Ferrites Of Various Compositions Research Articles

Synthesis, structure, and visible-light-driven activity of o-YbFeO3/h-YbFeO3/CeO2 photocatalysts

Photo-Fenton-like oxidation of organic substances is one of the key advanced oxidation processes based on the reversible Fe2+↔Fe3+ transition and the generation of a strong oxidant ·OH in the presence of H2O2 and is currently considered as a promising method for the purification of polluted aqueous media. However, the absence of effective and stable photocatalysts of this process, operating under the action of visible light, necessitates the exploratory studies, mainly among iron oxides and ferrites of various compositions and structures. In this work, using the method of solution combustion followed by heat treatment in air the heterojunction nanocomposites based on ytterbium orthoferrite and cerium dioxide of the composition o-YbFeO3/h-YbFeO3/CeO2 (0–20 mol.%) with high absorption in the visible region and advanced photo-Fenton-like activity were obtained. The nanocomposites were studied by EDS, SEM, XRD, BET, and DRS methods. The photo-Fenton-like activity of the nanocomposites was investigated during the degradation of methyl violet under the action of visible (λmax = 410 nm) radiation. As a result, the formation of I-type heterojunction based on stable rhombic (55.4–79.0 nm) and metastable hexagonal (19.5–24.0 nm) modifications of ytterbium orthoferrite (o-YbFeO3 and h-YbFeO3, respectively) and cubic cerium dioxide CeO2 (13.2–19.2 nm) nanocrystals was established. It was shown that the obtained nanocomposites had foamy morphology and were characterized by a specific surface in the range of 9.1–25.0 m2/g, depending on the CeO2 content. It was found that nanocrystalline components were chemically and phase-pure, uniformly spatially distributed over the nanocomposite, and had multiple contacts with each other. Based on this fact and the established electronic structure of the nanocomposite components, the formation of I-type heterojunction with the participation of o-YbFeO3 (Eg = 2.15 eV), h-YbFeO3 (Eg = 2.08 eV), and CeO2 (Eg = 2.38 eV) was shown, the presence of which increased photocatalytic activity of the resulting nanocomposite. The optimal content of CeO2 in the nanocomposite was 5%, and the o-YbFeO3/h-YbFeO3/CeO2–5% sample was characterized by the highest rate constant of photo-Fenton-like degradation of methyl violet under the action of visible light equal to k = 0.138 min–1, which was 2.5 to 5 times higher than for nanocomposites based on ytterbium orthoferrite. The obtained results obtained indicate that the developed nanocomposites can be considered as a promising basis for the advanced oxidation processes for the purification of aqueous media from organic pollutants.

The effects of cobalt and magnesium co-doping on the structural and magnetic properties of ZnFe2O4 synthesized using a sonochemical process

In this study, Zn1-xCo0.5xMg0.5xFe2O4 ferrites of various compositions were synthesized using a sonochemical approach. X-ray diffraction tests on the samples revealed the formation of pure spinel ferrite with a cubic structure. The lattice constant, X-ray density, and cation distribution were all affected by cobalt and magnesium doping. Tolerance factor is very close to unity, it suggests a very stable spinel ferrite structure. The cation distribution implies that the compounds are partially inverse spinels or mixed spinels. The FTIR analysis confirms the tetrahedral and octahedral positions of the M − O bond. When Co2+ - Mg2+ is doped in zinc ferrite, the morphological transition occurs, according to morphological investigations. The elemental composition of as-synthesized ferrite was confirmed by using EDS analysis. A Vibrating Sample Magnetometer (VSM) was used to examine the magnetization of ferrite at ambient temperature, and the ferrite changed from superparamagnetic to ferromagnetic when the concentration of Co2+ and Mg2+ ions increased.

Профильный анализ пленок ферритов-гранатов методом оптической эмиссионной спектроскопии тлеющего разряда

Annotation.The paper presents the results of experiments on the application of the method of optical emission spectroscopy of a glow discharge for the profile analysis of vacuum-deposited single and two-layer films of multicomponent garnet ferrites of various compositions before and after crystallization annealing. The presence of internal and external transition layers was revealed, and the modification of their elemental composition during crystallization, as well as the different sequence of synthesis of individual components in ferrite-garnet heterostructures, was investigated.

Estimation of structural composition of the inverse spinel ferrites using 57Fe-Zero Field Nuclear Magnetic Resonance

We have demonstrated 57Fe Zero Field Nuclear Magnetic Resonance (ZFNMR) as a powerful tool in determining the structural composition of nickel-cadmium spinel ferrites of various compositions of Ni1-x Cdx Fe2O4 from x = 0 to1, which are synthesized via one-step auto combustion technique. The XRD measurements confirm the phase purity of all the samples. Vibrating Sample Magnetometry (VSM) measurements show that saturation magnetization (MS) increases initially (up to x = 0.3) and then decreases for higher concentrations of cadmium. The Fe3+ ions in the inverted spinel ferrite distribute equally among two possible sites (tetrahedral A and octahedral B) with different hyperfine fields. Therefore for x = 0 under the assumption that Ni enters B sites, 57Fe NMR of Fe3+ ions yield two signals of equal integral intensities in spectral lines corresponding to these sites. Thus, for the sample series Ni1-x Cdx Fe2O4, the contribution of Fe3+ nuclei varies for A and B sub-spectra with the substitution of a non-magnetic Cd2+ ion. By measuring the Fe3+ distribution on A and B sites which is determined from relative spectral areas of A and B NMR sub-spectra the cation distribution is estimated and has been verified by the binomial distribution. Further, XRD Rietveld refinement results are also in good agreement with the composition estimated by NMR technique and the ideal composition. We have demonstrated the usefulness of NMR technique to quantify the accurate composition of the mixed spinel ferrite systems using Ni-Cd ferrite as a test case. Further, the estimated inversion parameter (at around x = 0.4), for the studied system, obtained from ZFNMR, XRD, and VSM techniques are in excellent agreement with each other.

A Novel and Simple Process for Nanosized Mg‐Mn Ferrite Preparation from Solution Combustion Method and Study of its Characteristics

A novel solution combustion method has been used to prepare Mg‐Mn ferrites of various compositions, Mg0.9Mn0.1Fe1‐xO4 where x = 0.2, 0.4, 0.6, 0.8, and the properties were investigated in the present work. Nano‐size Mg‐Mn ferrite particles with diameter in the range of 8~ 15 nm were successfully formed via this method. The combustion temperature of the oxidation‐reduction was apparently occurred at 200°C. The result of X‐ray diffraction (XRD) analysis indicated that the as‐burnt powder affords a pure single spinel ferrite phase at low temperature. The thermal analysis of nitrate–citrate gels was characterized by DTA‐TG. The TEM and SEM observations give the morphology and microstructure of the products. The dielectric properties of the sintered Mg‐Mn ferrites were investigated by using HP/Agilent 4291B RF impedence/material analyzer. It was found that there was no maximum dielectric loss within the measured frequency range until 1 GHz due to excellent compositional control in this method.

Thermoelectric Power Studies Cu-Cd Ferrites

Thermoelectric Power Studies of Cadmium Substituted Copper Ferrites of various compositions were investigated from room temperature to well beyond the curie temperature by differential method. The Seebeck coefficient is negative for all compositions showing that these ferrites behave as n-type semi conductors. Plots of Seebeck coefficient verses tem- perature shows maximum at Curie temperature. On the basis of these results an explanation for the conduction mechanism in Cu-Cd mixed ferrites is suggested.

Thermoelectric power studies of Cu–Co ferrites

Thermoelectric power studies of cobalt substituted copper ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. Plot of Seebeck coefficient versus temperature show a maximum at Curie temperature. On the bases of these results an explanation for the conduction mechanism in Cu–Co mixed ferrites is suggested.

Thermoelectric power studies of La 3+ substituted strontium hexagonal ferrites

Thermoelectric power studies of La 3+ substituted strontium hexagonal ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. Plots of Seebeck coefficient versus temperature are shown to be maximum at Curie temperature. On the basis of these results an explanation for the conduction mechanism in La–Sr ferrites is suggested.

Thermoelectric power studies of magnesium and aluminium substituted lithium ferrites

Thermoelectric power studies of Mg and Al substituted Li ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The temperature variation of the Seebeck coefficient is also discussed. On the basis of these results, an explanation for the conduction mechanism in Mg–Al–Li mixed ferrites is suggested.

High temperature thermoelectric power studies of Cu–Cr ferrites

Thermoelectric power studies of Cu–Cr ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. Plots of the Seebeck coefficient versus temperature show a maximum at Curie temperature. On the basis of these results, an explanation for the conduction mechanism in Cu–Cr mixed ferrites is suggested.

Processing of Nickel–Zinc Ferrites Via the Citrate Precursor Route for High‐Frequency Applications

Nickel–zinc ferrites of various compositions, Ni1−xZnxFe2O4wherex=0.2, 0.4, 0.5, and 0.6 investigated in the present work, have been prepared by the citrate precursor method. The complex permittivity (∈′−j∈″) and permeability (μ′−jμ″) of the ferrites were measured at X‐band (8–12 GHz) microwave frequencies. The dielectric constants or the real part of permittivity, ∈′, are observed to lie in the range 5.46–8.95 for ferrites sintered at 1200°C, while those sintered at 1300°C exhibit relatively higher dielectric constants. The permittivity loss, tan δ∈(=∈″/∈′), is observed to be of the order of 10−2–10−3, depending upon the composition and sintering temperature of the ferrite. These losses are lower by at least one to two orders of magnitude compared with those normally reported for ferrites processed by the conventional ceramic method. The presently studied ferrites also exhibit high values of DC‐resistivity, 107–1011Ω·cm. The low dielectric losses and high resistivity can be co related to small grain size and better compositional stoichiometry obtained as a result of processing via the citrate route. Magnetic properties such as the Curie temperature, saturation magnetization, initial permeability, andB–Hhysteresis parameters of the compositions withx=0.5 and 0.6 are also given.

Electrical Conductivity of Chromium Substituted Copper Ferrites.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Thermoelectric power studies of Ca–Co ferrites

Thermoelectric power studies of cobalt substituted calcium ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. Plots of the Seebeck coefficient versus temperature show a maximum at Curie temperature. On the basis of these results an explanation for the conduction mechanism in Ca–Co mixed ferrites is suggested.

Thermoelectric power studies of La–Co substituted Sr M-type hexagonal ferrites

Thermoelectric power studies of Sr–La–Co hexagonal ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The values of the charge carrier concentration have been computed from the observed values of the Seebeck coefficient. On the basis of these results an explanation for the conduction mechanism in Sr–La–Co mixed ferrites is suggested.

High temperature thermoelectric power studies of cobalt and titanium substituted barium hexagonal ferrites

Thermoelectric power studies of cobalt and titanium substituted barium hexagonal ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck Coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. Plots of Seebeck coefficient vs. temperature show a maximum at Curie temperature. On the basis of these results an explanation for the conduction mechanism in Ba–Co–Ti mixed ferrites is suggested.

Thermoelectric power studies of Co–Ge ferrites

Thermoelectric power studies of Co–Ge ferrites of various compositions were made from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The values of the charge carrier concentration have been computed from the observed values of the Seebeck coefficient. The temperature variation of the Seebeck coefficient is also discussed. On the basis of these results an explanation for the conduction mechanism in Co–Ge mixed ferrites is suggested.

Room temperature electric properties of cadmium-substituted nickel ferrites

Electric properties such as electrical conductivity and thermoelectric power studies of Ni–Cd ferrites of various compositions were investigated at room temperature. The Seebeck coefficient is negative for all the ferrites, showing that these ferrites behave as n-type semiconductors. On the basis of these results, an explanation for the conduction mechanism in Ni–Cd mixed ferrites is suggested.

Thermoelectric power studies of polycrystalline magnesium substituted lithium ferrites

Thermoelectric power studies of Li–Mg ferrites of various compositions were investigated from room temperature to well beyond the Curie temperature by the differential method. The Seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The values of the charge carrier concentration have been computed from the observed values of the Seebeck coefficient. On the basis of these results an explanation for the conduction mechanism in Li–Mg mixed ferrites is suggested.

Dielectric properties of Li–Ge ferrites

Dielectric properties such as dielectric constant ( ε′) and dielectric loss tangent (tan δ) of Li–Ge ferrites of various compositions have been measured in high frequency from 1 to 13 MHz using HP 4192 A impedance analyser. Plots of dielectric constant ( ε′) versus frequency show a normal dielectric of spinel ferrites. The frequency dependence of dielectric loss tangent (tan δ) is found to be abnormal and giving a peak at 10-MHz frequency. A qualitative explanation is given for the composition and frequency dependence of dielectric constant and dielectric loss tangent.

Electrical transport properties of erbium substituted Ni–Zn ferrites

Electrical transport properties such as electrical conductivity (σ) and thermoelectric power (S) of erbium substituted Ni–Zn ferrites of various compositions have been investigated from room temperature to well beyond the Curie temperature. Plots of log (σT) versus 103/T are linear and show a transition near the Curie temperature. On the basis of Seebeck coefficient (S), the ferrites under investigation have been classified as n type semiconductors. The activation energy in the ferrimagnetic region is in general less than that in the paramagnetic region. An attempt is made to explain the conduction mechanism in these ferrites. The properties of gadolinium substituted Ni–Zn ferrites have been correlated with these of erbium substituted Ni–Zn ferrites.