Fabrication and characteristics of Ce-doped Y3Fe5O12 ceramics by hot-press sintering with oxygen/nitrogen atmosphere

Infrared transparent Ce-doped Y₃Fe₅O₁₂ (Ce_: YIG, Ce_xY_3-xFe₅O_12, x = 0, 0.12, 0.24, 0.36) ceramics were successfully produced by the solid-state reaction using a hot-press sintering process from the Y₂O₃, Fe₂O₃, and CeO₂ powders. The phase structure, microstructure, infrared transmittance, and magnetic and magneto-optical properties of the Ce-doped Y₃Fe₅O₁₂ ceramics were measured and analyzed. The in-line transmittances of the Ce-doped Y₃Fe₅O₁₂ ceramics with the x = 0, 0.12, 0.24 (L = 0.5 mm) at 1550 nm were about 72%, 66.5%, and 57.6%, respectively. In the state of saturation magnetization, the Faraday rotation angle per centimeter (θ_F) of Ce_xY_3-xFe₅O₁₂ (x = 0, 0.12, 0.24) ceramics measured by the light extinction method was 182.5, −410.4, and −958.3 deg./cm, respectively. The change of the θ_F was about −142.5 deg./cm when per 1at.% Ce was substituted in the dodecahedral site of YIG materials. The (Ce_0.24Y_2.76)Fe₅O₁₂ ceramics were determined as the optimized composition for its excellent infrared optical and magneto-optical properties.     

Comparison of the catalytic performance of YIG garnets and Fe-containing oxides catalysts for oxidation of ethylbenzene

Iron-containing garnets (YIG) were used as catalysts for selective oxidation of ethylbenzene (EB) in the presence of H₂O₂ as oxidant. The catalysts comprising of two series of garnets e.g., Y₃(Fe_1–xZn_x)₅O₁₂ and Y₃(Fe_1–xNi_x)₅O₁₂ had distinct Zn and Ni contents (x = 0.00 0.01, 0.03, and 0.05). XRD, Raman and FTIR spectroscopies revealed that the cubic structure of Y₃Fe₅O₁₂ garnet was present for x = 0.00 and 0.01. For higher contents, the garnets had the Y₃Fe₅O₁₂ phase besides hematite (α-Fe₂O₃). The catalytic activity was dependent on the contents of metals in the garnets with Y₃Fe_4·97Ni_0·03O_12-γ and Y₃Fe_4·95Zn_0·05O_12-γ catalysts achieving better results. The influence of the reaction conditions such as reaction time, reaction temperature and effect of the solvents as well as the substrates to H₂O₂ molar ratios were studied. SEM-EDS, XPS and EPR results demonstrated the affinity of the Fe²⁺/Fe³⁺ pairs with Ni²⁺ species for the ethylbenzene molecule, which gave an EB conversion of 77% with a good production of acetophenone over the Y₃Fe_4·97Ni_0·03O_12-γ catalyst compared to other binary and ternary solids.     

Investigating the co-substitution impact of yttrium–nickel cations on lattice,morphological and magnetic parameters of SrM based ceramics

This study details the impact of the co-substitution of Y³⁺-Ni³⁺ ions for the Fe³⁺ ions on the structural, morphological and, magnetic parameters of SrM based SrY_xFe_12-2xNi_xO₁₉ (0.00 ≤ x ≥ 0.25) (SrYFeNiO) ceramic magnets synthesized by the ceramic route. Rietveld refinement of XRD confirmed the hexagonal (P63/mmc (194), z = 2) SrFe₁₂O₁₉ phase for all and an additional rhombohedral (R-3c (167), z = 6) hematite Fe₂O₃ phase for x = 0.2, x = 0.25 doping levels. The experimental and theoretical measurements abstracted the stretch of lattice parameters, i.e., the crystallographic axis and the lattice cell volume, and the dislocation of the crystallographic plane (1 1 4) for the hexagonal system, certified the heavy Y³⁺-Ni³⁺ ions substitution. To examine the morphological parameters, FESEM presented the regular hexagonal platelets of sizes ~ 1–2 μm, and EDX revealed the presence of constituent elements with their atomic and weight percentages in SrFeYNiO products. The extraction of vibrational frequencies of Fe–O bonds at tetrahedral and octahedral sites of iron through FT-IR spectroscopy authenticates the formation of the SrM phase. XPS correlated the doped elements, i.e., nickel in Ni⁺² and Ni⁺³ and yttrium in Y⁺³, whereas parent element, i.e., iron in Fe⁺³ and Fe⁺² chemical states, enlightened their impact on the magnetic parameters. Hysteresis loop analysis deduced a linear decline in magnetic parameters such as saturation magnetization (M_s) and remnant magnetization (M_r) due to non-magnetic Y³⁺ and less magnetic Ni³⁺ ions installment in 4f1 and 2b polyhedral sites of Fe³⁺ ions. However, high coercivity (H_c) up to 2.92 kOe ∈ x = 0.15 and extended magnetocrystalline anisotropy (MCA) up to 5.790× 10⁶ Erg/g ∈ x = 0.15 of our obtained ceramic magnets affirmed their application in permanent magnetic industry. M(T) curves also demonstrated the decrease in M_s and displayed an SPM at T_B, which is shifting towards lower temperatures with increasing Y³⁺-Ni³⁺ contents approved the expansion of lattice parameters.     

Multiple magnetic phase transitions in NixMn1-xCo2O4

We prepared pure-phase Ni_xMn_1-xCo₂O₄ (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni_xMn_1-xCo₂O₄ increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni_0.5Mn_0.5Co₂O₄ sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni_xMn_1-xCo₂O₄ (x = 0 and 0.25), and as the concentration of Ni increases, Ni_xMn_1-xCo₂O₄ (x = 0.75 and 1) show a spin glass state. The structure of Ni_xMn_1-xCo₂O₄ (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni_xMn_1-xCo₂O₄ and that the strength of the Ni-O bond is greater than that of the Mn-O bond.     

Insight of structural,dielectric and spectroscopic characteristics of Ba0.6Sr0.4-xYbxFe12-yCoyO19 M-type hexaferrite

Ba_0.6Sr_0.4-xYb_xFe_12-yCo_yO₁₉, (0.0≤x ≤ 0.125, 0.0≤y ≤ 1.25) M-type hexaferrite were synthesized using the auto combustion sol-gel process. The synthesized samples were then sintered at 1200 °C for 5 h in a muffle furnace. XRD, FTIR, Raman, and Photoluminescence spectroscopies were used to analyse all the samples. XRD technique was used for structural examination of Ba_0.6Sr_0.4-xYb_xFe_12-yCo_yO₁₉. The XRD patterns of Yb–Co co-substituted M-type hexaferrites revealed the pure single phase of synthesized samples. Change in Yb–Co concentration influenced lattice parameters and unit cell volume. The variations in lattice constants "a" and "c" values are 5.891–5.862 and 23.180–23.317. FTIR spectroscopic data graphs revealed the formation of several absorption bands from 430 cm^?1 to 3000 cm^?1. The strain in the unit cell produced by substitution changes in Raman spectra which is also confirmed by XRD. Many 630 nm–700 nm emissions were observed in the PL spectra of Ba_0.6Sr_0.4-xYb_xFe_12-yCo_yO_19. Furthermore, a bandgap of 1.961–1.875 eV was observed for the pure sample. The substitution improves the dielectric losses and Ac conductivity. The Maxwell-Wagner theory was used to investigate the changing trends of characteristics regarding dielectric parameters. The findings show that the samples with the appropriate cationic substitution can be used in microwave and high-frequency applications.     

Structural and Magnetic Property of Co1‐xNixFe2O4 Nanoparticles Synthesized by Hydrothermal Method

The cobalt nickel ferrite (Co_1‐xNi_xFe₂O₄ x = 0–1.0) nanoparticles were synthesized by a hydrothermal method. Effects of nickel content and organic template on the microstructure and magnetic property of the nanoparticles were studied. The experimental results indicate that Ni²⁺ substitution for Co²⁺ and special synthesis technique leads to obvious change in microstructure and magnetic property of the ferrites. The ferrites show nonlinear variations in the saturation magnetization and the coercivity with nickel substitution, which are explained by shape anisotropy and supernormal cation distribution. The organic template also leads to variation in the microstructure and properties of the nanoparticles.     

Effectiveness of Ni incorporation in iron oxide crystal structure towards thermochemical CO2 splitting reaction

In this study, Ni-doped iron oxide (Ni_xFe_3−xO₄) materials were synthesized via the 1,2-epoxypropane assisted sol-gel method by varying the molar concentration of Ni from x=0.2 to 1. Sol-gel derived Ni_xFe_3−xO₄ gels were dried and the dried powder was further calcined upto 600 °C in air for 90 min. Obtained calcined Ni_xFe_3−xO₄ powders were further analyzed to determine the phase composition, crystallite size, specific surface area, pore volume, and morphology via powder X-ray diffraction (PXRD), BET surface area analysis (BET), as well as scanning and transmission electron microscopy (SEM and TEM). The obtained results in the synthesis and characterization section indicate formation of Ni_xFe_3−xO₄ nanoparticles with high specific surface area. Thermal reduction and re-oxidation of the sol-gel synthesized Ni_xFe_3−xO₄ materials were determined by using the high temperature thermogravimetry. Obtained results indicate that the amount of O₂ released during the thermal reduction step (at 1400 °C) and quantity of CO produced during the CO₂ splitting step (at 1000 °C) increases as the concentration of Ni inside the iron oxide crystal structure increases. The highest amounts of O₂ released (221.88 μmol/g) and CO produced (375.01 μmol/g) in case of NiFe₂O₄ (NF10 material).     

Nanostructured quaternary Ni1-xCuxFe2-yCeyO4 complex system: Cerium content and copper substitution dependence of cation distribution and magnetic-electric properties in spinel ferrites

Quaternary Ni_1-xCu_xFe_2-yCe_yO₄ complex nano-ferrites system with different cerium content ratio and copper substitution degree were synthesized via co-precipitation wet chemical technique. The newly obtained nanoparticles, with general formula Ni_1-xCu_xFe_2-yCe_yO₄ (where x = 0.0, 0.3, 0.6 and y = 0.00, 0.03, 0.05, 0.08 and 0.10) were heated up to 600 °C to stabilize the specific crystalline spinel structure. The limit of cerium content was quantitively determined to be around 0.08 and up to 0.10. Furthermore, the powders were pelletized in a 13 mm wide pellets and thermally treated at 950 °C. The thermal treatment affected even more the phases segregation process, as CeO₂ was identified in the sample with lowest degree of cerium insertion – 0.03. Also, a difference in color and size of pelletized samples was noticed after the 950 °C thermal treatment. The Rietveld refinement, crystal structure confirmation, morphology magnetic and electrical properties of samples have been deeply studied. The cation distribution carried out from Rietveld refinement confirms the occupancy of (Fe³⁺) on tetrahedral sites and [Ni²⁺], [Cu²⁺], [Fe³⁺] and [Ce²⁺] on octahedral sites in the crystal lattice. Preliminary information regarding the cation distribution in spinel structures were suggested by FTIR spectral results, precisely in the 650-520 cm^?1 region, as a consequence of peak shape and lack of shiftiness of M^Td – O bond. Spherical-shaped quaternary nano-ferrites of 17–28 nm were determined from FE-SEM analysis and the samples composition was confirmed by EDX analysis. Hysteresis loops shows modifications in coercivity, magnetization and magnetic remanence with Ni²⁺ and Cu²⁺ ions doping in Ni_1-xCu_xFe_2-yCe_yO₄ complex systems with typical ferrimagnetic behavior. Dielectric measurements were employed in order to determine the electrical permittivity, dielectric losses and conductivity values in a 10 Hz – 1 MHz frequency range.     

Heat generation properties in AC magnetic field for Y3Fe5O12 powder material synthesized by a reverse coprecipitation method

Ferrimagnetic Y₃Fe₅O₁₂ powder was synthesized by a reverse coprecipitation method in order to study its heat generation property in an AC magnetic field. An orthorhombic YFeO₃ phase having a small particle size (<100 nm) was obtained for the samples calcined at a low temperature. The maximum heat generation ability in an AC magnetic field was obtained for the Y₃Fe₅O₁₂ ferrite powder by calcination at 1100 °C. The heat generation ability was reduced for the samples calcined at a higher temperature. The particle growth with the formation of the cubic single phase might influence the heat generation ability. The heat generation ability and the hysteresis loss value were proportional to the cube of the magnetic field (H³), because the coercivity value of the B–H curve was proportional to the square of the amplitude of the AC magnetic field (H²). The heat generation ability (W g⁻¹) of the Y₃Fe₅O₁₂ sample sintered at 1100 °C can be expressed by the equation 2.2×10⁻⁴∙f∙H³ using the frequency (f/kHz) and the magnetic field (H/kA m⁻¹), which has the highest heat generation ability of the reported magnetic materials. The hysteresis loss value for the B–H curve agreed with the heat generation ability of the samples calcined at 1100 °C and lower temperatures.     

Y3+ composition and particle size influenced magnetic and dielectric properties of nanocrystalline Ni0.5Cu0.5YxFe2-xO4 ferrites

The rare earth Yttrium (Y³⁺) doped Ni–Cu nanoferrites (NCY ferrites) with chemical formulation, Ni_0.5Cu_0.5Y_xFe_2-xO₄ (x = 0–0.125) were prepared successfully by the sol gel route. The X-ray diffraction (XRD) of NCY ferrites revealed that a single phase of cubic spinel is created within the synthesized ferrites. The crystallite sizes obtained by XRD pattern are in the range of 51–84 nm, in good agreement with those obtained by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FSEM). The calculated lattice parameter of NCY ferrite unit cells initially decreases up to x = 0.1 and increase afterwards for x = 0.125. From FESEM and TEM micrographs, surface morphology and microstructure of NCY nanoferrites were studied. The energy dispersive X-ray spectroscopy (EDS) patterns have confirmed the stoichiometric presence of Ni, Cu, Y, O and Fe, those were used to prepare the samples. The variations in the magnetic properties with Y³⁺ compositions were investigated by obtaining the hysteresis loops of NCY ferrites. The magnetic hopping lengths L_A and L_B were calculated from XRD. The saturation magnetization, Bohr magneton number, coercivity and retentivity of the ferrites were influenced by the structural parameters like crystallite size and lattice strain. The frequency variation of dielectric constant and loss tangent exhibit space charge polarization as a phenomenon governing the dielectric behavior of the ferrites.     

Structural,spectral, dielectric and photocatalytic studies of Zr-Ni doped MnFe2O4 co-precipitated nanoparticles

In this study the Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles fabricated by co-precipitation technique were investigated. Thermo-gravimetric analysis (TGA) exhibited the annealing temperature of the nanoparticles ~990 °C. Cubic spinel structure of Mn_1–2xZr_xFe_2−yNi_yO₄ nanoparticles was confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analysis. Crystallite size was calculated by XRD data and found in the range of 32–58 nm. Photocatalytic activity of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄/graphene nanocomposites was tested by degrading methylene blue (MB) under visible light irradiation. The MB was almost completely degraded in the presence of Mn_0.92Zr_0.04Fe_1.88Ni_0.12O₄-graphene nanocomposites under visible light irradiation. Dielectric parameters were also investigated in the frequency range 1×10⁶–3×10⁹ Hz. An overall decrease in the values of dielectric constant, dielectric loss and tangent loss was observed on account of the substitution of Zr and Ni with Mn and Fe cations.     

Structure,magnetic properties and microwave absorption properties of NdFe1-xNixO3

In this paper, a high-purity NdFe_1-xNi_xO₃ perovskite-type material was prepared by a simple sol method. At the same time, adjust the substitution content of nickel to achieve the purpose of adjusting the dielectric properties and magnetic properties. According to the respective instruments, as Ni is substituted into the NdFeO₃, the crystal microstructure will change to a certain extent, and there is a certain causal relationship between the magnetic properties and the bonding. Therefore, by adding a certain amount of nickel, the dielectric properties and magnetic properties can be adjusted to a certain balance point. NdFe_1-xNi_xO₃ material has excellent microwave absorption performance. When x = 0.2, the minimum reflection loss value is ?49.32, and the corresponding impedance matching value is 1, and the effective bandwidth is 2.2 GHz when the thickness is 5.0 mm. The material that adjusts the perovskite structure by Ni element is beneficial to make the microwave absorption peak move from high frequency to low frequency, which has a wider application range and is closer to civil, commercial, military and aerospace.     

Effect of mechanochemical synthesis on the structure,magnetic and optical behavior of Ni1−xZnxFe2O4 spinel ferrites

Ni_1−xZn_xFe₂O₄ (0≤x≤1) nanocrystals were prepared by a soft mechanochemical approach. The structure and morphology were assessed via X-ray powder diffractometery (XRD), infrared spectroscopy (FTIR), Raman spectroscopy, transmission electron microscopy (TEM) and Energy dispersive spectroscopy (EDS). The magnetic characteristics have been evaluated using vibrating sample magnetometer (VSM). The optical properties were explored by diffuse reflectance UV–visible spectrophotometry (DRS). The substitution of Zn into the Ni_1−xZn_xFe₂O₄ nanocrystals increased the mean nanocrystal size from 4 to 19 nm. The FTIR and Raman spectroscopies showed that the substitution with Zn up to x=0.5 in Ni_1−xZn_xFe₂O₄ nanocrystals results in a migration of Fe ions from tetrahedral to octahedral sites, leading to an improvement of the saturation magnetization value to 33.8 emu/g. At the same time, the optical band gap decreased from 2.6 to 1.93 eV due to the increase of the Zn content from x=0 to x=1. These promising characteristics of Ni_1−xZn_xFe₂O₄ nanocrystals make them suitable for the use in the field of magnetically recoverable catalysts including those for energy applications.     

Effect of yttria substitution on structure,optical and mechanical properties of (Gd,Y)2O3–MgO nanocomposite ceramics

A citrate-nitrate combustion method was applied to synthesize fine composite Gd_2-xY_xO₃-MgO (x = 0, 0.02, 0.2, 0.3, 0.4, 0.6) nanopowders. Y₂O₃ substitution inhibited Gd₂O₃ phase transition from cubic structure to monoclinic structure during sintering, thereby stabilizing its cubic structure to room temperature. This approach led to nanocomposite ceramics with a grain size of about 190 nm and increased the transmittance to 85% over the 3–5 μm wavelength range when x = 0.3. However, the addition of Y₂O₃ weakened the mechanic properties of the nanocomposite ceramics.     

Preparation of Y3Fe5O12 Microsphere Using Bead‐Milled Nanosize Powder for Embolization Therapy Application

Y₃Fe₅O₁₂ microspheres having a 20–32 μm diameter range were prepared by a spray dryer using a bead‐milled nanosize powder. The high heat generation ability in an AC magnetic field was obtained by the bead milling of a commercial powder. The yield of the 20–32 μm microspheres was 13.5% after sifting using 20 and 32 μm sieves. The heat generation ability of the microsphere sample was almost the same as that for the bead‐milled powder because the temperature enhancement mechanism was the Néel relaxation of the superparamagnetic material. Furthermore, the heat generation ability of the Y₃Fe₅O₁₂ microsphere was improved by calcination at low temperature. The heat ability increased as a function proportional to the square of the increasing magnetic field for the noncalcined sample and the samples calcined at 600°C. For the samples calcined at 650°C or higher, the heat generation ability increased as a function proportional to the cube of the increasing magnetic field because of the particle growth to form single‐domain ferrimagnetic particles. The sample calcined at 650°C showed the maximum heat generation ability(W/g) of 2.4·f·H³, where f and H are the frequency (kHz) and magnetic field (kA/m), respectively.     

Structural,electrical, optical and dielectric properties of yttrium substituted cadmium ferrites prepared by Co-Precipitation method

The yttrium substituted cadmium ferrites having composition Cd_1-xY_xFe₂O₄ (X = 0.00, 0.125, 0.250, 0.375, 0.500) were synthesized by the co-precipitation method and sintered at 1100 °C for 6 h. Structural, morphological, electrical, optical and dielectric characteristics were explored by XRD, SEM, EDS, FTIR, I–V two probes, UV–Vis and LCR techniques.XRD results confirmed the cubic structure of spinel ferrites. A decrease in lattice constants of the prepared samples was observed with the substitution of Y ions and was attributed to the difference in ionic radii of Y³⁺ (0.95 Å) and Cd²⁺ (0.97 Å) ions. Cationic distributions, ionic radii of both tetrahedral and octahedral sites, tolerance factor, oxygen positional parameters, bond lengths, interatomic distances, positional parameters and bond length angles were calculated from XRD data. The morphology of the prepared ferrites was studied using SEM and results ratified the XRD results. EDS confirmed the presence of all inserted elements in Cd_1-xY_xFe₂O₄ composition. DC resistivity and drift mobility of soft-ferrites were found to be increased from 1.047 × 10⁸–4.822 × 10¹⁰ Ω-cm and 5.87 × 10⁻¹² – 1.045 × 10⁻¹⁴ cm²V⁻¹s⁻¹, respectively, at 523 K with yttrium content confirming the behavior of semiconductor materials. The optical band gap energy calculated from the UV–Vis pattern of the Cd_1-xY_xFe₂O₄ system was decreased from 3.6011 to 2.8153 eV. DC resistivity and optical band gaps exposed inverse relation. FTIR results revealed lower and upper-frequency absorption bands in the ranges of 419.31–417.01 cm⁻¹ and 540.95–565.70 cm⁻¹, respectively. Dielectric constant and dielectric losses were in decreasing order, while ac conductivity revealed rising behavior with increasing frequency. Results showed the potential of yttrium doped Cd nanoferrites for applications in high-frequency microwave absorbing devices.     

Magnetic doping effects on the superconductivity of Y1-xMxBa2Cu3O7-δ (M = Fe,Co, Ni)

The discovery of superconductivity in copper oxide compounds has attracted considerable attention over the past three decades. The high transition temperature (T_c) in these compounds, exhibiting proximity to an antiferromagnetic order in their phase diagrams, remains one of the main areas of research. It is believed that magnetic fluctuations provide substance for the exotic superconductivity observed in these compounds. The present study attempts to introduce Fe, Co and Ni magnetic impurities into the superconducting cuprate YBa₂Cu₃O_7-δ with the aim of exploring the T_c behavior. The solid-state synthesis method is exploited to prepare fully oxygenated Y_1-xM_xBa₂Cu₃O_7-δ (Y_1-xM_x-123) (M = Co, Fe, Ni) samples with low levels of doping (0.00000 ≤ x ≤ 0.03000). Systematic measurements are then employed to assess the synthesized samples using AC magnetic susceptibility, electrical resistivity and X-ray diffraction (XRD). The measurements revealed an increase in T_c as a result of magnetic substitution for Y. However, the study of non-magnetic dopings on the fully oxygenated Y_1-xM'_xBa₂Cu₃O_7-δ (Y_1-xM'_x-123) (M' = Ca, Sr) samples showed a decrease in T_c. Quantitative XRD analysis further suggested that the internal pressure could have minor effects on the increase in T_c. The normal state resistivity vs temperature showed a linear profile, confirming that the samples are at an optimal doping of the carrier concentration.     

Ni–Fe Catalysts Based on Perovskite-type Oxides for Dry Reforming of Methane to Syngas

LaNi_(1−x)Fe_xO₃ (x=0, 0.2, 0.4 and 0.7) perovskite-type catalysts were modified by the partial substitution of nickel by iron, aiming to increase the stability and resistance to carbon deposition during the methane dry reforming reaction. The results showed that a suitable combination of precipitation and calcination steps could result in oxides with the desired structure and with improved properties from the point of view of heterogeneous catalysis. The partial substitution of Ni by Fe in the perovskite structure resulted in decreasing rates of conversion of both reactants. However, the stability of the catalyst during the reaction was highly increased. These substituted catalysts were shown to be stable and the LaNi_0.8Fe_0.2O₃ catalyst, calcined at 800 °C for 5 h, was the most active in the reaction conditions.     

Mechanistic study of the effect of Ca–Sn co-doping on the microwave dielectric properties and magnetic properties of YIG

To investigate the crystal structure, electrical properties, and magnetic properties of Ca–Sn co-doped Y_3-xCa_xFe_5-xSn_xO₁₂ (x = 0.00–0.25 in steps of 0.05), solid-state reaction experiments, first principles calculations, and complex crystal bonding theoretical calculations were performed. The relative permittivity (ε_r) is strongly correlated with the average bond ionicity when Ca²⁺ is added. Furthermore, appropriate Sn⁴⁺ substitution significantly lowers the dielectric loss (tanδ_ε) associated with the lattice energy. The right amount of Ca–Sn co-doping can change the saturation magnetization (4πM_S) and improve the microscopic morphology of YIG, lowering the ferromagnetic resonance linewidth (ΔH) of YIG. The optimized microwave dielectric and magnetic properties are as follows: ε_r = 14.7, tanδ_ε = 4.15 × 10^?4, 4πM_S = 1680 G, and ΔH = 53 Oe for Y_2.8Ca_0.2Fe_4.8Sn_0.2O₁₂ sintered for 6 h at 1425 °C. Based on this material, a simple 3D model of a strip-line circulator with an insertion loss of less than 0.3 dB at each port and isolation greater than 20 dB in the 10–12 GHz range was developed, indicating the potential of the material for microwave high-frequency components such as circulators.     

Fe3+-substituted aluminium oxide nano-flakes: Structural,morphological, optical,and gas sensing properties

Mixed metal oxides with chemical formula Fe_xAl_2-xO₃ (where x = 0.2–1.0) (FANF) was synthesized via sol-gel auto combustion process. X-ray diffraction, field emission scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy were employed to characterize produced oxide materials. The final product FANF was sintered for 5 h at 1100 °C. The TG-DTA validated the mixed metal oxides phase evolution and steady-state temperature. The replacement of aluminium ions results in orthorhombohedral structure in mixed metal oxides (MMO). The bandgap decreased from 3.72 eV to 3.21 eV and the crystallite size decreased from 28 nm to 14 nm as the iron content increased in the sample Fe_xAl_2-xO₃ (where x = 0.2–1.0). The FT-IR confirmed no impurity peaks and the single phase with iron oxide band is near 432 cm^?1, while the aluminium oxide band is 565–600 cm^?1. Microstructural investigation shows flake-like growth, and EDS confirmed a stoichiometric ratio of MMO. Iron-substituted aluminate gas sensors detected CO, H₂S, and NO₂ at temperature ranging from 25 to 300 °C. Fe_0.6Al_1.4O₄ (F₃ANF) sensor responded 46.69% towards 100 ppm H₂S at 200 °C. Overall, the results showed that a flake-like FANF sensor can be used effectively as a H₂S gas sensor.