Gas-liquid detonation synthesis of CNTs@Fe/Fe3C composites and their application as electrode materials for double-layer capacitors

Abstract

The carbon nanotubes doping with Fe and Fe₃C nanocrystal (CNTs@Fe/Fe₃C) are successfully synthesized by the gas-liquid detonation (GLD) decomposition of CH₄, O₂, C₁₀H₁₀Fe and C₁₀H₈. The composition and structural properties of the as-obtained composites were investigated by XRD, TEM, XPS and Raman spectroscopy. The obtained composites were also applied to the electric double-layer capacitor. The results showed that the specific capacitance of CNTs@Fe/Fe₃C can reach 125?F·g^?1 at the current density of 100?mA·g^?1 and after 10000 cycles the capacitance retention is 93.1% at a current density of 2?A·g^?1.     

Modulation of Inverse Spinel Fe3O4 by Phosphorus Doping as an Industrially Promising Electrocatalyst for Hydrogen Evolution

Fe‐based oxides have been seldom reported as electrocatalysts for the hydrogen evolution reaction (HER), limited by their weak intrinsic activity and conductivity. Herein, phosphorus doping modulation is used to construct inverse spinel P‐Fe₃O₄ with dual active sites supported on iron foam (P‐Fe₃O₄/IF) for alkaline HER with an extremely low overpotential of 138 mV at 100 mA cm^?2. The obtained inverse spinel Fe–O–P derived from controllable phosphorization can provide an octahedral Fe site and O atom, which bring about the unusual dissociation mechanisms of two water molecules to greatly accelerate the proton supply in alkaline media. Meanwhile, the ΔG_H of the P atom in Fe–O–P as an active site is theoretically calculated to be 0.01 eV. Notably, the NiFe LDH/IF⁽⁺⁾||P‐Fe₃O₄/IF^(?) couple achieves an onset potential of 1.47 V (vs RHE) for overall water splitting, with excellent stability for more than 1000 h at a current density of 1000 mA cm^?2, and even for 25 000 s at 10 000 mA cm^?2 in 6.0 m KOH at 60 °C. The excellent catalyst stability and low‐cost merits of P‐Fe₃O₄/IF may hold promise for industrial hydrogen production. This work may reveal a new design strategy of earth‐abundant materials for large‐scale water splitting.     

Synthesis and characterization of Bi2MoO6/MIL-101(Fe) as a novel composite with enhanced photocatalytic performance: Effect of water matrix and reaction mechanism

The integration of Bi₂MoO₆ with MIL-101(Fe) as a novel structure enhanced photocatalytic activity for RhB degradation. Bi₂MoO₆/MIL-101(Fe) composites were synthesized via the solvothermal procedure and characterized by XRD, EDX, FE-SEM, TEM, FT-IR, BET, TGA, UV–vis DRS, and PL. The optimal molar ratio Bi₂MoO₆:MIL-101(Fe) equal to 1:1 showed better photocatalytic activity than Bi₂MoO₆ and MIL-101(Fe) and other heterostructure composites. The effect of pH (5–9), reaction time (60–120 min), catalyst concentration (0.1–0.5 g/L), and dye concentration (10–20 ppm) were investigated on the removal performance of RhB by using central composite face-centered (CCF). In the optimal process factors where the [Catalyst]:0.4 g/L, [RhB]:20 ppm, pH: 6.5, irradiation time: 120 min, the RhB and TOC removal efficiency were 85% and 84.2%, respectively. The holes and superoxide radicals played a major role in the degradation of RhB. The addition of salt (NaCl, Na₂SO₄, and NaHCO₃) at different concentrations (100, 200, 400, and 800 ppm) revealed that the salts have an inhibitory role in the photocatalytic performance. At low concentrations of 100 ppm, the salts had a negative effect on removal efficiency (k_{Pure water} = 0.0155 min^?1, k_NaCl = 0.0075 min^?1, k_Na2SO4 = 0.0132 min^?1, k_NaHCO3 = 0.006 min^?1). Increasing the salt concentration to 800 ppm caused improved efficiency for NaCl (k_NaCl = 0.0141 min^?1), while for Na₂SO₄ this trend was decreasing (k_Na2SO4 = 0.011 min^?1), and for NaHCO₃ sharply diminished (k_NaHCO3 = 0.0026 min^?1).     

Fabrication of Fe3O4 Dots Embedded in 3D Honeycomb‐Like Carbon Based on Metallo–Organic Molecule with Superior Lithium Storage Performance

A novel metallo–organic molecule, ferrocene, is selected as building block to construct Fe₃O₄ dots embedded in 3D honeycomb‐like carbon (Fe₃O₄ dots/3DHC) by using SiO₂ nanospheres as template. Unlike previously used inorganic Fe₃O₄ sources, ferrocene simultaneously contains organic cyclopentadienyl groups and inorganic Fe atoms, which can be converted to carbon and Fe₃O₄, respectively. Atomic‐scale Fe distribution in started building block leads to the formation of ultrasmall Fe₃O₄ dots (≈3 nm). In addition, by well controlling the feed amount of ferrocene, Fe₃O₄ dots/3DHC with well‐defined honeycomb‐like meso/macropore structure and ultrathin carbon wall can be obtained. Owing to unique structural features, Fe₃O₄ dots/3DHC presents impressive lithium storage performance. The initial discharge and reversible capacities can reach 2047 and 1280 mAh g^?1 at 0.05 A g^?1. With increasing the current density to 1 and 3 A g^?1, remarkable capacities of 963 and 731 mAh g^?1 remain. Moreover, Fe₃O₄ dots/3DHC also has superior cycling stability, after a long‐term charge/discharge for 200 times, a high capacity of 1082 mAh g^?1 can be maintained (80% against the capacity of the 2nd cycle).     

Magnetic properties of the mixed oxides Sr0.9La0.1Fe0.9Cd0.1O3 − δ and Sr0.75La0.75Fe0.75Cd0.75O4 − δ

We have found that the 77-K magnetization per formula unit of the SrFeO_{3 ? δ} ferrite, Sr_0.9La_0.1Fe_0.9Cd_0.1O_{3 ? δ} and Sr_0.75La_0.75Fe_0.75Cd_0.75O_{4 ? δ} mixed oxides, and SrLaFeO₄ compound, calculated per mole of Fe ions, is 0.114μ_B, 0.024μ_B, 5 × 10^?3 μ_B, and 4.3 × 10^?2 μ_B, respectively. The resultant effective magnetic moment of the Fe³⁺ and Fe⁴⁺ ions $(\mu _{effFe^{3 + } ,Fe^{4 + } } )$ in the Sr_0.9La_0.1Fe_0.9Cd_0.1O_{3 ? δ} solid solution in the temperature range 520–850 K is 3.61μ_B, and $\mu _{effFe^{3 + } ,Fe^{4 + } } $ in Sr_0.75La_0.75Fe_0.75Cd_0.75O_{4 ? δ} and SrLaFeO₄ in the temperature ranges 350–600 and 100–550 K is 5.89μ_B and 5.70μ_B, respectively.     

Hierarchical 3D Cobalt‐Doped Fe3O4 Nanospheres@NG Hybrid as an Advanced Anode Material for High‐Performance Asymmetric Supercapacitors

Hierarchical nanostructure, high electrical conductivity, extraordinary specific surface area, and unique porous architecture are essential properties in energy storage and conversion studies. A new type of hierarchical 3D cobalt encapsulated Fe₃O₄ nanosphere is successfully developed on N‐graphene sheet (Co?Fe₃O₄ NS@NG) hybrid with unique nanostructure by simple, scalable, and efficient solvothermal technique. When applied as an electrode material for supercapacitors, hierarchical Co?Fe₃O₄ NS@NG hybrid shows an ultrahigh specific capacitance (775 F g^?1 at a current density of 1 A g^?1) with exceptional rate capability (475 F g^?1 at current density of 50 A g^?1), and admirable cycling performance (97.1% capacitance retention after 10 000 cycles). Furthermore, the fabricated Co?Fe₃O₄ NS@NG//CoMnO₃@NG asymmetric supercapacitor (ASC) device exhibits a high energy density of 89.1 Wh kg^?1 at power density of 0.901 kW kg^?1, and outstanding cycling performance (89.3% capacitance retention after 10 000 cycles). Such eminent electrochemical properties of the Co?Fe₃O₄ NS@NG are due to the high electrical conductivity, ultrahigh surface area, and unique porous architecture. This research first proposes hierarchical Co?Fe₃O₄ NS@NG hybrid as an ultrafast charge?discharge anode material for the ASC device, that holds great potential for the development of high‐performance energy storage devices.     

Chemical and structural properties of the system Fe2O3-In2O3

The system Fe₂O₃-In₂O₃ was studied using X-ray diffraction,⁵⁷Fe Mössbauer spectroscopy and infrared spectroscopy. The samples were prepared by chemical coprecipitation and thermal treatment of the hydroxide coprecipitates. For samples heated at 600 °C, a phase, α- (Fe_1?x In _x )₂O₃, isostructural with α-Fe₂O₃, exists for 0?x?0.8, and a phase C-(Fe_1?x In _x )₂O₃, isostructural with cubic In₂O₃, exists for 0.3?x?/1. In the two-phase region these two phases are poorly crystallized. An amorphous phase is also observed for 0.3?x?0.7. For samples heated at 900 °C the two-phase region is wider and exists for 0.1?x?0.8 with the two phases well crystallized. In these samples an amorphous phase is not observed.⁵⁷Fe Mössbauer spectroscopy of samples prepared at 600 °C indicated a general tendency of the broadening of spectral lines and the decrease of numerical values of the hyperfine magnetic field (HMF) with increasing molar fraction In₂O₃ in the system Fe₂O₃-In₂O₃. The samples prepared at 900 °C, in the two-phase region, are characterized by a constant HMF value of 510 kOe at room temperature. Infrared spectroscopy was also used to follow the changes in the infrared spectra of the system Fe₂O₃-In₂O₃ with gradual increase of molar fraction of In₂O₃. A correlation between X-ray diffraction, Mössbauer spectroscopic and infrared spectroscopic results was obtained.     

Polyamido amine (PAMAM)-grafted magnetic nanotubes as emerging platforms for the delivery and sustained release of silibinin

This work reports the synthesis of surface-modified iron oxide magnetic nanotubes (Fe₃O₄NT) with poly(amido amine) dendrimers of the third generation (PAMAM-G3) as novel nanomaterials for potential drug-delivery applications. Fe₃O₄NT were obtained by reduction of α-Fe₂O₃ nanotubes, which were synthesized following a hydrothermal strategy using SO₄ ^2?/H₂PO₄ ^? to control the size and morphology of the prepared materials. Fe₃O₄NT were further functionalized with PAMAM-G3 moieties using a silane coupling agent. Pristine and PAMAM-modified Fe₃O₄NT were characterized through TEM, FTIR, XRD, N₂ adsorption–desorption isotherms and VSM measurements, which confirmed the nanotubular morphology and magnetic behavior for both systems, and TGA analyses, which revealed a PAMAM grafting percentage of 16.8%. The effect of PAMAM conjugation on the adsorption and release properties of Fe₃O₄NT was examined using silibinin as model poorly soluble drug compound. Our results revealed that PAMAM grafting increased the maximum amount of adsorbed drug from 675 mg g^?1 in pristine Fe₃O₄NT to 825 mg g^?1 in PAMAM-Fe₃O₄NT. These quantities exceed by far the drug-loading capacity of other pristine and PAMAM-modified nanotubular systems, which constitutes a relevant outcome for the present study.     

Mechanism of Np(VI) oxidation with ozone in alkaline solutions

Bubbling of an ozone-oxygen mixture containing 0.1?C0.5 vol % O₃ at a rate of 15?C20 l h^?1 through 13 ml of a 2 × 10^?5?1 × 10^?4 M solution of Np(VI) in 0.1 and 1 M LiOH leads to the formation of Np(VII). The initial rate increases approximately in proportion to [Np(VI)] and [O ₃ ^gas ]^0.5. Up to 80% of Np(VI) is oxidized at maximum. At the O₃ concentration in the gas phase increased to 1?C4 vol %, Np(VI) is oxidized completely. Under the same conditions, Np(VI) in a concentration of (1?C5) × 10^?3 M is oxidized to almost 100%. Analysis of published data and additional experiments on the reaction of O₃ with Np(VI) ions in LiOH solutions allow a conclusion that the ozonation involves the reactions O₃ + OH^? = HO ₂ ^? + O₂, O₃ + HO ₂ ^? + OH^? = O ₃ ^? + O ₂ ^? + H₂O, and O₃ + O ₂ ^? = O ₃ ^? + O₂, followed by O ₃ ^? + NpO₂(OH) ₄ ^2? = O₂ + NpO₄(OH) ₂ ^3? + H₂O. In addition, HO ₂ ^? reduces Np(VII) and Np(VI) and reacts with O ₃ ^? . Certain contribution is made by the reaction Np(VI) + O₃ = Np(VII) + O ₃ ^? . The dependence of the Np(VII) accumulation rate on [O ₃ ^gas ]^0.5 was interpreted in terms of the concept of a heterogeneous-catalytic process.     

Heterovalent cation substitutions in the layered compound YBaCuFeO<Subscript>5 + δ</Subscript>

(Y,M)BaCuFeO_{5 + δ} (M = Ce, Ca, Na), Y(Ba,K)CuFeO_{5 + δ}, YBa(Cu,Co)FeO_{5 + δ}, YBaCu(Fe,M)O_{5 + δ} (M = Zn, Nb), (Y,Ca)BaCu(Fe,Zn)O_{5 + δ}, and (Y,Ca)(Ba,La)Cu(Fe,Zn)O_{5 + δ} solid solutions have been prepared by ceramic processing techniques and have been characterized by x-ray diffraction, IR absorption spectroscopy, and thermal expansion and electrical conductivity (σ) measurements in air at temperatures from 300 to 1100 K. It is shown that, in the range 650–700 K, the linear thermal expansion coefficient of the (Y,M)BaCuFeO_{5 + δ} phases rises from (11–12) × 10^?6 to (14–15) × 10^?6 K^?1, while that of the YBa(Cu,Co)FeO_{5 + δ} solid solution decreases from 18 × 10^?6 to 14 × 10^?6 K^?1. The conductivity data (an increase in σ upon Ca²⁺ → Y³⁺ and Zn²⁺ → Fe³⁺ substitutions and a reduction in σ upon Ce⁴⁺ → Y³⁺ and Nb⁵⁺ → Fe³⁺ substitutions) demonstrate that the transport properties of YBaCuFeO_{5 + δ} can be tuned by electron-hole doping.     

Structural relaxation and electrical conductivity of molybdovanadate glass

⁵⁷Fe Mössbauer spectrum of conductive barium iron vanadate glass with a composition of 20BaO·10Fe₂O₃·70V₂O₅ (in mol%) showed paramagnetic doublet peak due to distorted Fe^IIIO₄ tetrahedra with isomer shift (δ) value of 0.37 (±?0.01) mm s^?1. Mössbauer spectra of 20BaO·10Fe₂O₃·xMoO₃·(70???x)V₂O₅ glasses (x?=?20–50) showed paramagnetic doublet peaks due to distorted Fe^IIIO₆ octahedra with δ’s of 0.40–0.41 (±?0.01) mm s^?1. These results evidently show a composition-dependent change of the 3D-skeleton structure from “vanadate glass” phase, composed of distorted VO₄ tetrahedra and VO₅ pyramids, to “molybdate glass” composed of distorted MoO₆ octahedra. After isothermal annealing at 500 °C for 60 min, Mössbauer spectra also showed a marked decrease in the quadrupole splitting (Δ) of Fe^III from 0.70 to 0.77 to 0.58–0.62 (±?0.02) mm s^?1, which proved “structural relaxation” of distorted VO₄ tetrahedra which were randomly connected to FeO₄, VO₅, MoO₆, FeO₆ and MoO₄ units by sharing corner oxygen atoms or edges. DC-conductivity (σ) of barium iron vanadate glass (x?=?0) measured at room temperature was 3.2?×?10^?6 S cm^?1, which increased to 3.4?×?10^?1 S cm^?1 after the annealing at 500 °C for 60 min. The σ’s of as-cast molybdovanadate glasses with x’s of 20–50 were ca. 1.1?×?10^?7 or 1.2?×?10^?7S cm^?1, which increased to 2.1?×?10^?2 (x?=?20), 6.7?×?10^?3 (x?=?35) and 1.9?×?10^?4 S cm^?1 (x?=?50) after the annealing at 500 °C for 60 min. It was concluded that the structural relaxation of distorted VO₄ tetrahedra was directly related to the marked increase in the σ, as generally observed in several vanadate glasses.     

Giant Magnetic Heat Induction of Magnesium‐Doped γ‐Fe2O3 Superparamagnetic Nanoparticles for Completely Killing Tumors

Magnetic fluid hyperthermia has been recently considered as a Renaissance of cancer treatment modality due to its remarkably low side effects and high treatment efficacy compared to conventional chemotheraphy or radiotheraphy. However, insufficient AC induction heating power at a biological safe range of AC magnetic field (H_appl·f_appl < 3.0–5.0 × 10⁹ A m^?1 s^?1), and highly required biocompatibility of superparamagnetic nanoparticle (SPNP) hyperthermia agents are still remained as critical challenges for successful clinical hyperthermia applications. Here, newly developed highly biocompatible magnesium shallow doped γ‐Fe₂O₃ (Mg_0.13‐γFe₂O₃) SPNPs with exceptionally high intrinsic loss power (ILP) in a range of 14 nH m² kg^?1, which is an ≈100 times higher than that of commercial Fe₃O₄ (Feridex, ILP = 0.15 nH m² kg^?1) at H_appl·f_appl = 1.23 × 10⁹ A m^?1 s^?1 are reported. The significantly enhanced heat induction characteristics of Mg_0.13‐γFe₂O₃ are primarily due to the dramatically enhanced out‐of‐phase magnetic susceptibility and magnetically tailored AC/DC magnetic softness resulted from the systematically controlled Mg²⁺ cations distribution and concentrations in octahedral site Fe vacancies of γ‐Fe₂O₃ instead of well‐known Fe₃O₄ SPNPs. In vitro and in vivo magnetic hyperthermia studies using Mg_0.13‐γFe₂O₃ nanofluids are conducted to estimate bioavailability and biofeasibility. Mg_0.13‐γFe₂O₃ nanofluids show promising hyperthermia effects to completely kill the tumors.     

Surface modification of Fe3O4 nanoparticles with dextran via a coupling reaction between naked Fe3O4 mechano-cation and naked dextran mechano-anion: A new mechanism of covalent bond formation

A surface modified Fe₃O₄ nanoparticle with dextran, possessing a core-shell structure, was synthesized by vibration ball-milling of Fe₃O₄ with dextran in the solid state under vacuum. A combination of experimental results and density functional theory calculations demonstrate that the surface modified Fe₃O₄ nanoparticle with dextran was performed via a coupling reaction between a “naked” Fe⁺ atom of Fe₃O₄ mechano-cation and a “naked” O^? atom of dextran mechano-anion, viz., a “Fe:O” bond-formation. The naked Fe⁺ atom of Fe₃O₄ mechano-cation was produced by ionic scission of FeO bond of Fe₃O₄ and lost an “electron pair” under the ionic scission. The naked :O^? atom of dextran mechano-anion was produced by ionic scission of CO bond comprising the α-1,6 glycosidic linkage of the dextran and gained the electron pair under the ionic scission. The Fe:O bond formation, viz., a novel type covalent bond formation, was achieved via an electron pair donation from the naked :O^? atom and its acceptance by the naked Fe⁺ atom. Consequently, a shared “electron pair” comprising the Fe:O bond was only donated from the naked :O^? atom. Our work demonstrates a novel method to form covalent bond formation between metal oxides and organic polymers, and provides a novel functionalized nanoparticle.     

Iron species in fusion-cast,glassy-phase-containing corundum materials; EPR and susceptibility analyses

By means of EPR, susceptibility, EMP, light-microscopic, thermal and chemical methods the influence of production conditions and subsequent treatments on glassy-phase-containing corundum materials were studied. Melting of the system (Al₂O₃, SiO₂, Na₂O, Fe₃O₄) under reductive conditions leads to a reduction of Fe³⁺ species contained to Fe²⁺ and even to Fe⁰ clusters with ferromagnetic behaviour. Both species markedly influence the mechanical properties of the material by increase of their volumes in consequence of oxidation in subsequent thermal processes. The following model with regard to the localization of the iron species in the system ensues: Fe(III) in corundum, Fe₂O₃, Fe₃O₄ and (scarcely) in the glassy phase; Fe(II) in the glassy phase, FeAl₂O₄ (hercynite) as a solid solution in corundum, and Fe₃O₄; (Fe⁰) clusters in corundum. It is therefore not surprising that grinding of the compact material considerably alters the magnetic properties of the samples.     

Glycothermal synthesis of fluorinated Fe3O4 microspheres with distinct peroxidase-like activity

The intrinsic peroxidase-like activity of magnetite (Fe₃O₄) has to be improved to activate H₂O₂ under mild conditions for practical applications. Herein fluorinated Fe₃O₄ microspheres (F-Fe₃O₄-r, r: 0.1–3), where r indicates the F/Fe molar ratio in the reaction mixture, were prepared by glycothermal synthesis and characterized by various complementary techniques. Fluoride ions were enriched on the surface of F-Fe₃O₄-1, and may substitute lattice oxygen or ion-exchange with surface hydroxyl groups. Kinetic study showed that the apparent activation energy for catalytic decomposition of H₂O₂ over F-Fe₃O₄-1 was significantly lower than those over unmodified Fe₃O₄ or other heterogeneous peroxidase-like catalysts (20.3 vs. 32.8–142?kJ?mol^?1), which improved the low-temperature activity of the former (decomposition rate of H₂O₂ at 25?°C: 0.0150?h^?1). Potential applications of F-Fe₃O₄-1 in wastewater treatment were demonstrated by catalytic degradation of orange G with H₂O₂ at pH 6.8 and 25?°C.     

Constructing Multifunctional Heterostructure of Fe2O3@Ni3Se4 Nanotubes

Heterostructures have attracted increasing attention due to their amazing synergetic effects, which may improve the electrochemical properties, such as good electrical/ionic conductivity, electrochemical activity, and mechanical stability. Herein, novel hierarchical Fe₂O₃@Ni₃Se₄ nanotubes are successfully fabricated by a multistep strategy. The nanotubes show length sizes of ≈250–500 nm, diameter sizes of ≈100–150 nm, and wall thicknesses of ≈10 nm. The as‐prepared Fe₂O₃@Ni₃Se₄ nanotubes with I_Ni:Fe = 1:10 show excellent Li storage properties (897 mAh g^?1 high reversible charge capacity at 0.1 A g^?1), good rate performance (440 mAh g^?1 at 5 A g^?1), and outstanding long‐term cycling performance (440 mAh g^?1 at 5 A g^?1 during the 300th cycle) as an anode material for lithium ion batteries. In addition, the Fe₂O₃@Ni₃Se₄ nanotubes with I_Ni:Fe = 1:10 (the atomic ratio between Ni and Fe) show superior electrocatalytic performance toward the oxygen evolution reaction with an overpotential of only 246 mV at 10 mA cm^?2 and a low Tafel slope of 51 mV dec^?1 in 1 m KOH solution.     

Kinetic sorption study of Cerium (IV) on magnetite nanoparticles

Magnetite nanoparticles (Fe₃O₄) and humic acid-coated magnetite nanoparticles (Fe₃O₄/HA) were prepared by co-precipitation method for cerium ions removal from aqueous solution. The success of preparation in nanoscale was confirmed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The TEM image shows that the size of Fe₃O₄ is around 15 nm and the presence of humic acid reduces the magnetite aggregation and stabilizes the magnetite suspension. Adsorption studies with respect to various process variables such as contact time, pH, and temperature were investigated by batch technique. The sorption kinetics and isotherms of Fe₃O₄ and Fe₃O₄/HA for Ce (IV) ions show that the sorption kinetics follow the pseudo-second-order and Langmuir isotherm models for both sorbents. The maximum capacities (Q_max) of Ce (IV) onto Fe₃O₄ and Fe₃O₄/HA were found to be 160 and 280 mg/g, respectively. The thermodynamic parameters (ΔG^o, ΔH^o and ΔS^o) were calculated, and the results revealed that the sorption process of Ce (IV) ions on both Fe₃O₄ and Fe₃O₄/HA are spontaneous, endothermic for Fe₃O₄ and exothermic for Fe₃O₄/HA.     

X-ray diffraction and57Fe Mössbauer spectra of the system Fe2O3−Ga2O3

The influence of gallium substitution on the chemical and structural properties of haematite, α-Fe₂O₃, has been studied using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. The presence of only α-(Ga _x Fe_1?x )₂O₃ phase is detected for the compositions withx between 0.01 and 0.90. A gradual decrease of the unit-cell parameters of α-(Ga _x Fe_1?x )₂O₃ with the increase of gallium substitution is measured.⁵⁷Fe Mössbauer spectra showed that the value of the magnetic hyperfine field of pure α-Fe₂O₃ decreases with increasing gallium for iron substitution. The hyperfine magnetic structure, which is observed for α-(Ga _x Fe_1?x )₂O₃ at room temperature, collapsed for the composition withx?0.50. The changes in the⁵⁷Fe Mössbauer spectra of the α-(Ga _x Fe_1?x )₂O₃ phase are discussed in the sense of the electronic relaxation and the superparamagnetic effects.     

Studies on the solid solutions,LnV1−xMxO3 (Ln:La,Gd or Y,M:Cr or Fe)

Electrical and magnetic properties of the solid solutions LnV_1?xM_xO₃ (Ln:La, Gd or Y, M:Cr or Fe) were studied in the temperature range 77–1000K. These solid solutions were all semiconductors. Their conductivity at room temperature decreased with Cr³⁺ or Fe³⁺ ion concentrations. The solid solutions LaV_1?xM_xO₃ and YV_1?xM_xO₃ (M:Cr or Fe) revealed an antiferromagnetism with a weak ferromagnetism and their ordering temperature increased with x. Most of the gadolinium-containing compounds were paramagnets in the measured temperature range. YV_0.4Fe_0.6O₃ showed a thermal hysteresis at high temperatures.     

Structural studies of a new electroceramic composite: Pb(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> (PFN)-Cr<Subscript>0.75</Subscript>Fe<Subscript>1.25</Subscript>O<Subscript>3</Subscript>(CRFO)

A study of the structural characteristics of the composites [Pb(Fe_0.5Nb_0.5)O₃(PFN)] _x -[Cr_0.75Fe_1.25O₃(CRFO)]_100?x (x = 0 (CRFO100), 10, 50, 90, 100) was performed in this work. The compounds PFN100 and CRFO100 were prepared by conventional solid-state method and investigated by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and ⁵⁷Fe Mössbauer Spectroscopy techniques. The X-ray analysis shows that PFN100 is tetragonal and the CRFO100 phase has a trigonal symmetry. The refinement of all the composites was also performed and discussed in this paper. The Mössbauer spectrum for the composite samples shows a paramagnetic doublet and a sextet probably assigned to a magnetic phase associated to Fe⁺³. For the sample PFN100, only a magnetic field of 49.5 T (isomer shift (δ) = 0.21 mm/s) was detected. For the composite sample, the δ and Δ are typical of Fe ions at sites of octahedral coordination.