Strontium Ferrite Research Articles

Removal of Fluoride in Water Using Sustainable Strontium Ferrite Graphene Nano Composite

Removal of Fluoride in Water Using Sustainable Strontium Ferrite Graphene Nano Composite

Triggering electrode multi-catalytic activity for reversible symmetric solid oxide cells by Pt-doping lanthanum strontium ferrite

Among the up-and-coming technologies, reversible solid oxide cells (r-SOCs) represent a highly efficient way to store and convert energy using a single device. The interchangeability between SOFC and SOEC operation is the key aspect, though for its technological advancement the development of performing, versatile and robust electrodes must be pursued. A multi-purpose catalyst would allow for the design of a reversible symmetric cell (r-SSOC), greatly reducing fabrication and maintenance costs. However, such a flexible electrode material must comply with the requirements of both SOC electrodes, namely ensuring high performance in a wide pO2 range: catalytic activity towards fuel oxidation and H2O/CO2 reduction, electronic and ionic conductivity, long-term stability, tolerance to carbon deposition. In this work, platinum doping at the B-site of a lanthanum strontium ferrite (LSFPt) endowed the parent perovskite with superior versatility, making it able to operate as oxygen exchange catalyst as well as fuel electrode material. 5-mol% Pt inclusion enhanced the ORR/OER activity, lowering the LSF area-specific resistance by 29% and approaching the state-of-the-art LSCF performance. After reduction, Pt-Fe finely distributed exsolution provided the fuel electrode with catalytically active sites. LSFPt-symmetric H2-SOFCs and CO2-SOECs, displayed 720 mW∙cm−2 power density and 1.66 A·cm−2 current density at 1.6 V, respectively, at 850 °C. Endurance tests on LSFPt-based r-SSOCs demonstrated a remarkably stable SOFC/SOEC cyclability and a steady current density output for over 370 h in 50:50 CO2:CO at 850 °C.

Kinetic and Thermodynamic Enhancement of Low-Temperature Oxygen Release from Strontium Ferrite Perovskites Modified with Ag and CeO2.

The redox behavior of the nonstoichiometric perovskite oxide SrFeO3-δ modified with Ag, CeO2, and Ce was assessed for chemical looping air separation (CLAS) via thermogravimetric analysis and by cyclic release and uptake of O2 in a packed bed reactor. The results demonstrated that the addition of ∼15 wt % Ag at the surface of SrFeO3-δ lowers the temperature of oxygen release in N2 by ∼60 °C (i.e., from 370 °C for bare SrFeO3-δ to 310 °C) and more than triples the amount of oxygen released per CLAS cycle at 500 °C. Impregnation of SrFeO3-δ with Ag increased the concentration of oxygen vacancies at equilibrium, lowering (3 - δ) under all investigated oxygen partial pressures. The addition of CeO2 at the surface or into the bulk of SrFeO3-δ resulted in more modest changes, with a decrease in temperature for O2 release of 20-25 °C as compared to SrFeO3-δ and a moderate increase in oxygen yield per reduction cycle. The apparent kinetic parameters for reduction of SrFeO3-δ, with Ag and CeO2 additives, were determined from the CLAS experiments in a packed bed reactor, giving activation energies and pre-exponential factors of Ea,reduction = 66.3 kJ mol-1 and Areduction = 152 mol s-1 m-3 Pa-1 for SrFeO3-δ impregnated with 10.7 wt % CeO2, 75.7 kJ mol-1 and 623 molO2 s-1 m -3 Pa-1 for SrFeO3-δ mixed with 2.5 wt % CeO2 in the bulk, 29.9 kJ mol-1 and 0.88 molO2 s-1 m-3 Pa-1 for Sr0.95Ce0.05FeO3-δ, and 69.0 kJ mol-1 and 278 molO2 s-1 m-3 Pa-1 for SrFeO3-δ impregnated with 12.7 wt % Ag, respectively. Kinetics for reoxidation were much faster and were assessed for two materials with the slowest oxygen uptake, SrFeO3-δ, giving the activation energy Ea,oxidation = 177.1 kJ mol-1 and pre-exponential factor Aoxidation = 3.40 × 1010 molO2 s-1 m-3 Pa-1, and Sr0.95Ce0.05FeO3-δ, giving the activation energy Ea,oxidation = 64.0 kJ mol-1, and pre-exponential factor Aoxidation = 584 molO2 s-1 m-3 Pa-1.

Effects of calcination temperatures on structural, functional, morphological, and magnetic properties of strontium ferrite (SrFe2O4) nanoparticles

In this proposed work, the strontium ferrite (SrFe2O4) nanoparticles were successfully synthesized in the presence of strontium nitrate (Sr (NO3)2) and ferric nitrate (Fe (NO3).9H2O) as primary sources by using chemical co-precipitation method. The prepared powders were kept different calcinations temperature (650, 750 and 850 ​°C) and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM) techniques. The XRD patterns demonstrated the cubic and orthorhombic phase of spinel formation and FTIR transmittance spectra confirmed the presence of strontium ferrite related molecular functional groups. Further, SEM micrograph showed spherical nanoparticles with less agglomerated structure. VSM studies revealed the hard magnetic properties with the highest saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc) of 22.17 emu/g, 11.807 emu/g and 5662.6 ​Oe respectively by VSM.

Structural and magnetic properties of BaFe9.95Al2Mg0.05O19 tuned through sintering temperature

The sintering temperature is a key way to tune the structural and magnetic properties of M-type hexaferrites. Here the effect of BaFe9.95Al2Mg0.05O19 M-type hexagonal Ba-hexaferrites, was studied. X-ray diffraction analysis revealed the presence of Fe2O3 impurity phases in all samples. The results showed that as the sintering temperature increased, the saturation magnetization (Ms) and remanence ratio (Mr/Ms) initially increased, then decreased at higher temperatures. On the other hand, the coercivity (Hc) and magnetocrystalline anisotropy field (Ha) decreased first, then increased. The average grain size (D) consistently grew between 800–2800 nm with increase in pre-sintering temperature. The optimal magnetic properties of BaFe9.95Al2Mg0.05O19 were achieved at a pre-sintering temperature of 1280 °C, with Ms = 49.94 emu g−1, Hc = 4.99 kOe, Ha = 1.5 kOe, and mB = 9.4097 μB. The findings suggest that magnetic properties of M-type hexagonal strontium ferrite can be significantly enhanced by optimizing the pre-sintering temperature, which has implications for the development of high-performance self-biased circulators, Magnetic filters and other magnetic applications.

Synthesis, Structural Properties, and Resistance to High-Temperature Degradation of Perovskite Ceramics Based on Lanthanum–Strontium Ferrite

This work is dedicated to the study of the properties of perovskite ceramics based on lanthanum–strontium ferrite, and to the evaluation of their resistance to long-term thermal aging. As a method for obtaining perovskite ceramics, the method of solid-phase mechanochemical grinding and consequent thermal annealing of the resulting mixtures was chosen. The novelty of the study consists in the assessment of the phase transformation dynamics in lanthanum–strontium ferrite-based ceramics in relation to the annealing temperature, alongside the study of the effect of the phase composition of ceramics on the resistance to high-temperature aging, which is characteristic of the operating modes of these ceramics as materials for solid oxide fuel cells. To study the properties, the methods of scanning electron microscopy, energy dispersive analysis, and scanning electron microscopy were applied. Pursuant to the outcome of elemental analysis, it was established that no impurity inclusions appear in the ceramic structure during the synthesis, and a growth in the annealing temperature results into a decline in the grain size and a growth in their density. During the analysis of the acquired X-ray diffraction patterns, it was found that a growth in the annealing temperature above 500 °C results in phase transformations of the LaFeO3/SrFe2O4 → La0.3Sr0.7FeO3/LaSr2FeO8/La3FeO6 type, followed by structural ordering and a decline in deformation distortions with a growth in the annealing temperature. An analysis of the conductive properties of ceramics has established that the dominance of the La0.3Sr0.7FeO3 phase in the structure results in a growth in conductivity and a decline in resistance. Life tests for degradation resistance have shown that for three-phase ceramics, the rate of degradation and amorphization is significantly lower than for two-phase ceramics.

Pt-Doped Lanthanum Ferrites as Versatile Electrode Material for Solid Oxide Cells

The tailoring of multi-tasking perovskite oxide-based electrodes for solid oxide cells has shown growing interest. The development of flexible structures represents a crucial step towards the design of symmetric and possibly SOFC/SOEC reversible systems. In this work, low (0.5 mol%) B-site Pt-doping in a lanthanum strontium ferrite is presented as a successful approach to enhance the parent perovskite properties as both SOC air and fuel electrode. Structural, morphological and electrochemical characterizations of La0.6Sr0.4Fe0.995Pt0.005O3-δ (LSFPt005) are provided and compared to the undoped compound. LSFPt005-symmetric devices are tested as CO-SOFCs and CO2-SOECs at 850 °C, respectively, obtaining a maximum power density of 301 mW/cm2 and a current density of 0.82 A/cm2 at 1.5 V. Insights of cell operating mechanisms are provided through electrochemical impedance spectroscopy.

Effect of praseodymium valence change on the structure, magnetic, and microwave absorbing properties of M-type strontium ferrite: the mechanism of influence of citric acid dosage and calcination temperature

SrFe12-xPrxO19(x = 0–0.5) powders were synthesized and the effects of praseodymium doping amount, citric acid dosage, and calcination temperature on its structure, magnetic properties, and microwave absorbing properties were studied. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that praseodymium doping leads to the lattice expansion and makes strontium ferrite easier to form spherical polyhedron in microscopic morphology. The Fe2O3 impurity phase disappears and FePr1-ySryO3-δ impurity phase appears with the increase of the calcination temperature. It was inferred from Raman spectra and X-ray photoelectron spectroscopy that some Pr3+ ions form Pr4+ ions and the latter may occupy iron or strontium sites, and the transition from the Fe3+ to Fe2+ may occur at 4f2 site. The vibrating sample magnetometer results show that the saturation magnetization decreases first and then increases; the coercivity increases and the anisotropy field decreases after doping praseodymium. Praseodymium-doped strontium ferrite has strong absorption in low frequency band (C-band) or medium frequency band (X-band), while the matching thickness corresponding to high frequency band (Ku-band) is small. The maximum reflection loss reaches −50.95 dB and the effective absorption bandwidth (RL < −10 dB) is 4.76 GHz. Increasing the calcination temperature or doping amount will reduce the matching thickness, while increasing the amount of citric acid will disperse the grains and reduce the dielectric loss. It can be concluded that praseodymium valence change leads to the increase of Fe2+ ions and oxygen defects and there is also interface polarization between M-phase and heterogeneous phase, which together increases the dielectric loss of the material. Meanwhile, praseodymium doping can significantly increase the magnetic loss caused by natural resonance. These show that praseodymium doping improves the impedance matching of the material, increases the attenuation constant, and significantly improves the wave absorption performance.

Solid-State Electrochemical Thermal Transistors with Strontium Cobaltite–Strontium Ferrite Solid Solutions as the Active Layers

Thermal transistors have potential as thermal management devices because they can electrically control the thermal conductivity (κ) of the active layer. Recently, we realized solid-state electrochemical thermal transistors by utilizing the electrochemical redox reaction of SrCoOy (2 ≤ y ≤ 3). However, the guiding principle to improve the on/off κ ratio has yet to be clarified because the κ modulation mechanism is unclear. This study systematically modulates κ of SrCo1-xFexOy (0 ≤ x ≤ 1, 2 ≤ y ≤ 3) solid solutions used as the active layers in solid-state electrochemical thermal transistors. When y = 3, the lattice κ of SrCo1-xFexOy is ∼2.8 W m-1 K-1 and insensitive to x. When x = 0 and y = 3, κ increases to ∼3.8 W m-1 K-1 due to the contribution of the electron κ. When y = 2, κ slightly depends on the ordered atomic arrangement. Materials that are high electrical conductors with highly ordered lattices when the transistor is on but are electrical insulators with disordered lattices when the transistor is off should be well-suited for the active layers of solid-state electrochemical thermal transistors.

Development of sustainable strontium ferrite graphene nanocomposite for highly effective catalysis and antimicrobial activity

Graphene oxide (GO) has layered structure with carbon atoms that are highly coated with oxygen-containing groups, increasing the interlayer distance while simultaneously making hydrophilic atomic-thick layers. It is exfoliated sheets that only have one or a few layers of carbon atoms. In our work, Strontium Ferrite Graphene Composite (SF@GOC) has been synthesized and thoroughly characterized by physico-chemical methods like XRD, FTIR, SEM–EDX, TEM, AFM, TGA and Nitrogen adsorption desorption analysis. A very few catalysts have been manufactured so far that are capable of degrading Eosin-Y and Orange (II) dyes in water by heterogeneous catalytic method. The current study offers an overview of the recyclable nanocomposite SF@GOC used in mild reaction conditions to breakdown the hazardous water pollutant dyes Eosin-Y (96.2%) and Orange (II) (98.7%). The leaching experiment has demonstrated that the use of the transition metals strontium and iron have not result in any secondary contamination. Moreover, antibacterial and antifungal assay have been investigated. SF@GOC has shown greater activity with bacterial and fungal species while compared with GO. FESEM analysis shows that the bactericidal mechanism for SF@GOC is same in both gram-negative bacteria. The difference in the antifungal activity among the candida strains can be correlated with the movement of ions release (slower and faster) of synthesized nanoscrolls in SF@GOC. In comparison to previous reports, this new environmentally safe and novel catalyst showed substantial degrading activity. It can also be applied to new multifunctional processes such as in the fields of composite materials, solar energy, heterogeneous catalysis and biomedical applications.

Estimation of neutron and gamma-ray attenuation characteristics of some ferrites: Geant4, FLUKA and WinXCom studies

Ferrites are ceramic oxide materials consisting of mainly iron oxide and they have become massively important materials commercially and technologically, having a multitude of uses and applications. The protection against neutron–gamma mixed radiation is crucial in several nuclear applications. From this standpoint, mass attenuation coefficient, radiation protection efficiency and transmission factor of some ferrites namely barium, strontium, manganese, copper and cadmium ferrite has been computed using Geant4 and FLUKA simulations. Based on the simulated mass attenuation coefficient, other significant parameters such as linear attenuation coefficient, effective atomic and electron number, conductivity, half value layer, and mean free path were calculated for the selected ferrite materials. The validation of Monte Carlo geometry has been provided by comparing the mass attenuation coefficient results with standard WinXCom data. Gamma ray exposure buildup factors were computed using geometric progression fitting formula for the chosen ferrites in the energy range 0.015–15 MeV at penetration depths up to 40 mfp. The findings of the present work reveal that among the studied ferrites, barium ferrite and copper ferrite possess superior gamma ray and fast neutron attenuation capability, respectively. The present work provides a comprehensive investigation of the selected iron oxides in the field of neutron and gamma ray.

Absorption-Dominant mmWave EMI Shielding Films with Ultralow Reflection using Ferromagnetic Resonance Frequency Tunable M-Type Ferrites

HighlightsA novel multi-band absorption-dominant electromagnetic interference (EMI) shielding film with transition metal-doped M-type strontium ferrites composite layer and a conductive grid is developed.This film shows (1) ultralow EMI reflection less than 5%, (2) in multiple mmWave frequency bands corresponding to ferrites and grid characteristics, (3) with a broadband EMI shielding performance over 99.9% from 40 to 90 GHz.

Influence of the magnetic field during injection molding on the mechanical behavior of thermoplastic copolyester elastomers filled with strontium ferrite

Influence of the magnetic field during injection molding on the mechanical behavior of thermoplastic copolyester elastomers filled with strontium ferrite

Structure and magnetic properties of Al3+ substituted M-type SrLaCo hexaferrite

M-type hexagonal ferrites (SrFe12O19) have attracted much attention as a widely used permanent magnet. Many studies have been done to improve permanent magnetic properties. In particular, the formula of La–Co co-replaced Sr–Fe has achieved higher performance. However, no one has studied the influence of a small amount of Al ions on the above formula. In this study, the Al3+ ion substituted M-type Sr0.7La0.3Fe11.75ￚxAlxCo0.25O19 (0 ​≤ ​x ​≤ ​0.12) hexagonal ferrites were synthesized by solid state reaction. The crystalline structure was investigated by using X-ray diffraction (XRD) and the Rietveld refining method. The morphological of powder and magnetically oriented bulk were observed by scanning electron microscopy (SEM), and magnetic properties were measured by physical property measurement system-vibrating sample magnetometer (PPMS-VSM) techniques. The results show that a single M-type strontium ferrite was obtained with the Aluminum (Al) content (x) from 0 to 0.08, and the impure phase appeared when x was 0.12. The lattice parameters a and c both decreased with the increasing Al3+ content. SEM images indicate the hexagonal platelet-like particles and the size of the magnetic powders about 2–5 ​μm, and the powders are easily arranged in one direction under a magnetic field. The saturation magnetization (Ms) of the hexaferrite decreased with the increase of x from 0 to 0.12, but coercivity (Hc) of the magnetic powders increased with Al3+ content (x) from 0 to 0.12.

Effect of multi-wall carbon nanotubes/strontium ferrite nanoparticles on the microstructure, phase, magnetic and electromagnetic behavior of carbon aerogel composites

This research examined the electromagnetic behavior of a carbon aerogel composite containing multi-wall carbon nanotubes and strontium ferrite nanoparticles within the X band range (8.12–2.4 GHz). For this purpose, 10 wt% of carbon nanotubes and 5 wt%, 10 wt%, and 15 wt% of strontium ferrite nanoparticles were applied in the pyrolyzed cellulose aerogel composite. For structural and magnetic characterization of the samples, different techniques such as X-ray diffraction test, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, vector network analyzer, and vibrational magnetometer (VSM) were used. The VSM results indicated that the presence of 10 wt% strontium ferrite nanoparticles in the carbon aerogel substrate caused saturation magnetization of 2.31 emu/g. However, upon adding 10 wt% carbon nanotubes, the saturation magnetization value reached 6.82 emu/g. Based on the results, the greatest shielding efficiency (within the X-band = 110 ± 0.8 dB) occurred in the sample containing 10 wt% carbon nanotube alongside 5 wt% strontium ferrite at thicknesses of 4 mm. Furthermore, the reflection loss value of this sample was −48.59 ± 0.5 dB at a thickness of 3 cm and a frequency of 10.92 GHz.

Crystal structure and magnetic properties of Ga-Mn cosubstituted M-type strontium ferrite synthesized by sol-gel method

The M-type hexagonal strontium ferrites substituted by Gd-Mn ions were synthesized by the sol-gel self-combustion method. The synthesized samples were researched by X-ray diffraction (XRD), Fourier transform infrared spectroscopy analysis (FT-IR), scanning electric microscopy (SEM), and vibrating sample magnetometer (VSM). The XRD and the FT-IR results show that the pure M-type hexagonal ferrites phase is successfully obtained in the samples with the substitution amount (x) from 0.00 to 0.09 of Gd-Mn. The VSM results show that, as the substitution amount (x) of Gd-Mn increases, the remanent magnetization (Mr) and saturation magnetization (Ms) of the Sr1-xGdxFe12-xMnxO19 gradually increase, and the maximum values of 39.53 emu/g and 23.73 emu/g were obtained when x = 0.09. When x continues to increase, Mr and Ms decrease slightly, but they are still higher compared with those of the unsubstituted one. The coercivity (Hc) of the samples after doping is much higher than the coercivity of the pure sample, but as the substitution amount x increases, the coercivity first increases and then decreases, while the maximum value of Hc is 6738 Oe at x = 0.06.

Effect of Zn2+-Sn4+ co-substitution on structural and magnetic properties of SrFe12-2xZnxSnxO19 (x = 0–2) M-type strontium ferrite

We studied the structure and magnetic properties of Zn2+-Sn4+ co-substituted M-type strontium ferrite by X-ray diffraction (XRD), Fourier transformer infrared (FT-IR) spectroscopy, Raman spectroscopy, scanning electron microscopy (SEM), and superconducting quantum interference device magnetometer (SQUID-VSM). The lattice constants a and c increase monotonically with increasing substitution x, which is primarily attributed to the fact that the ionic radii of Zn2+ and Sn4+ are larger than those of Fe3+. The room temperature magnetic measurement results indicate that the saturation magnetization (Ms) can reach the maximum value Ms = 77 emu/g when x = 0.25, originating from the occupation of Zn2+ and Sn4+ in the spin-down 4f1 and 4f2 sites, respectively. Next, when x ≥ 0.5, the nonmagnetic Zn2+ and Sn4+ weaken the superexchange interaction, resulting in a monotonic decrease in saturation magnetization and coercivity. The sample with x = 0.25 has the optimum magnetic properties of Ms = 77 emu/g, Mr = 35 emu/g and Hc = 2203 Oe, and it is a promising candidate for high-density magnetic recording materials.

Enhanced magnetic properties of Sr0.7Ce0.3Fe11.7Zn0.3O19 by tuning pre-sintering temperature

In this work, pre-sintering temperature was tuned to investigate its effect on the structural and magnetic properties of oriented M-type hexagonal strontium ferrite Sr0.7Ce0.3Fe11.7Zn0.3O19. X-ray diffraction pattern shows that Fe2O3 and CeO2 impurity phases exist in all samples. As pre-sintering temperature increased, both saturation magnetization (Ms) and remanence ratio (Mr/Ms) first increased and then decreased. In contrast, coercivity (Hc) and magnetocrystalline anisotropy field (Ha) first decreased and then increased as pre-sintering temperature went up. The average grain size (D) increases monotonously with pre-sintering temperature. At pre-sintering temperature of 1200 ℃, Sr0.7Ce0.3Fe11.7Zn0.3O19 achieved optimal magnetic properties of Ms = 58.24 emu/g, Mr/Ms = 0.95, Hc= 1816 Oe, Ha= 10433 Oe and K1 = 1.51 × 105 J/m3. This work shows that the magnetic properties of M-type hexagonal strontium ferrite could be significantly improved by optimizing the pre-sintering temperature, which helps the design of high-performance and self-biased circulator.

Structural, magnetic, and photocatalytic properties of core–shell reversal nanocomposites of titanium-doped strontium ferrite and silica

Structural, magnetic, and photocatalytic properties of core–shell reversal nanocomposites of titanium-doped strontium ferrite and silica

Properties of Perovskite-like Lanthanum Strontium Ferrite Ceramics with Variation in Lanthanum Concentration

The purpose of this work is to study the effect of lanthanum (La) concentration on the phase formation, conductivity, and thermophysical properties of perovskite-like strontium ferrite ceramics. At the same time, the key difference from similar studies is the study of the possibility of obtaining two-phase composite ceramics, the presence of various phases in which will lead to a change in the structural, strength, and conductive properties. To obtain two-phase composite ceramics by mechanochemical solid-phase synthesis, the method of the component molar ratio variation was used, which, when mixed, makes it possible to obtain a different ratio of elements and, as a result, to vary the phase composition of the ceramics. Scanning electron microscopy, X-ray phase analysis, and impedance spectroscopy were used as research methods, the combination of which made it possible to comprehensively study the properties of the synthesized ceramics. Analysis of phase changes depending on lanthanum concentration change can be written as follows: (La0.3Sr0.7)2FeO4/LaSr2Fe3O8 → (La0.3Sr0.7)2FeO4/LaSr2Fe3O8/Sr2Fe2O5 → (La0.3Sr0.7)2FeO4/Sr2Fe2O5. Results of impedance spectroscopy showed that with an increase in lanthanum concentration from 0.10 to 0.25 mol in the synthesized ceramics, the value of the dielectric permittivity increases significantly from 40.72 to 231.69, the dielectric loss tangent increases from 1.07 to 1.29 at a frequency of 10,000 Hz, and electrical resistivity decreases from 1.29 × 108 to 2.37 × 107 Ω∙cm.