Strontium Iron Oxide Research Articles

Synthesis of surface-engineered SrFe2O4 for efficient catalytic partial oxidation of methane

In this study, a series of platinum (Pt)-doped strontium iron oxide (SrFe2O4) catalysts with varying particle sizes were synthesized through the four different catalysis synthesis methods such as solution combustion synthesis (SCS), co-precipitation (Co-PPT), oxalic acid assisted sol-gel (OXA) and, hydrothermal (HT). The objective was to investigate the impact of particle size on the catalytic activity and long-term stability of these four catalysts. The XRD and Raman results confirmed the formation of the SrFe2O4 perovskite structure. HRTEM, SEM, and other characterizations revealed a clear correlation between the synthesis conditions and the resulting particle sizes. The highest%CH4 conversion was around 95 % for the catalyst prepared through Solution combustion synthesis and the catalyst was found to be thermally stable up to. 100 h at 800 °C with a negligible variation of conversion while maintaining the H2/CO ratio at 2.0. To gain insight into catalytic activity, stability, and selectivity of catalysts we have performed Temperature-programmed surface reaction (TPSR) at a controlled temperature ramping program. This study also includes the study of coke deposition on the spent catalysts through different characterization techniques. Furthermore, we have performed a kinetic study to find the initial rate of the reaction and the activation energy of the Pt-doped SrFe2O4 catalyst and it has been found that activation energy was 35 KJ/mol for the catalyst Pt/SrFe2O4 synthesis through the solution combustion method.

“Quasi-In Situ Synthesis of Oxygen Vacancy-Enriched Strontium Iron Oxide Supported on Boron-Doped Reduced Graphene Oxide to Elevate the Photocatalytic Destruction of Tetracycline”

The efficient use of visible light is necessary to take advantage of photocatalytic processes in both indoor and outdoor circumstances. Precisely manipulating the in situ growth method of heterojunctions is an effective way to promote photogenerated charge separation. Herein, the SrFeO3@B-rGO catalyst was prepared by an in situ growth method. At a loading of 10 wt % B-rGO, the nanocomposites revealed an excellent morphology and thermal, optical, electrochemical, and mechanical properties. X-ray diffraction analysis revealed the cubic spinel structure and a space group of Pm̅3m for SrFeO3. High-resolution scanning electron microscopy and high-resolution transmission electron microscopy show the core-shell formation between SrFeO3 and B-rGO. Furthermore, density functional theory of SrFeO3 was performed to find its band structure and density of states. The SrFeO3@B-rGO nanocomposite shows the degradation rate of tetracycline (TC) reaching 92% in 75 min and the highest rate constant of 0.0211 min-1. To improve the catalytic removal rate of antibiotics, the efficiency of e- and h + separation must be improved, as well as the generation of additional radicals. Radical trapping tests and the electron paramagnetic resonance method indicated that the combination of Fe2+ and Fe3+ in SrFeO3 effectively separated e- and h+ while also promoting the development of the superoxide anion (•O2-) to accelerate TC degradation. The entire TC degradation pathway using high-performance liquid chromatography and its mechanism were discussed. As a whole, this study delineates that photocatalysis is a viable strategy for the treatment of environmental antibiotic wastewater.

Electrochemical control and protonation of the strontium iron oxide SrFeOy by using proton-conducting electrolyte

To electrochemically control structural and transport properties of oxygen-deficient perovskite SrFeOy (2.5 ≦ y ≦ 3) (SFO) epitaxial films, we employed electric-field-effect transistor structures in which the proton-conducting solid electrolyte Nafion is used as a gate insulator. When a positive gate voltage (VGS) is applied and protons are injected toward the film channel layer, the SFO films are electrochemically reduced, leading to increases in the channel resistance. On the other hand, when a negative VGS is applied and protons are removed, the SFO films are oxidized, and as a result, the channel resistances decrease. In addition, we found that the electrochemically reduced SFO films accommodate protons, forming the proton-containing oxide HxSrFeO2.5 whose proton concentration is determined by elastic recoil detection analysis to be x ∼ 0.11. Our results indicate the usefulness of the proton-conducting solid electrolyte for electrochemically controlling transition metal oxides and for exploring proton-containing oxides.

Solid-state electrochemical redox control of the optoelectronic properties for SrFeOx thin films

By utilizing redox reactions, the physical properties of several transition metal oxides can be drastically changed, which is useful for developing multifunctional memory devices. Strontium iron oxide (SrFeOx), which exhibits a clear phase transition from antiferromagnetic insulator (x = 2.5) to helimagnetic metal (x = 3), is a good candidate for the active material in multifunctional memory devices. However, practical applications using previous demonstrations of redox reactions in SrFeOx are limited by the use of a liquid electrolyte due to the leakage problem. Here, we demonstrate solid-state electrochemical redox reaction in SrFeOx using a yttria-stabilized zirconia (YSZ) single-crystal substrate as the solid electrolyte. We fabricated the SrFeO2.5 film on the YSZ substrate and the applied electric current using Au electrodes. The phase gradually changed from SrFeO2.5 to SrFeO2.5+x and SrFeO3−x. The color of the film changed from yellowish-transparent to dark brown. Although the as-grown SrFeO2.5 film showed high resistivity (ρ > 101 Ω cm), the ρ dramatically decreased (∼10−2 Ω cm) with increasing the applied charge density. Simultaneously, the thermopower greatly decreased from ∼+200 to ∼−10 μV K−1. The present results would provide a design concept for future SrFeOx-based solid-state multifunctional memory devices.

Quantitative analysis of the platinum surface decoration on lanthanum strontium iron oxide thin films via online-LASIL-ICP-MS

Solid oxide fuel cells (SOFCs) are one of the key technologies on the way to environmentally friendly power generation. Current research activities aim to reduce their operational temperature to intermediate temperatures (400–600 °C) to make their application more feasible. In a recent approach, lanthanum strontium iron oxide (LSF) thin film electrodes, a mixed ionic electronic conducting (MIEC) material, was decorated with tiny amounts of platinum nanoparticles, which led to a significant improvement of the oxygen reduction kinetics. To understand this material combination a precise characterization is of major interest, especially the exact amount of platinum on the surface. As the studied model-type thin film electrode requires a platinum current collector buried beneath the LSF to improve in-plane electron conductivity, a method providing quantitative information as well as sufficient depth resolution is needed.In this work, we further improved the recently presented approach of online laser ablation of solids in liquids (LASIL), which enabled in combination with ICP-MS detection a spatially resolved analysis of the sample composition. Careful optimization of laser parameters and carrier solution led to a depth resolution of 30 nm, which allowed a clear separation of the Pt-signals from the surface decoration and the underlying current collector. The amount of platinum on the surface was determined using calibration with a matrix matched standard and validated by another method. Finally, the imaging capabilities of the proposed online-LASIL approach have been employed to assess the homogeneity of the Pt-decoration, indicating significant variations within the investigated area. Thus, further improvements in the electrochemical properties of the investigated LSF electrodes could be anticipated by fabrication of MIECs with a more homogeneous platinum decoration.

Demonstration Reactor System for the Indirect Solar-Thermochemical Reduction of Redox Particles—The Particle Mix Reactor

Abstract In contrast to thermal receivers that provide heat for steam cycles, in solar thermochemistry often receiver-reactors are used, where materials undergo a reaction while being irradiated by concentrated sunlight. When applied to two-step redox cycles, multiple processes take place in such receiver-reactors, though on different timescales. This leads to design compromises and to high technical requirements for the implementation. A concept for an indirect particle-based system for thermochemical cycles was therefore proposed in which the heat required for the reduction of redox particles is provided by inert heat transfer particles that absorb concentrated solar radiation in a dedicated particle receiver. The novel and central component in this indirect system is the particle mix reactor. It functions by mixing the two particle types for heat transfer and establishing a controlled atmosphere under decreased oxygen partial pressures in a common reactor chamber. The design of an experimental setup for demonstration and investigation of the particle mix reactor is presented in this work. Potential operation modes and design options for particle heater, mixing unit, and oxygen partial pressure decrease are discussed and illustrated. The selection of a mixer type is based on the homogeneity of the obtained mixture. It is supported by the use of discrete element method (DEM) simulations, which were compared to experimental results from a separate setup. Heat loss estimations for the mixing process in the selected mixer geometry are performed for alumina heat transfer particles and strontium iron oxide redox particles. The components' geometries, the overall experimental setup design, as well as operation steps are presented.

Impact of calcium doping on structure, catalytic and conductive properties of lanthanum strontium iron oxide

A set of dense structure materials based on La0.5Sr0.5-xCaxFeO3 with different amount of calcium (where x varies from 0 to 0.1) were prepared. It was found that with calcium addition the hexagonal perovskite La0.5Sr0.5FeO3 structure is preserved and Ca2+ ions accommodate themselves easily in the lattice. The sintered ceramics have homogeneous microstructure and uniform grain size distribution with the average size which increases with Ca addition. Electrical properties of the sintered materials determined by the DC method revealed an increase in sample conductivity with Ca2+ doping. An increase in structure stability with the increase of calcium addition was also confirmed by the temperature-programmed studies.

Synthesis and Characterization of Nano Strontium Ferrite and its gas sensing studies

Glass-Self-propagating low temperature (SPLT) route for synthesizing nanomaterials has been gaining importance in the field of synthetic technology by being a cost effective, faster and cleaner approach when compared to the other conventional and wet chemical methods for the synthesis of metal oxide nanoparticles. In the present work, synthesis of strontium iron oxide (SrFe2O3) nanoparticles viz., were carried out by SPLT route through the thermal decomposition of strontium iron metal oxalate precursors employing polyvinyl alcohol (PVA) as a fuel. The characterization was developed for size and structure by employing Fourier transform infrared (FTIR) spectral studies. The morphology of the samples ranged from nano spherical to agglomerated irregular-shaped particles for strontium ferrite samples based on the results of field emission scanning electron microscopy (FESEM) images. Possible gas sensing applications of these ferrite sample nanoparticles are studied.

Development of rare earth free permanent magnet generator using Halbach cylinder rotor design

Direct-drive permanent magnet generators (DDPMGs) offer increased reliability and efficiency for wind turbine application over the more commonly used geared doubly-fed induction generators. However, deployment of DDPMGs is limited in the U.S. wind industry due to reliance on NdFeB permanent magnets, which contain critical rare earth elements Nd and Dy. To allow for the use of lower energy density, rare earth free permanent magnets, Halbach cylinders are employed as the rotor in a 3.5 kW PMG to concentrate magnetic flux over the rotor surface and increase magnetic loading. By varying the slot-to-pole ratio in Halbach PMGs (HPMGs), designs are developed, which allow for the use of ceramic, or hard ferrite, strontium iron oxide permanent magnets. At the 3.5 kW scale, the ceramic HPMGs are able to achieve rated performance at reduced average efficiency of between 82 and 87%, which is due to the difference in permanent magnet material properties. For scaling of the ceramic HPMGs to 3 MW, rated performance and high efficiency were achieved on average at rated speed, demonstrating the potential for a rare earth free PMG in commercial scale wind turbines.

Electrochemical investigations of cobalt-free perovskite cathode material for intermediate temperature solid oxide fuel cell

A novel cobalt-free perovskite zinc-doped lanthanum strontium iron oxide (La0.8Sr0.2ZnxFe1−xO3−δ, LSZF, x = 0.1–0.3) is synthesized and evaluated as cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC) with samarium doped ceria (SDC) electrolyte. LSZF cathode at x = 0.2 composition demonstrates the remarkable electrochemical activity at intermediate temperature (550 °C): such as, high electrical conductivity (13.63 S cm−1), excellent thermal stability with SDC electrolyte (12.10 μK−1), high surface area (4.52 m2 g−1), extremely reduced area specific resistance (0.69 Ω cm−2) and low activation energy (0.117 eV). Furthermore, single fuel cells are fabricated using LSZF as a cathode, which exhibits the excellent performance by achieving the high power density of 409 mW cm−2 under natural gas as a fuel and ambient air as an oxidant at 550 °C with good stability over 10 h. All experimental results indicate that the LSZF is a promising cathode material for natural gas based intermediate temperature fuel cell applications.

Magnetic field-induced switching of magnetic ordering in SrFeO3−δ

The oxygen-deficient strontium iron oxide SrFeO3−δ (SFO) exhibits richness in the phase diagram over a broad range of temperatures and for other external parameters. Room-temperature X-ray diffraction and Raman spectrum reveals that the structure of synthesized SFO system consists of two mixed phases, i.e., major orthorhombic and minor tetragonal phases. The low-temperature Raman and vibrating sample magnetometer measurements indicated a structural transition below 253 K. The magnetic property of the synthesized SFO for various external magnetic field (up to 5 T) reveals possible variation in oxygen stoichiometry. Also, the application of external H increases Neel transition temperature (T N), suppresses the hysteresis width (W H), and thus weakens the first-order nature of the transition. Our analysis revealed the vanishing of hysteresis and the first-order antiferromagnetic transition becomes a crossover above a critical magnetic field H CR ≈ 5 T. Possible switching of magnetic ordering and oxidation state observed in same system enhances interest in related compounds which may be used in magnetic sensors and other magnetic switching devices.

Metallic conductivity in infinite-layer strontium iron oxide thin films reduced by calcium hydride

Single-crystalline epitaxial SrFeO2 thin films were grown on perovskite substrates with various lattice parameters by combining pulsed laser deposition method with solid-phase reduction using CaH2, and these structural and transport properties were investigated. The highly crystalline films prepared on lattice-matched KTaO3(0 0 1) substrate exhibited metallic conduction, while those prepared on SrTiO3(0 0 1) and DyScO3(1 1 0) substrates were insulating films, in analogy to bulk SrFeO2. From Hall measurements on the metallic SrFeO2 films, the conduction carriers were determined to be n-type (i.e., electrons) with a carrier density of 3.1 × 1018 cm−3 and a mobility of 10.2 cm2 V−1 s−1 at 300 K. It is suggested that the electron carriers are supplied by oxygen vacancies or hydrogen ions in the metallic SrFeO2 films.

Magnetic Bioactive SrFe12O19-SiO2-CaO-Na2O-P2O5 Glass-Ceramics for Hyperthermia Treatment of Bone Cancer

The magnetic bioglass-ceramics were introduced for hyperthermia treatment of bone cancer. The aim of this work was to study the magnetic properties of ferrimagnetic glass-ceramics from SrFe12O19(SF)-SiO2-CaO-Na2O-P2O5 system by using the modified solid-state sintering method. The results showed that sodium calcium silicate (Na4Ca4Si6O18), strontium iron oxide (SrFe12O19) and iron oxide (Fe2O3) were precipitated in all samples. The saturation magnetization (Ms), remanence (Mr) and coercivity (Hc) increased by the addition of SF in the bioglass. The samples were soaked in simulated body fluid (SBF) for 14 days in order to investigate the bioactivity of the samples in vitro. The apatite layer was found on the surface of all bioglass-ceramics confirming their biocompatibility and it increased with increasing strontium ferrite content.

A novel approach for synthesis of M-type hexaferrites nanopowders via the co-precipitation method

M-type hexaferrites; barium hexaferrite BaFe12O19 and strontium hexaferrite SrFe12O19 powders have been successfully prepared via the co-precipitation method using 5 M sodium carbonate solution as alkali. Effects of the molar ratio and the annealing temperature on the crystal structure, crystallite size, microstructure and the magnetic properties of the produced powders were systematically studied. The results indicated that a single phase of barium hexaferrite was obtained at Fe3+/Ba2+ molar ratio 12 annealed at 800–1,200 °C for 2 h whereas the orthorhombic barium iron oxide BaFe2O4 phase was formed as a impurity phase with barium M-type ferrite at Fe3+/Ba2+ molar ratio 8. On the other hand, a single phase of strontium hexaferrite was produced with the Fe3+/Sr2+ molar ratio to 12 at the different annealing temperatures from 800 to 1,200 °C for 2 h whereas the orthorhombic strontium iron oxide Sr4Fe6O13 phase was formed as a secondary phase with SrFe12O19 phase at Fe3+/Sr2+ molar ratio of 9.23. The crystallite sizes of the produced nanopowders were increased with increasing the annealing temperature and the molar ratios. The microstructure of the produced single phase M-type ferrites powders displayed as a hexagonal-platelet like structure. A saturation magnetization (53.8 emu/g) was achieved for the pure barium hexaferrite phase formed at low temperature 800 °C for 2 h. On the other hand, a higher saturation magnetization value (Ms = 85.4 emu/g) was obtained for the strontium hexaferrite powders from the precipitated precursors synthesized at Fe3+/Sr2+ molar ratio 12 and thermally treated at 1,000 °C for 2 h.

Ba2Mn2O4Cu0.9S: A layered Oxysulfide with a New Perovskite-Related Manganese Oxide Fragment

The oxysulfides Ba2Mn2O4Cu0.9S and Ba1.3Sr0.7Mn2O4CuS are reported. The compounds crystallize in space group P4/nmm with 2 formula units in the unit cell and lattice parameters a = 3.9916(1) Å and c = 19.5628(5) Å for a refined composition of Ba2Mn2O4Cu0.89(1)S and a = 3.9595(1) Å and c = 19.2227(3) Å for Ba1.32(3)Sr0.68(4)Mn2O4Cu0.98(2)S determined, respectively, from powder neutron and X-ray single-crystal diffraction measurements. The structure consists of alkaline earth Manganite slabs composed of MnO5 square-based pyramids sharing edges and vertexes, which are separated by CuS antifluorite-type puckered layers. The central part of the alkaline earth manganite slab is composed of MnO5 square-based pyramidal units sharing all four of their basal edges with neighboring units in the basal plane and sharing their apical vertices with those of square-based MnO5 pyramids in the outer part of the alkaline earth manganite slab. This is similar to a structural fragment in the as-yet-unrealized strontium iron oxide Sr4Fe6O12, which is the oxide-poor relative of the anion-conducting Sr4Fe6O13±δ phases. The intrinsic copper deficiency in semiconducting Ba2Mn2O4Cu0.9S suggests a mean manganese oxidation state of +2.55. The results of magnetic susceptibility measurements and low-temperature neutron diffraction results suggest that some moments participate in long-range antiferromagnetic order, whereas others give rise to spin-glass-like behavior.

Mechanically induced oxidation of SrFeO 3−δ

The nonstoichiometric strontium–iron oxide SrFeO 3−δ (2.5 ≤ 3 − δ ≤ 3.0) exhibits richness of equilibrium states over a broad range of temperatures and oxygen partial pressures. Its oxidation induced by ball milling was investigated. The mechanical treatment of the material at room temperature in oxygen atmosphere was found to cause the reaction. However, the product differs from compounds obtained by annealing, due to crystal imperfections introduced by milling. The changes in the oxygen stoichiometry, the crystal structure, and the morphology of the powder are discussed.

ChemInform Abstract: ANODIC CHARACTERISTICS OF SUBSTITUTED STRONTIUM IRON OXIDE (SRFE0.9M0.1O3) (M = NICKEL, COBALT, TITANIUM, MANGANESE) ELECTRODES

Chemischer InformationsdienstVolume 11, Issue 33 Physical Inorganic Chemistry ChemInform Abstract: ANODIC CHARACTERISTICS OF SUBSTITUTED STRONTIUM IRON OXIDE (SRFE0.9M0.1O3) (M = NICKEL, COBALT, TITANIUM, MANGANESE) ELECTRODES Y. MATSUMOTO, Y. MATSUMOTOSearch for more papers by this authorJ. KURIMOTO, J. KURIMOTOSearch for more papers by this authorE. SATO, E. SATOSearch for more papers by this author Y. MATSUMOTO, Y. MATSUMOTOSearch for more papers by this authorJ. KURIMOTO, J. KURIMOTOSearch for more papers by this authorE. SATO, E. SATOSearch for more papers by this author First published: August 19, 1980 https://doi.org/10.1002/chin.198033017Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume11, Issue33August 19, 1980 RelatedInformation