Development of magnetic recyclable spinel photocatalysts with enhanced sunlight-driven degradation of industrial dyes

Nanocrystalline nickel and copper-substituted zinc aluminate spinel powders (Ni_xZn_1−xAl₂O₄ and Cu_xZn_1−xAl₂O₄) with different additional ion concentrations (0 ≤ x ≤ 1) were successfully synthesized by the sol-gel auto combustion method using diethanolamine (DEA) as a fuel. The structures, chemical bonds, morphologies, composition, surface area, and optical properties including the magnetic behavior of the obtained samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer-Emmett-Teller (BET) method, UV-visible diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM). All characterization results confirmed that a single-phase spinel structure was obtained for all calcined aluminate powders with various crystallite sizes and lattice constants. The band gap energy (E_g) of all modified aluminates is in the range of 2.99-3.15 eV, which was found to be much lower than that of the pure sample (5.60 eV). These results indicate that the Ni²⁺ and Cu²⁺-substituted ZnAl₂O₄ samples could be effectively photoexcited by both the ultraviolet and visible light. Evaluation of the samples to determine the photocatalytic activity was carried out through investigation of the way the four main pollutant types decompose when irradiated by sunlight. These pollutants were rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). For all optimum samples of organic dyes, the efficiency of photocatalytic degradation achieved 96% by the end of 150 min. Furthermore, each of the modified photocatalysts could be reused and showed a high degree of stability. According to magnetic measurements, the S-shaped curve of ferrimagnetism can arise in those samples with the optimum concentration, although pure ZnAl₂O₄ exhibits diamagnetic properties. In comparison to pure ZnAl₂O₄, the modified samples exhibit high enhancement in the remanent magnetization (M_r), which indicates that it is easy to recover those magnetic photocatalyst through the use of an external magnetic field application. These findings therefore serve as a strong indication that ZnAl₂O₄ powders substituted by both Ni²⁺ and Cu²⁺ may offer the capability to serve in environmentally beneficial harvesting of solar energy.     

Influence of iron oxide substitution on the magnetic interactions in sol–gel-derived 45S5 bioactive glass–ceramics

Magnetic interactions in sol–gel-derived bioactive magnetic glass–ceramics (MGCs) with compositions of (45 − x)SiO₂·24.5CaO·24.5Na₂O·6P₂O₅ xFe₂O₃ (2 ≤ x ≥ 15 wt.%) have been investigated using electron paramagnetic resonance (EPR), and temperature-dependent magnetic susceptibility and magnetization (M–T) techniques. EPR spectra of the MGC samples revealed strong composition dependence in the intensity and linewidth of resonance absorptions at g ≈ 2.0 and g ≈ 4.3. EPR linewidth analysis showed the dominance of dipole–dipole interaction in MGC samples with iron oxide content ≤4 wt.% and a crossover to super-exchange type interaction in samples with higher iron oxide content. Composition-dependent magnetic interaction in these MGC could be related to Fe²⁺ and Fe³⁺ ion concentrations using high-temperature magnetic susceptibility studies. Zero-field cooled and field cooled M–T curves indicate different magnetic behavior for MGC samples with x ≤ 6 and x ≥ 8 wt.% iron oxide. Although the former show weak magnetic behavior, the latter exhibit superparamagnetic behavior which could be correlated with the percentage of magnetic phases present in each sample. These studies reveal composition-dependent variation in dipolar and super-exchange type interaction in the samples which could help in assessing these MGC for biomedical applications.     

Molten salt synthesis of zinc aluminate powder

ZnAl₂O₄ powder was synthesised by reacting equimolar ZnO and Al₂O₃ powders in alkaline chlorides (LiCl, NaCl or KCl). Formation of ZnAl₂O₄ started at about 700 °C in LiCl and 800 °C in NaCl and KCl. With increasing temperature, the amounts of ZnAl₂O₄ in the resultant powders increased with a concomitant decrease of ZnO and Al₂O₃. ZnAl₂O₄ powder was obtained by water-washing the samples heated for 3 h at 1000 °C (LiCl) or 1050 °C (NaCl and KCl). ZnAl₂O₄ formed in situ on Al₂O₃ grains from the surface inwards. The synthesised ZnAl₂O₄ grains retained the size and morphology of the original Al₂O₃ powders, indicating that a template formation mechanism dominated formation of ZnAl₂O₄ by molten salt synthesis.     

Microwave-assisted solution combustion synthesis of Fe3O4 powders

Magnetite (Fe₃O₄) powders were synthesized by solution combustion method at different fuel to oxidant ratios (ϕ = 0.5, 0.75, 1 and 1.5) using conventional and microwave ignition. The ignition method and fuel content affected the phase evolution, microstructure and magnetic properties of Fe₃O₄ powders as characterized by X-ray diffractometry, infrared spectroscopy, N₂ adsorption–desorption, electron microscopy and vibrating sample magnetometry techniques. Single phase Fe₃O₄ powders were only obtained using conventional ignition at ϕ value of 1, while the impurity phases such as α-Fe₂O₃ and FeO together with Fe₃O₄ phase were formed by microwave ignition. The bulky microstructure of conventionally combusted powders with specific surface area of 71.5 m²/g was transformed to disintegrated structure (76.5 m²/g) by microwave heating. The microwave combusted powders showed the highest saturation magnetization of 86.5 emu/g at ϕ value of 0.5 and the lower coercivity than that of conventionally combusted powders at all ϕ values, due to their larger particles.     

Origin of Violet‐Blue Emission in Ti‐Doped Gahnite

ZnAl₂O₄ doped with Ti⁴⁺ (2%) was synthesized by the hydrothermal method at 220°C at pressure of 25 bars. An average grain size of the as‐prepared sample was 3 nm, the samples with biggest grain size were obtained after annealing at 300°C, 500°C, 600°C, 700°C, and 900°C, diameter of the latter was about 33 nm. IR spectroscopy indicated that ZnAl₂O₄ was partially inverted. The degree of the inversion decreases with increase in the annealing temperature but increases with increasing Ti⁴⁺ content. Absorption and emission spectra as well as emission decay profiles were recorded at 300 and 77 K. The observed spectra are due to charge‐transfer O^2??Ti⁴⁺ transitions. Color of the emission depends on the nanocrystal size and with increase in its diameter changes from violet to blue, accordingly the absorption bands exhibit redshift. The calculations based on Density Functional Theory confirmed the experimental results. 3d electrons of titanium ions form the bottom of the ZnAl₂O₄:Ti⁴⁺ conduction band, oxygen, aluminum or zinc vacancies create additional levels in the gahnite energy band gap. It was also found that in ZnAl₂O₄ aluminum or zinc vacancy induces magnetism with relatively high magnetic moment close to 1 μ_B per vacancy.     

Effects of calcination temperature on structure and magnetic properties of pure FeCo2O4 powders

A series of FeCo₂O₄ powders was initially synthesized using a hydrothermal method and subsequently calcined at various temperatures to produce the final product. Pure phase FeCo₂O₄ powders can only be formed in the temperature range of 950–1050 °C. In this work, we study the cation occupation, cation valence, bond length and bond angle changes of the pure phase FeCo₂O₄ powders formed in such a narrow temperature range. Octahedral lattice distortion in the pure phase FeCo₂O₄ samples has been observed. More tetrahedral Fe³⁺ and octahedral Co²⁺ are excited and exchanged their sites as the calcination temperature increases from 950 °C to 1000 °C, and part of Co³⁺ ions are reduced to Co²⁺ in the sample calcined at 1050 °C. The structure of the sample calcined at 1000 °C is close to that of the ideal FeCo₂O₄ spinel. Magnetic measurements show that ferrimagnetism and anti-ferromagnetism coexist in the pure phase FeCo₂O₄ samples. Interaction changes between ferrimagnetism and antiferromagnetism caused by the structural changes of the samples have been studied. Due to the pinning of the local anti-ferromagnetism to ferrimagnetism in the sample, the sample shows a Barkhausen jump below 150 K. As the measurement temperature increases further, the system enters into a reentrant spin glass state.     

Sol-gel auto-combustion synthesis of Ba–Sr hexaferrite ceramic powders

We report the mechanism involved in sol-gel auto-combustion synthesis of Ba–Sr-hexaferrite (Ba_1-xSr_xFe₁₂O₁₉; x = 0, 0.25, 0.5, 0.75 and 1, BSFO) ceramic powders through the analysis of the phases evolved during annealing of the as-synthesized powders, along with their structure and morphological studies. The XRD patterns of the as-synthesized samples indicate the formation of barium/strontium monoferrite ((Ba/Sr)Fe₂O₄) and maghemite (γ-Fe₂O₃) phases along with a minute amount of hematite (α-Fe₂O₃) phase. Annealing of these samples facilitates formation of BSFO phase through the solid state reaction between BaFe₂O₄ and γ-Fe₂O₃ phase. Interestingly, after annealing the samples with x = 0, 0.5 and 1, at 1000 °C for 2 h, we observed that phase pure Ba–Sr hexaferrite structure forms, but for samples with x = 0.25 and 0.75, high amount of hematite (α-Fe₂O₃) phase is observed, especially for x = 0.75. The reason associated with this could be the large difference between the ionic radii of Ba²⁺ and Sr²⁺ ions occupying the oxygen site. Furthermore, our study on annealing dependent phase evolution confirms that, this difference in ionic radii forbids the formation of a single phase Ba–Sr hexaferrite. The growth of clear hexagonal-shaped plate-like particles with varied particle sizes was observed for all the samples. The particle size variation may be due to the influence of the ionic radii difference on the sinterability of the samples. Our study provides a better understanding of synthesis mechanism of Ba–Sr hexaferrite samples.     

Development of bifunctional Mo doped ZnAl2O4 spinel nanorods array directly grown on carbon fiber for supercapacitor and OER application

Electrochemical energy storage and water splitting strategies may be greatly improved with proper structural design and doping techniques. In the present study, molybdenum-doped ZnAl₂O₄ loaded on carbon fiber (Mo–ZnAl₂O₄/CF) was fabricated via a simple hydrothermal synthetic approach. Due to its unique hierarchical nanostructures and enhanced electrical, structural topologies, Mo-doped ZnAl₂O₄ demonstrates exceptional supercapacitor performance and electrocatalytic oxygen evolution reaction activity. The Mo-doped ZnAl₂O₄ electrode material exhibited 1477.63 F g^?1 specific capacitance, 46.57 Wh Kg^?1 specific energy and specific power of 476.4 W kg^?1 at 1 A g^?1. After 5000 cycles, the pseudo supercapacitor retains 97.46% of its capacitance and displays stable behavior over 50 h. During the OER reaction, the Mo–ZnAl₂O₄/CF as an electrocatalyst rapidly self-reconstructs, resulting in many oxygen vacancies, and causes a lower 38 mV dec^?1 Tafel slope and overpotential potential of 255 mV to achieved 10 mA cm^?2 current flow and responsible for the excellent stability of the electrocatalyst. These findings suggest that multifunctional materials based electrode for electrical energy conversion and storage become more efficient and stable by using Mo for doping to generate porous hierarchical structures and local amorphous phases.     

Molten Salt Synthesis of Bismuth Ferrite Nano‐ and Microcrystals and their Structural Characterization

Bismuth ferrite nano‐ and microcrystals were prepared by a facile molten salt technique in two kinds of molten‐salt‐based systems (NaCl–KCl and NaCl–Na₂SO₄). In the NaCl–KCl salt system, a systematic study indicating the effects of process parameters (e.g., calcination temperature, holding time as well as the molten salt ratios) on the bismuth ferrite formation mechanism and structural characteristics is reported. The results show that almost pure phase BiFeO₃ powders with minimum impurity phase of Bi₂Fe₄O₉ were synthesized at temperatures of 700°C–800°C, whereas high calcination temperature (e.g., 900°C) resulted in the formation of almost pure phase Bi₂Fe₄O₉ powders. The prolonged holding time increased the particle size via the Ostwald ripening mechanism; however, there was little effect on the particle morphology. Similar phenomenon occurred as increasing the molten salt ratios. In the NaCl–Na₂SO₄ salt systems, it is found that low NP‐9 (nonylphenyl ether, NP‐9) surfactant content (0–5 mL) led to the formation of almost pure phase BiFeO₃ powders, whereas high NP‐9 surfactant content (e.g., 20 mL) resulted in pure phase Bi₂Fe₄O₉ powders. The average particle size of the BiFeO₃ powders was decreased as increasing the NP‐9 surfactant content, whereas their morphologies did not change significantly. Because of the simplicity and versatility of the approach used, it is expected that this methodology can be generalized to the large‐scale preparation of other important transitional metal oxides with controllable sizes and shapes.     

Improved sinterability and microwave dielectric properties of [Zn0.5Ti0.5]3+-doped ZnAl2O4 spinel solid solution

Low-permittivity ZnAl_2-x(Zn_0.5Ti_0.5)_xO₄ ceramics were synthesized via conventional solid-state reaction method. A pure ZnAl₂O₄ solid-state solution with an Fd-3m space group was achieved at x ≤ 0.1. Results showed that partial substitution of [Zn_0.5Ti_0.5]³⁺ for Al³⁺ effectively lowered the sintering temperature of the ZnAl₂O₄ ceramics and remarkably increased the quality factor (Q × f) values. Optimum microwave dielectric properties (ε_r = 9.1, Q × f = 115,800 GHz and τ_f = −78 ppm/°C) were obtained in the sample with x = 0.1 sintered at 1400°C in oxygen atmosphere for 10 h. The temperature used for the sample was approximately 250°C lower than the sintering temperature of conventional ZnAl₂O₄ ceramics.     

Investigation of g-C3N4/ZnAl2O4 and ZnO/ZnAl2O4 nanocomposites: From synthesis to photocatalytic activity of pollutant dye model

The fabrication of nanocomposite photocatalytsts with excellent photocatalytic activity is an important step in the improved degradation of organic dyes. A series of nanocomposite photocatalysts was synthesized with g-C₃N₄ and ZnO loading contents of 10, 20 and 30%. The nanocomposites were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The optical band gaps of g-C₃N₄, ZnO and ZnAl₂O₄ were about 2.79, 3.21 and 3.55 eV, respectively. Methylene blue (MB) was degraded over the prepared photocatalysts under UV irradiation. Photocatalytic activity was about 9.1 and 9.6 times higher, respectively, on 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts than on pure ZnAl₂O₄ spinel powders. Recycling experiments showed that 20%g-C₃N₄/ZnAl₂O₄ and 20%ZnO/ZnAl₂O₄ nanocomposite photocatalysts exhibited good stability after five cycles of use.     

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.     

Synthesis,optical, and magnetic properties of six-layered Aurivillius bismuth ferrititanate

This work reports on the preparation, structure, photochemical, and magnetic properties of six-layered Aurivillius bismuth ferrititanates, that is, Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles. The samples were prepared through the modified citrate complexation and precursor film process. The XRD Rietveld refinements were conducted to study the phase formations and crystal structure. The morphological and chemical component characteristics were investigated using SEM, TEM, and EDX analyses. Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles present an indirect allowed transitions with band energies of 2.04, 2.03, and 2.02 eV, respectively. The hybridized (O2p+Fet_2g+Bi6s) formed the valence band (VB) and electronic components of (Ti–3d+Fe–e_g) formed the conduction band (CB) of this six-layered Aurivillius bismuth ferrititanate. The three samples showed efficient photocatalytic degradation of Rhodamine B (RhB) dyes with the excitation wavelength λ > 420 nm. The optical absorption, photodegradation, and magnetic abilities were improved through microstructural modification on “B” site via partial substitution of Mg²⁺ and Nb⁵⁺ for Ti⁴⁺. The photocatalytic results were discussed based on the layer structure and multivalent Fe ions. Fe^3+/2+ in the perovskite slabs (Bi₅Fe₃Ti₃O₁₉)²⁻ could act as the catalytic mediators in the photocatalysis process. As a photocatalyst, Aurivillius Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticle is advantageous due to its photocatalytic and magnetically recoverable abilities.     

Synthesis and characterization of Sr2+ and Gd3+ doped magnetite nanoparticles for magnetic hyperthermia and drug delivery application

Commendable efforts have been gingered towards the fight against cancer. Nevertheless, it remains a major public health concern due to its predominant cause of death globally. Given this, we synthesized two different nanoparticles, Sr²⁺ and Gd³⁺ doped magnetite for magnetic hyperthermia and drug delivery application. Based on the characterization, the diffractogram shows that only one phase related to magnetite with a crystallite size of 10 nm was formed. TEM images revealed nanoparticles of spherical shapes of approximately 12 nm. There is no difference in magnetic saturation of the as-received synthesized samples (Fe₃O₄@Sr and Fe₃O₄@Gd), while the BET-specific surface area of Fe₃O₄@Gd is 8 m² g⁻¹ higher than Fe₃O₄@Sr. The heat generation in alternating magnetic field (the magnetic hyperthermia) of Fe₃O₄@Sr functionalized with citric acid and loaded with 5- fluorouracil (Fe₃O₄@Sr@CA@5-flu) is slower than Fe₃O₄@Gd@CA@5-flu. The specific absorption rate (SAR) of Fe₃O₄@Gd@CA@5-flu, 112.0 ± 10.4 W g⁻¹ was found to be higher than that of Fe₃O₄@Sr@CA@5-flu. The thermogram shows that 11% of the drug was successfully loaded on Fe₃O₄@Gd@CA@5-flu. The release of the antitumor drug by the synthesized nanoparticle drug carriers for ovarian cancer (SKOV-3 cells) therapy showed that more than 50% of the cancer cell’s viability was reduced after 72 h of incubation. The synthesized nanoparticles demonstrated a promising drug carrier for the treatment of SKOV-3 cells.     

Formation Behavior and High Electrical Conductivity of Metastable Lithium Iron Silicate Crystals in Rapid Quenching of Li2O–Fe2O3–SiO2 Melts

The formation behavior of spinel‐type LiFeSiO₄ crystals in the quenching of melts in the Li₂O–Fe₂O₃–SiO₂ system was examined. It was found that high quenching rates of 10³ ~ 10⁶ K/min are favorable for the formation of LiFeSiO₄ crystals. The rapid quenched samples showed high electrical conductivities of the order of 10^?2–10^?4 S/cm at room temperature and low activation energy for conduction of 0.1–0.2 eV. Both valences of Fe²⁺ and Fe³⁺ were present in the melt‐quenched samples, and rapid‐quenched samples showed ferrimagnetism. It is proposed that the chemical composition of LiFeSiO₄ formed in the rapid quenching of melts would be spinel‐type Li_1 + xFe³⁺_1 ? xFe²⁺_xSiO₄. Because the Li_1 + xFe³⁺_1 ? xFe²⁺_xSiO₄ crystalline phases are metastable, the rapid quenching technique is necessary for their synthesis. The effects of quenching rate and composition on the formation of spinel‐type LiFeSiO₄ and on the electrical conductivity of quenched samples were discussed.     

Impact of rare earth europium (RE-Eu3+) ions substitution on microstructural,optical and magnetic properties of CoFe2−xEuxO4 nanosystems

In this study, pure cobalt ferrite (CoFe₂O₄) nanoparticles and europium doped CoFe₂O₄ (CoFe_2−xEu_xO₄; x = 0.1, 0.2, 0.3) nanoparticles were synthesized by the precipitation and hydrothermal approach. The impact of replacing trivalent iron (Fe³⁺) ions by trivalent rare earth europium (RE-Eu³⁺) ions on the microstructure, optical and magnetic properties of the produced CoFe₂O₄ nanoparticles was studied. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra exposed the consistency of a single cubic phase with the evidence of Eu₂O₃ phases for x ≥ 0.2. FTIR transmittance spectra showed that, the all investigated samples have three characteristic metal-oxygen bond vibrations corresponding to octahedral B-site (υ₁ and υ₂) and tetrahedral A-site (υ₃) around 415 cm⁻¹, 470 cm⁻¹ and 600 cm⁻¹ respectively. XRD and energy dispersive X-ray spectroscopy studies affirmed the integration of RE-Eu³⁺ ions within CoFe₂O₄ host lattice and decrease of average crystals size from 13.7 nm to 4.7 nm. Transmission electron microscopy (TEM) analysis showed the crucial role played by RE-Eu³⁺ added to CoFe₂O₄ in reducing the particle size below 5 nm in agreement with XRD analysis. High resolution-TEM (HR-TEM) analysis showed that the as-synthesized spinel ferrite, i.e., CoFe_2−xEu_xO₄, nanoparticles are single-crystalline with no visible defects. In addition, the HR-TEM results showed that pure and doped CoFe₂O₄ have well-resolved lattice fringes and their interplanar spacings matches that obtained by XRD analysis. Magnetic properties investigated by the vibrating sample magnetometer technique illustrated transformation of magnetic state from ferromagnetic to superparamagnetic at 300 K resulting in introducing RE-Eu³⁺ in CoFe₂O₄ lattice. At low temperature (~5 K) the magnetic order was ferromagnetic for both pure and doped CoFe₂O₄ samples. Substitution of Fe³⁺ ions in CoFe₂O₄ nanoparticles with RE-Eu³⁺ ions optimizes the sample nanocrystals size, cation distribution and magnetic properties for many applications.     

Mechanical properties and translucency of a multi-layered zirconia with color gradient for dental applications

In this work, the properties of yttria-stabilized zirconia-based ceramics, Y-TZP containing Fe₂O₃ as coloring agent were evaluated. Nanoparticled powder of 3Y-TZP (ZrO₂ - 3 mol.% Y₂O₃) doped with different amounts of Fe₂O₃ (0.002–0.136 wt%) were compacted into monolithical or multilayered samples and sintered at 1475 °C - 2 h. The samples were characterized by X-ray diffraction analysis (XRD), relative density, scanning electron microscope (SEM). Hardness and fracture toughness in the color interface were investigated using the Vickers indentation method and the biaxial flexural strength was determined by the piston on 3 balls method (P–3B). Furthermore, optical parameters were measured using spectrophotometry in regard to sample thickness and Fe₂O₃ content. The results indicated a good adhesion between layers, proven by indentation cracks randomly growing between different regions, because the powders used produced very similar morphological characteristics. The different amounts of Fe₂O₃ studied in this work did not interfere in densification, phase composition, or microstructure of the sintered ceramics. The fracture toughness and flexural strength did not significantly change due to the addition of Fe₂O₃, presenting values close to 7 MPa m^1/2 and 1120–1150 MPa, respectively, in all studied compositions. On the other hand, increasing Fe₂O₃ contents lead to an increase in the hardness of the material (1280–1330 H V), and higher contrast ratios (CR) with a consequent loss of translucency. Color variation (ΔE) depended also on the thickness of the material.     

The effect of Fe2+ state in electrical property variations of Sn‐doped hematite powders

The structural, electrical, and chemical properties of Sn‐doped Fe₂O₃ powders were investigated. Various quantities of Sn‐doped Fe₂O₃ powders were synthesized using solid‐state reactions. Rietveld analysis for the powders that were doped below 2% revealed a phase‐pure Sn‐doped Fe₂O₃ structure (i.e., identical to Fe₂O₃ structure). Alternatively, the analysis for the powders that were doped more than 3% exhibited secondary phase. The unit cell volume and electrical conductivity of the phase‐pure samples increased with an increase in the doping concentration. X‐ray photoelectron spectroscopy measurements showed an increased Fe²⁺ state with the increase in Sn doping concentration. Therefore, the improved electrical conductivity and unit cell volume with the increase in doping concentration of the phase‐pure powders might be related to the increased Fe²⁺ state.     

Fabrication of graphene nanosheet (GNS)–Fe3O4 hybrids and GNS–Fe3O4/syndiotactic polystyrene composites with high dielectric permittivity

Graphene nanosheet–Fe₃O₄ (GNS–Fe₃O₄) hybrids were obtained by a one-step solvothermal reduction of iron (III) acetylacetonate [Fe(acac)₃] and graphene oxide (GO) simultaneously, which had several advantages: (1) the Fe₃O₄ nanoparticles were firmly anchored on GNS surface even after mild ultrasonication; (2) the loading amount of Fe₃O₄ nanoparticles could be effectively controlled by changing the initial feeding weight ratio of Fe(acac)₃ to GO; (3) the Fe₃O₄ nanoparticles were homogeneously distributed on the GNS surface without much aggregation. Composites based on syndiotactic polystyrene (sPS) and GNS–Fe₃O₄ were prepared by a solution-blending method and the electric and dielectric properties of the resultant GNS–Fe₃O₄/sPS composites were investigated. The percolation threshold of GNS–Fe₃O₄ in the sPS matrix was determined to be 9.41 vol.%. Slightly above the percolation threshold with 9.59 vol.% of GNS–Fe₃O₄, the GNS–Fe₃O₄/sPS composite showed a high dielectric permittivity of 123 at 1000 Hz, which was 42 times higher than that of pure sPS. The AC electrical conductivity at 1000 Hz increased from 3.6 × 10⁻¹⁰ S/m for pure sPS to 2.82 × 10⁻⁴ S/m for GNS–Fe₃O₄/sPS composite containing 10.69 vol.% of GNS–Fe₃O₄, showing an obvious insulator-semiconductor transition.     

Investigations of Structural and Magnetic Properties of Nanostructured Ni0.5+xZn0.5‐xFe2O4 Magnetic Feeders for CSEM Application

Marine CSEM is a new technique for detection of deep target hydrocarbons. Aluminum EM antenna was developed, and nanostructured NiZn magnetic feeders were used to increase the field strength from EM antenna for deep hydrocarbons. The doping of Ni²⁺ was aimed at the optimization of initial permeability and magnetic losses. Ni_0.5+xZn_0.5‐xFe₂O₄ (x = 0.3) samples sintered at 950°C presented highest initial permeability (106.23) and low magnetic loss (0.0002) as compared to other samples. Due to better magnetic properties, Ni_0.5+xZn_0.5‐xFe₂O₄ (x = 0.3) samples were used as magnetic feeders for EM antenna. Magnitude of EM waves from the antenna increased up to 186%.