Search Results (26)

Four different-sized carbon microspheres, CS, obtained by a facile hydrothermal method, are applied as a hard template for the preparation of a series of macroporous LaFeO₃. The average particle size of the CS obtained is between 0.350 and 0.700 µm. The macroporous LaFeO₃ are tested in a Fenton-like activation of peroxymonosulfate, PMS, for oxidation of tetracycline hydrochloride, TCH, in model water solution under visible-light irradiation. The effect of parameters such as type of irradiation, temperature of the reaction, and type of the water matrixes was tested. The oxidation of the pollutant TCH is evaluated by total organic carbon and organic nitrogen measurements. The results showed the superior catalytic activity of macroporous LaFeO₃ in comparison to pure LaFeO₃. Rate constants between 0.036 and 0.184 min⁻¹ at 25 °C were obtained. The activation energy for the process with the most active macroporous LaFeO₃ was 33.88 kJ/mol, a value lower than for the catalytic process with PMS only, proving the positive role of the macroporous LaFeO₃ for TCH degradation. Radical scavenger measurements showed that singlet oxygen, produced during the catalytic degradation process, was responsible for the performance of macroporous LaFeO₃/PMS/visible light for TCH degradation. The catalysts proved to be efficient and recyclable. Full article

Gas-sensing technology is crucial for the detection of toxic and harmful gases to ensure environmental safety and human health. Gas sensors convert the changes in the conductivity of the sensing material resulting from the adsorption of gas molecules into measurable electrical signals. Rare earth orthoferrite-based perovskite oxides have emerged as promising candidates for gas-sensing technology owing to their exceptional structural, optical, and electrical properties, which enable the detection of various gases. In this article, we review the latest developments in orthoferrite-based gas sensors in terms of sensitivity, selectivity, stability, operating temperature, and response and recovery times. It begins with a discussion on the gas-sensing mechanism of orthoferrites, followed by a critical emphasis on their nanostructure, doping effects, and the formation of nanocomposites with other sensing materials. Additionally, the role of the tunable bandgap and different porous morphologies with a high surface area of the orthoferrites on their gas-sensing performance were explored. Finally, we identified the current challenges and future perspectives in the gas-sensing field, such as novel doping strategies and the fabrication of miniaturized gas sensors for room-temperature operation. Full article

The effect of the Mn³⁺ ion on the local distortions of FeO₆ octahedra in orthoferrite samples was investigated. Mössbauer spectroscopy measurements for a series of ${\mathrm{HoFe}}_{1-x}{\mathrm{Mn}}_x{\mathrm{O}}_3$ (x = 0–0.7) orthoferrite samples with the space group Pnma were carried out at temperatures above the Néel point (700 K). The electric field gradient (EFG) tensor on Fe ions for these compounds was found using first-principle calculations. The concentration dependence of quadrupole splitting was obtained using experimental and theoretical data. Mn³⁺ cations were found to affect the Mössbauer spectra mainly due to distortions of the crystal lattice. Theoretical calculations show that the values of all electric field gradient components increase significantly with the manganese concentration in the system, and the eigenvectors ${\mathbf{e}}_{\mathbf{xx}}$ and ${\mathbf{e}}_{\mathbf{yy}}$ of the electric field gradient tensor sharply change their direction at concentrations of x > 0.1. Full article

This study investigates the optical properties of yttrium ferrite thin films fabricated via pulse laser deposition. Yttrium orthoferrite, a ferrimagnetic material known for its potential applications in spintronics and photonics, was deposited on single-crystal substrates under controlled conditions to analyze its optical characteristics. The influence of deposition time on the film quality and optical properties was examined. Atomic force microscopy in contact mode revealed surface roughness variations up to 35 nm, indicating the films’ ability to cover substrate defects. Reflectance measurements determined the optical band gap, which decreased from 3.17 eV for thinner films (44 nm) to 2.91 eV for thicker films (93 nm). Forbidden electronic transitions were also observed, attributed to heteroepitaxial growth and phonon interactions. These results demonstrate the effect of film thickness on morphology and optical properties, making YFeO₃ films promising for a range of optoelectronic applications. Full article

B-site cobalt (Co)-doped rare-earth orthoferrites ReFeO₃ have shown considerable enhancement in physical properties compared to their parent counterparts, and Co-doped LuFeO₃ has rarely been reported. In this work, LuFe_1−xCo_xO₃ (x = 0, 0.05, 0.1, 0.15) powders have been successfully prepared by a mechanochemical activation-assisted solid-state reaction (MAS) method at 1100 °C for 2 h. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy studies demonstrated that a shrinkage in lattice parameters emerges when B-site Fe ions are substituted by Co ions. The morphology and elemental distribution were investigated by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The UV–visible absorbance spectra show that LuFe_0.85Co_0.15O₃ powders have a narrower bandgap (1.75 eV) and higher absorbance than those of LuFeO₃ (2.06 eV), obviously improving the light utilization efficiency. Additionally, LuFe_0.85Co_0.15O₃ powders represent a higher photocatalytic capacity than LuFeO₃ powders and can almost completely degrade MO in 5.5 h with the assistance of oxalic acid under visible irradiation. We believe that the present study will promote the application of orthorhombic LuFeO₃ in photocatalysis. Full article

There is an urgent need to develop a low-cost and high-performance gas sensor for industrial production and daily life. Perovskite-type oxides are appropriate materials for resistive gas sensors. In this paper, two gas-sensing materials of gadolinium orthoferrite (GdFeO₃) with rod and butterfly morphologies were obtained by annealing the corresponding precursors at 800 °C in a muffle furnace for 3 h. The precursors of GdFe(CN)₆·4H₂O with novel morphologies were prepared by a co-precipitation method at room temperature. The materials were evaluated in terms of their structure, morphology, and gas-sensing performance. The gas sensor based on GdFeO₃ rods showed a better sensing performance than the sensor based on GdFeO₃ butterflies. It exhibited the largest response value of 58.113 to 100 ppm n-propanol at a relatively low operating temperature of 140 °C, and the detection limit was 1 ppm. The results show that the GdFeO₃ rods-based sensor performed well in detecting low concentration n-propanol. The satisfactory gas-sensing performance of the GdFeO₃ rods-based sensor may be due to the porous structure and the large percentages of defect oxygen and adsorbed oxygen (37.5% and 14.6%) on the surface. This study broadens the application of GdFeO₃ in the gas sensor area. Full article

In this paper, powders consisting of o-EuFeO₃ nanoparticles were obtained by the co-precipitation method using two different precipitating agents (NH₃ and (NH₄)₂CO₃ solutions; corresponding products were denoted as samples S.1 and S.2, respectively) and followed by annealing for 1 h at 750, 850, and 950 °C. The magnetic, optical, and physicochemical characteristics of S.1 and S.2 were evaluated by means of EDXS (energy dispersive X-ray spectroscopy), PXRD (powder X-ray diffraction), TG/DSC (thermogravimetry/differential scanning calorimetry), FTIR (Fourier-transform infrared spectroscopy), TEM (transmission electron microscopy), UV-Vis DRS (Ultraviolet–Visible diffuse reflectance spectroscopy), and VSM (vibrating-sample magnetometry). The o-EuFeO₃ structure was shown to be stable at annealed temperatures, and t = 850 °C is recommended for synthesizing such substances. The average size of o-EuFeO₃ crystals is around 27 (S.1) and 34 nm (S.2). The results revealed a homogeneous distribution of the main elements on the samples’ surfaces, with morphology consisting of isometric and highly agglomerated nanoparticles. The bandgap value (E_g) of the synthesized samples was 2.31 (S.1) and 2.39 eV (S.2). Besides, these nanoparticles appeared to possess paramagnetic behavior. Full article

The synthesis of orthoferrites of the type La_1−xCe_xFeO_3+x/2, x = 0.00, 0.01, 0.03, 0.05, and 0.07, by applying a simple and effective mechanochemical transformation from the constituent oxides is presented. Physicochemical methods such as powder X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Vis spectroscopy, and Brunauer–Emmett–Teller (BET) adsorption were applied to gain information about the effect of Ce⁴⁺ content on the structural, textural, and optical properties of the samples. The catalytic activity of the samples for water decontamination was determined in a photo-Fenton-like activation of persulfate for removal of tetracycline hydrochloride as model pollutant. The presence of persulfate, PDS, considerably increased the removal efficiency under visible light illumination. Full article

In this paper, a series of Gd_1-xBi_xFeO₃ (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) nanoparticles have been readily synthesized by a green and facile sol–gel method. It gradually changed from the orthorhombic structure (space group Pbnm) to the rhombohedral perovskite structure (space group R3c). Weak ferromagnetic behavior was effectively induced by Bi³⁺, with reduced magnetization. It was closely related with the lattice distortion of the perovskite structure and modified interactions between Fe-O-Fe. Boosted photocatalytic activities of Gd_1-xBi_xFeO₃ were observed for the removal of methylene blue (MB) under the visible light irradiation. In particular, Gd_0.5Bi_0.5FeO₃ showed the optimum photocatalytic efficiency, in which the degradation efficiency reached 82.1% after 180 min of visible light illumination, with good stability and repeatability. The improved performance was mainly ascribed to enhanced visible light absorption, decreased optical band gap from 2.21 to 1.8eV and stronger charge transfer efficiency. A possible photocatalytic mechanism is also proposed according to the band structure. The results indicate that this system will be a promising candidate for the degradation of organic pollutant as a novel magnetically recoverable photocatalyst. Full article

LaFeO₃ perovskite ceramics have been prepared via reaction flash technique using Fe₂O₃ and La₂O₃ as precursors. The obtained pellets have been investigated using several techniques. The formation of LaFeO₃ has been clearly confirmed by X-ray diffraction. The scanning electron microscopy micrographs have shown the microporous character of the obtained pellets due to the low temperature and dwell time used in the synthesis process (10 min at 1173 K). The orthorhombic-rhombohedral phase transition has been observed at approximately 1273 K in differential thermal analysis measurements, which also allows us to determine the Néel temperature at 742 K. The fitted Mössbauer spectra exposed the presence of a single sextet ascribed to the Fe⁺³ ions in the tetrahedral site. Finally, magnetic measurements at room temperature indicate the antiferromagnetic character of the sample. Full article

Nanostructured hexagonal rare-earth orthoferrites (h-RfeO₃, R = Sc, Y, Tb-Lu) are well known as a highly effective base for visible-light-driven heterojunction photocatalysts. However, their application is limited by metastability, leading to difficulties in synthesis due to the irreversible transformation to a stable orthorhombic structure. In this work, we report on a simple route to the stabilization of h-YbFeO₃ nanocrystals by the synthesis of multiphase nanocomposites with titania additives. The new I-type heterojunction nanocomposites of o-YbFeO₃/h-YbFeO₃/r-TiO₂ were obtained by the glycine–nitrate solution combustion method with subsequent heat treatment of the products. An increase in the mole fraction of the h-YbFeO₃ phase in nanocomposites was found with the titanium addition, indicating its stabilizing effect via limiting mass transfer over heat treatment. The complex physicochemical analysis shows multiple contacts of individual nanocrystals of o-YbFeO₃ (44.4–50.6 nm), h-YbFeO₃ (7.5–17.6 nm), and rutile r-TiO₂ (~5 nm), confirming the presence of the heterojunction structure in the obtained nanocomposite. The photocatalytic activity of h-YbFeO₃/o-YbFeO₃/r-TiO₂ nanocomposites was evaluated by the photo-Fenton degradation of the methyl violet under visible light (λ ≥ 400 nm). It was demonstrated that the addition of 5 mol.% of TiO₂ stabilizes h-YbFeO₃, which allowed us to achieve a 41.5 mol% fraction, followed by a three-time increase in the photodecomposition rate constant up to 0.0160 min⁻¹. Full article

Rare-earth orthoferrites have found wide application in thermocatalytic reduction-oxidation processes. Much less attention has been paid, however, to the production of CeFeO₃, as well as to the study of its physicochemical and catalytic properties, in particular, in the promising process of CO₂ utilization by hydrogenation to CO and hydrocarbons. This study presents the results of a study on the synthesis of CeFeO₃ by solution combustion synthesis (SCS) using various fuels, fuel-to-oxidizer ratios, and additives. The SCS products were characterized by XRD, FTIR, N₂-physisorption, SEM, DTA–TGA, and H₂-TPR. It has been established that glycine provides the best yield of CeFeO₃, while the addition of NH₄NO₃ promotes an increase in the amount of CeFeO₃ by 7–12 wt%. In addition, the synthesis of CeFeO₃ with the participation of NH₄NO₃ makes it possible to surpass the activity of the CeO₂–Fe₂O₃ system at low temperatures (300–400 °C), as well as to increase selectivity to hydrocarbons. The observed effects are due to the increased gas evolution and ejection of reactive FeO_x nanoparticles on the surface of crystallites, and an increase in the surface defects. CeFeO₃ obtained in this study allows for achieving higher CO₂ conversion compared to LaFeO₃ at 600 °C. Full article

In this work, manganese (Mn)-doped YFeO₃, i.e., YFM_xO powders with 0 ≤ x ≤ 0.1, was synthesized by a hydrothermal method to study the influences of doping on its structural, morphological, optical, magnetic, and local electrical properties. The experimental results show that all the samples exhibit an orthorhombic structure with space group Pnma. Refined structure parameters are presented. Morphology images show the shape evolution from layered to multilayered with increasing Mn content. Infrared spectra reveal the characteristic vibrations of the obtained YFM_xO samples. From the magnetic study, an increased magnetic moment in the range of 0 ≤ x ≤ 0.075 is observed. The Fe and Y K-edge local structure studies indicate that the valency of Fe and Y is mainly found in the trivalent state, which also indicates that the substitution of Mn ions not only affects the nearest neighbor atomic shell of Fe but also affects the nearest neighbor’s local structure of Y atoms. Our results show that the addition of Mn exhibits an evident influence on the local structural and magnetic properties. Full article

In this manuscript, we present the synthesis of gadolinium orthoferrite nanoparticles using the sol–gel auto-combustion technique. The obtained gadolinium orthoferrite nanoparticles were annealed at various temperatures, such as 800 °C, 900 °C, 1000 °C, and 1100 °C. The synthesized materials were analyzed by various instrumental characterizations. The vibrational characteristics of the synthesized samples were verified by FTIR. The surface morphology of the gadolinium orthoferrite nanoparticles was analyzed by FE-SEM and HR-TEM, revealing their spherical structural morphology and uniform particle structure. The presence of the elemental features was analyzed in the gadolinium orthoferrite nanoparticles by EDAX. The surface analysis of the core ranges of the XPS-recorded spectra were obtained for the elemental states of the Gd, Fe, and O factors in the samples, and it additionally characterized the different levels of oxidative states by fitting the levels of the high-resolution parameters of Gd 4d, Fe 2p, and O 1s. The magnetic properties of the samples were investigated by VSM. The measurement of the magnetic parameters revealed that gadolinium orthoferrite nanoparticles exhibit a ferromagnetic nature. Full article

The YFeO₃ orthoferrite is one of the most promising materials for antiferromagnetic (AFM) spintronics. Most studies have dealt with bulk samples, while the thin YFeO₃ films possess unusual and variable properties. Ultrathin (3–50 nm) YFeO₃ films have been prepared by magnetron sputtering on the r-plane ($1\overline{1}02$)-oriented Al₂O₃ substrates (r-Al₂O₃). Their characterization was undertaken by the Mössbauer reflectivity method using a Synchrotron Mössbauer Source and by X-ray diffraction (XRD) including grazing incidence diffraction (GI-XRD). For thin films with different thicknesses, the spin reorientation was detected under the application of the magnetic field of up to 3.5 T. Structural investigations revealed a predominant orthorhombic highly textured YFeO₃ phase with (00l) orientation for relatively thick (>10 nm) films. Some inclusions of the Y₃Fe₅O₁₂ garnet (YIG) phase as well as a small amount of the hexagonal YFeO₃ phase were detected in the Mössbauer reflectivity spectra and by XRD. Full article