (XPS), High-Resolution Transmission Electron Microscopy (HR-TEM), Ultraviolet-Diffuse Reflectance Spectroscopy (UV-DRS) and Photoluminescence (PL) under dopant control. The morphology and polycrystallinity of the samples were studied using SEM-EDS and SAED patterns, respectively. The doped ferromagnetic samples showed unsaturation in hysteresis loops which specified the oxygen vacancy.

Bioethanol Steam Reforming over Cobalt-Containing USY and ZSM-5 Commercial Zeolite Catalysts

The ethanol steam reforming process (ESR) over cobalt-based zeolitic catalysts, differing significantly in the structure, was comprehensively examined. The cobalt spinel phase (10wt%) was deposited on the surface of USY and ZSM-5 zeolites (Si/Al ratio of 31). The catalysts were characterized in terms of their chemical (ICP) and phase composition (XRD), textural properties (low-temperature N2 adsorption), morphology (STEM/EDX), and reducibility (H2-TPR). The aforementioned characteristics were supplemented by the catalysts’ acidity and redox properties investigations (quantitative FT-IR studies of pyridine and carbon monoxide adsorption). Catalysts' activity was evaluated in the ESR process at 500C for various ethanol/water mixtures. Both catalysts exhibited 100% ethanol conversion, whereas their selectivity towards H2, CO2, and C2H4 strongly depended on the applied ethanol to water molar ratio. Comparable selectivities observed for the 1:4 ratio were improved for the 1:9 ratio for both catalysts, as expected. For the ratio of 1:12, the significant difference in the reaction paths (the ethanol dehydration for CoUSY and the ethanol steam reforming for CoZSM-5) was explained by the cobalt reoxidation process facilitated by water molecules for the CoUSY. The superior overall performance of the CoZSM-5 catalyst in the ESR process, in comparison to CoUSY, also results from its almost three times enhanced accessibility of the cobalt species, as confirmed by the quantitative FT-IR studies of CO sorption. The microscopic studies also indicated a better dispersion of the cobalt phase supported on the ZSM-5 support. Thus, the structure of ZSM-5 zeolite assures higher cobalt active phase dispersion being more beneficial for the ESR process.

Cobalt ferrite microspheres as a biocompatible anode for higher power generation in microbial fuel cells

In the present study, spinel cobalt ferrite hierarchical flower-like microspheres (CoFe2O4-MS) are fabricated using a hydrothermal method and utilized as a biocompatible anode in microbial fuel cells (MFCs) for power generation. A maximum power density of 1964 mW m−2 is achieved with CoFe2O4-MS in a mediator-less MFC using Escherichia coli as a biocatalyst and glucose as a fuel. The unprecedented power generation by CoFe2O4-MS can be attributed to (i) the morphology of the flower-like CoFe2O4-MS, with a rough surface and large surface area suitable for biofilm formation, (ii) the rapid immobilization of negatively charged E. coli cells on the positively charged CoFe2O4-MS, facilitating stronger bacterial adhesion between the bacterial cells and CoFe2O4-MS, which leads to lower contact resistance and advantageous interfacial properties with rapid electron transfer, and, more importantly, (iii) enhanced interfacial charge transfer due to the presence of multi-valent cations and multiple valence states in the highly electrocapacitive CoFe2O4-MS. Thus, the enrichment of electroactive E. coli on CoFe2O4-MS produces a large number of electron-shuttling endogenous redox mediators, which promotes efficient extracellular electron transfer between E. coli and the electrocapacitive CoFe2O4-MS during the oxidation of the substrate, thus generating higher power output.

Hydrothermal Synthesis of Euhedral Co3O4 Nanocrystals via Nutrient-Assisted Topotactic Transformation of the Layered Co(OH)2 Precursor under Anoxic Conditions: Insights into Intricate Routes Leading to Spinel Phase Development and Shape Perfection

Euhedral cobalt spinel cubes, octahedra, and cuboctahedra with narrow size dispersions have been synthesized in a one-pot hydrothermal reaction, using cobalt(II) nitrate and sodium hydroxide at variable concentrations as the only reagents, while their ratio was kept constant at cCo2+/cOH– = 2.7. Three main reaction stages, including parent reactive template (PRT) formation, nutrient-mediated topotactic nucleation (NTN), and morphogenesis of nanocrystals (MNC), were distinguished. In the NTN step, the primary spinel grains development occurs with the [100] and [111] directions of the Co3O4 facets inheriting the [1–11] direction of the elongated PRT plates (formation of cubes) or the [001] direction of the hexagonal PRT plates (formation of octahedra). In an anoxic environment, the excess nitrate anions play a critical role as the Co2+ to Co3+ oxidants and oxygen donors required to attain the Co3O4 stoichiometry. The nucleated Co3O4 primary nanocrystals are spontaneously assembled into sub-micrometer spinel mesocrystals via imperfectly oriented attachments and then consolidated into euhedral bulk nanocrystals by a hydrothermal treatment (nanocubes) or via dissolution and reentrant recrystallization processes (octahedra and cuboctahedra).

Structural, magnetic, and impedance properties of Co1-xZrxFe2O4 nanocrystallites by PEG-assisted sol-gel route

This work presents the Zr4+-substituted CoFe2O4 nanocrystallites at lower concentrations prepared via sol-gel method in order to investigate their structural and magnetic properties along with their impedance properties. XRD patterns confirm the inverse spinel phase of CoFe2O4 and the presence of zirconium (Zr) nanoparticles in the spinel network. The crystallite size was found to decrease after Zr substitution. CoFe2O4 nanocrystallites of 34-nm size and lattice parameter slightly increase with Zr4+ substitution into cobalt ferrite as observed from the XRD pattern. The presence of all functional groups involved in the present synthesis was determined from FTIR spectroscopy. Characteristic peaks of cubic spinel structured cobalt ferrites are observed in the Raman spectrum of each ferrite composition. The HRSEM images revealed the spherical morphology and nanosize of the Zr4+-doped CoFe2O4 nanocrystallites. EDX analysis confirmed that the applied process for the fabrication of Co1-xZrxFe2O4 nanoparticles is a proper process for the synthesis of spinel cobalt ferrites with homogeneity in composition. The TEM images evidently exposed formation of well-shaped nanoparticles and the fringes are uniform with 0.44-nm width and the selected area electron diffraction pattern exposed periodic arrangements. The results of magnetic hysteresis revealed that the zirconium-substituted cobalt ferrite nanoparticles increase the saturation magnetization and coercivity with increasing zirconium content. Impedance increased when Zr4+ was substituted, but for higher concentration it was reduced.

Detailed analysis of structural and optical properties of spinel cobalt doped magnesium zinc ferrites under different substitutions

Spinel ferrites nanoparticles have complex considerable interest in several technical applications because of their different magnetic behavior. These magnetic nanoparticles obtain finite size and surface effects. The Co doped Mg-Zn ferrites were prepared by co-precipitation method. The structural characterization of the samples was done for Mg0.5Zn0.5-xCoxFe2O4 (X = 0.01–0.05) nano ferrites using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV spectroscopy and Fourier transform infrared spectroscopy (FTIR). The cubical spinel structure of single phase has been obtained. As the concentration of Cobalt in the magnesium zinc ferrite increases, the crystallinity of the cubic spinel phase gradually increases. As increasing the concentration of Co+2 the lattice constant disorderly the lattice symmetry. Absorption spectra display a change in position of maximum absorption near the higher wavelength with increased Co2+ content. Some XRD parameters, using proposed X-ray morphology index, average crystalline size, lattice parameter, Density, Volume of unit cell, etc., have been evaluated. The absorption spectra reveal that in visible region Co-doped Mg-Zn ferrite close infrared region has low absorption rate moreover; in UV region the absorption is high. The evaluation of bandgap of Co-doped MgZnFe2O4 is the important features of its optical characteristics. The SEM image shows the non-uniform grains distributions for all compositions. The IR spectroscopy is a versatile tool for the identification of purity, functional groups, and phase of samples.