X-ray K-absorption studies ofsome ruthenium compounds

X-ray K-absorption studies of ruthenium in ruthenium metal,RuO₂, K₂(RuCl₆) and K₄[Ru(CN)₆]: 3H₂O have been carried out using 400 mm bent crystal (mica) spectrograph. K-absorption edge of ruthenium in these compounds lies on the higher energy side with respect to that in the ruthenium metal; the divalent K₄[Ru(CN)₆]·3H₂O gives the shift in the range of tetravalent compounds RuO₂ and K₂[RuCl₆]. This discrepancy has been explained on the basis of molecular orbital picture.     

X-ray spectroscopic investigation of some spinel structures

K-absorption edges of cations in the manganites of magnesium, nickel, copper, zinc and cadmium and ferrite samples of composition, Mg_1?x Mn_x Fe₂O₄ (x=0, 0·25, 0·50, 0·75, 1·0), have been recorded employing a 40 cm curved mica crystal spectrograph of transmission type. It is observed that the absorption edges for the specimen shift towards the shorter wavelength side of the metal edge position. Shifts of both the absorption edges and the main absorptoin peaks for ferrites and manganites have been compared with compounds in which the oxidation state of the cation is well known. It is found that the manganese ions in these ferrites and manganites exist in valence states two and three respectively while iron in the ferrite samples is present in oxidation state three. An attempt has been made to interpret the observed absorption edge features in the light of neutron and X-ray diffraction studies on the same ferrite and manganite samples.     

Analysis of XPS spectra of Fe and Fe ions in oxide materials

Samples of the iron oxides Fe_0.94O, Fe₃O₄, Fe₂O₃, and Fe₂SiO₄ were prepared by high temperature equilibration in controlled gas atmospheres. The samples were fractured in vacuum and high resolution XPS spectra of the fractured surfaces were measured. The peak positions and peak shape parameters of Fe 3p for Fe²⁺ and Fe³⁺ were derived from the Fe 3p XPS spectra of the standard samples of 2FeO·SiO₂ and Fe₂O₃, respectively. Using these parameters, the Fe 3p peaks of Fe₃O₄ and Fe_1−yO are analysed. The results indicate that high resolution XPS techniques can be used to determine the Fe²⁺/Fe³⁺ ratios in metal oxides. The technique has the potential for application to other transition metal oxide systems.     

Chemical shifts in strontium compounds by X-ray spectroscopy

The positions of the X-ray K-absorption edge of strontium in various compounds and in aqueous solutions have been measured. With the help of modified Moseley diagram the wavelength of the X-ray K-absorption edge of Strontium in metal has been extrapolated. Chemical shifts of the K-absorption edge with respect to this extrapolated value have been presented. The fine structure has been observed on the high energy side of the main absorption edge both in Rubidium and Strontium compounds. Bond lengths for various compounds have been calculated from the maxima-minima separations. The chemical shifts of fluorescence Kα_1,2 lines with respect to their position in Sr²⁺ ion have also been studied. While the edge shift with respect to the edge in free ion is towards the low energy side, the line shift with respect to the line in free ion is towards the high energy side.     

X-ray K-absorption studies of molybdenum sulphide,selenides and tellurides

X-ray K-absorption studies of molybdenum sulphide, selenides and tellurides have been carried out using 400-mm bent crystal (mica) spectrograph. K-absorption edge of molybdenum in its selenides, tellurides and sulphide lies on the higher energy side with respect to that in the molybdenum metal; the shift in higher selenide and telluride, namely MoSe₂ and MoTe₂ being smaller than that in the lower selenide and telluride, Mo₃Se₄ and Mo₃Te₄ respectively. On the other hand selenium K-absorption edge changes from low energy side in Mo₃Se₄ to higher energy side in MoSe₂ with respect to that in the selenium metal.     

Magnetic and structural properties of CaO–SiO2–P2O5–Na2O–Fe2O3 glass ceramics

Magnetic properties of glass ceramics derived from glasses with composition 41CaO·(52−x)SiO₂·4P₂O₅·xFe₂O₃·3Na₂O (2?x?10 mol% iron oxide (Fe₂O₃)) are reported. Structural investigation revealed the presence of nanocrystalline magnetite phase in the heat-treated samples containing x?2 mol% Fe₂O₃. Magnetic hysteresis cycles of the glass-ceramic samples were obtained with a maximum applied field of ±20 kOe as well as a low field of ±500 Oe, in order to evaluate the potential of these glass ceramics for hyperthermia treatment of cancer. Samples with x>2 mol% of iron oxide exhibited magnetic behavior similar to soft magnetic materials with low coercivity. The evolution of magnetic properties in these samples as a function of iron oxide molar concentration is correlated with the amount and crystallite size of magnetite phase present in them.     

X-ray spectroscopic study of cobalt-zinc ferrites

K-absorption edges and the associated fine structures of cobalt and iron in cobalt-zinc ferrites of composition, Zn_xCo_1-xFe₂O₄ (x = 0, 0.25, 0.50 and 0.75) have been recorded employing a 40cm curved crystal spectrograph of transmission type. It is found that the cobalt and iron ions in these samples exist in valence states two and three respectively. Bond lengths have been determined using the X-ray fine structure methods. It is noted that estimated bond lengths are close to those obtained from crystallographic data. It is pointed out that the X-ray fine structure methods can be used to complement diffraction methods for the determination of bond lengths in samples containing atoms of nearly equal scattering power.     

Surface oxidation study of Fe67Co18B14Si1 metallic glass using Auger electron spectroscopy

Surface composition and depth profile of native oxide on Fe₆₇Co₁₈B₁₄Si₁ metallic glass has been investigated using Auger electron spectroscopy. The native oxide is compared with chemisorbed oxygen on the cleaned surface. Results indicate that boron segregates on the surface in the presence of oxygen. The low energy L₂₃M₄₅M₄₅ peak of iron in metallic glass is compared with that in crystallized sample and pure iron foil.     

Characterization of iron(III) oxide films used for photoelectrode by means of cems

Thin iron oxides deposited on semi-conductive glass by a spray pyrolysis technique were analysed by Conversion Electron Mössbauer Spectrometry (CEMS). Iron oxide deposited on SnO₂ coated glass was composed of a large grained particles of crystalline α?Fe₂O₃, which showed sextet. The doublet and sextet appeared in CEM spectra of iron oxides deposited on In₂O₃ and WO₃ coated glasses. The sextet was due to α?Fe₂O₃ and the doublet was attributted to the superparamagnetic microcrystalline α?Fe₂O₃ (≈15nm) rather than to spinel compounds of iron. The iron oxide deposited on ZnO coated glass gave a doublet in CEM spectra. It was supporsed to be due to very fine particle of α?Fe₂O₃ (<100nm). It was found that iron oxide films obtained by spray pyrolysis were dependent on the kinds and the temperature of the semi-conductive materials coated on glass.     

Resonant soft X-ray scattering studies of multiferroic YMn2O5

We performed soft X-ray resonant scattering at the MnL _2,3- and OK edges of YMn₂O₅. While the resonant intensity at the Mn L _2,3 edges reflects the magnetic order parameter, the resonant scattering at the O K edge is found to be directly related to the macroscopic ferroelectric polarization. The latter observation reveals the important role of the spin-dependent Mn-O hybridization for the multiferroicity of YMn₂O₅. We present details about how to obtain correct energy dependent lineshapes and discuss the origin of the resonant intensity at the O K edge.     

X-ray emission study of the electronic structure of nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Valence states of metal ions and the phase composition of nanocrystalline Al₂O₃ (of the original oxide and the oxide irradiated by high-energy Fe⁺ ions) are studied by using x-ray emission Al L_{2, 3} and O Kα spectra. It is established that the shape of the Al L_{2, 3} spectra strongly changes as one goes from the original (bulk) Al₂O₃ to nanocrystalline oxide, while the O Kα spectra remain practically unchanged. Moreover, irradiation by high-energy Fe⁺ ions results in slight additional changes in the x-ray spectral characteristics of the aluminum oxides under study. The obtained experimental data are compared with the results of theoretical calculations of the electronic structure of α and γ phases of Al₂O₃ performed using the LDA formalism. Using the results of x-ray spectral studies, electronic structure calculations, and x-ray diffraction analysis, it is shown that the revealed spectral differences between the nanocrystalline state of aluminum oxide and the bulk material can be interpreted as a phase transition from the α phase to the γ phase of Al₂O₃ with an addition of bayerite.     

Study of Cu K-edge in some copper (II) square planar complexes

The copper K-absorption edge in the complexes Cu(ammonia)₂ C₂O₄, Cu(methylamine)₂ C₂O₄, Cu(ethylamine)₂ C₂O₄ and Cu(aniline)₂ C₂O₄ has been investigated using the Cauchois-type bent crystal X-ray spectrograph. Three peaks, A, B and C, observed in the edges have been explained on the basis of molecular orbital theory.     

Intrinsic ultraviolet luminescence of LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> single crystals under inner-shell excitation

Ultraviolet photoluminescence (PL) of LiB₃O₅ (LBO) crystals has been studied under selective excitation by photons in the vacuum ultraviolet and ultrasoft x-ray regions, including the K-absorption edges of the Li and B cations and O anion. Radiative recombination of electron-hole pairs was established to be the main channel of the intrinsic PL excitation at 4.2 eV. Features were observed in the PL excitation spectra near the lithium and boron K-absorption edges originating from excitation of the cation 1s core excitons. Experimental evidence of the multiplication of Li 1s excitons in LBO was obtained. It is shown that excitation of the O 1s core excitons does not affect the PL yield noticeably. The differences in the appearance of the Li, B, and O 1s excitons in the excitation spectra of the LBO ultraviolet PL are discussed.     

Changes in the state of iron atoms in Zr alloys during corrosion tests in an autoclave

Mössbauerinvestigations were carried out on oxide films formed on specimens of zirconium alloys Zr-1.0 %wtFe-1.2 %wtSn-0.5 %wtCr subjected to corrosion in steam-water environment at a temperature of 360 °C and at a pressure of 16.8 MPa with lithium and boron additions, and on Zr-1.4 %wtFe-0.7 %wtCr corroded in steam-water environment at 350 °C and 16.8 MPa as well as in steam-water environment at 500 °C and 10 MPa. In the metal part of the samples, under the oxide film, the iron atoms are in form of intermetallic precipitates of Zr(Fe, Cr)₂. The corrosion process decomposes the intermetallic precipitates and particles are formed of metallic iron with inclusions of chromium atoms –Fe(Cr), α–Fe₂O₃ and Fe₃O₄ compounds. Part of the iron ions are in divalent and part in trivalent paramagnetic states. It is proposed that some part of the iron containing oxide precipitates in the oxide film may be in the form of nanoparticles which pass from the superparamagnetic to the ferromagnetic state with decreasing temperature.     

X-ray absorption spectral investigations on mixed-valence copper complexes of penicillamine and cysteamine

The X-ray K-absorption spectra of copper in some of its complexes involving ligands like penicillamine (known detoxicating agent for heavy metal poisoning) and cysteamine (a known radiation protector) have been investigated using a 40 cm curved crystal spectograph. These complexes are described in the literature as being mixed-valence [1, 2]. The copper-penicillamine complex shows two distinct edges, K₁ and K₂, indicating mixed-valency in the complex. The cysteamine complexes do not show any splitting of the edges. In one of the cysteamine complexes, which is said to involve molecular oxygen, the magnitudes of shifts of the main edge and principal absorption maximum fall close to copper (II) compounds whereas in the other complex, these shifts are in the range of copper (I) compounds. The probable reasons for the observed deviations have been discussed.     

Structural and optical properties of porous iron oxide

The structural and optical properties of the novel porous iron oxide fabricated by wood template have been investigated. The obtained porous iron oxide was characterized to be α- Fe₂O₃ by Fourier transform infrared and Raman spectroscopy. X-ray absorption fine structure measurement revealed that the bond length of Fe-O₁ of the porous iron oxide has good agreement with that reported for the α- Fe₂O₃ crystal structure while the bond lengths for Fe-O₂ and Fe-Fe deviate slightly from those of the α- Fe₂O₃ crystal structure. Photoluminescence from the porous iron oxide exhibited broad emission bands around 760 and 890 nm, which are believed to be due to the unique nanoscale structure of the porous iron oxide.     

Mössbauer and ESR investigation of the behaviour of iron in vanadium borophosphate glasses

Mössbauer and ESR measurements were performed on vanadium borophosphate glasses containing iron. The glass composition was 78 mole% V₂O₅, 15 mole% P₂O₅, 7 mole% B₂O₃ and different amounts of Fe₂O₃ (0.5–50 mole%) were added. The relative percentage of iron in different states and site positions could be determined for each glass composition. Correlation between the behaviour of iron and its variation in structural units and other physical properties are proposed. A maximum amount of 33 mole% Fe₂O₃ could be incorporated in the glass network, higher concentrations lead to the precipitation of α-Fe₂O₃.     

Yolk–Shell‐Structured Cu/Fe@γ‐Fe2O3 Nanoparticles Loaded Graphitic Porous Carbon for the Oxygen Reduction Reaction

Core–shell Cu/γ‐Fe₂O₃@C and yolk–shell‐structured Cu/Fe@γ‐Fe₂O₃@C particles are prepared by a facile synthesis method using copper oxide as template particles, resorcinol‐formaldehyde as the carbon precursor, and iron nitrate solution as the iron source via pyrolysis. With increasing carbonization temperature and time, solid γ‐Fe₂O₃ cores are formed and then transformed into Fe@γ‐Fe₂O₃ yolk–shell‐structured particles via Ostwald ripening under nitrogen gas flow. The composition variations are studied, and the formation mechanism is proposed for the generation of the hollow and yolk–shell‐structured metal and metal oxides. Moreover, highly graphitic carbons can be obtained by etching the metal and metal oxide nanoparticles through an acid treatment. The electrocatalytic activity for oxygen reduction reaction is investigated on Cu/γ‐Fe₂O₃@C, Cu/Fe@γ‐Fe₂O₃@C, and graphitic carbons, indicating comparable or even superior performance to other Fe‐based nanocatalysts.     

Mossbauer, infrared and magnetic susceptibility studies of iron sodium borate glasses doped by sulphur

The affect of sulphur on the structural properties of iron sodium diborate glasses having the composition {(100−x)Na₂B₄O₇+xFe₂O₃}+yS, where x=0.05, 0.15 and 0.25 mol% and Y=0, 2.5 and 5 wt% was studied by infrared, Mossbauer spectroscopy and magnetic susceptibility measurements. It was found that, for samples having 5 mol% Fe₂O₃ and free from sulphur, the iron ions are present in both Fe²⁺ and Fe³⁺ states and also 92% of the total iron enters the glass network as a glass former. The ratio of Fe³⁺/Fe²⁺ increases with increasing the iron content for sulphur-free samples and others containing sulphur. This ratio also decreases with increasing the sulphur content. The magnetic susceptibility was found to decrease with increasing the sulphur content. Also, the increase of Fe₂O₃ content led to a less symmetrical environment of Fe³⁺ ions and vice versa for the Fe²⁺ environment.     

Deep reduction behavior of iron oxide and its effect on direct CO oxidation

Reduction of metal oxide oxygen carrier has been attractive for direct CO oxidation and CO₂ separation. To investigate the reduction behaviors of iron oxide prepared by supporting Fe₂O₃ on γ-Al₂O₃ and its effect on CO oxidation, fluidized-bed combustion experiments, thermogravimetric analyzer (TGA) experiments, and density functional theory (DFT) calculations were carried out. Gas yield (γCO₂) increases significantly with the increase of temperature from 693 K to 1203 K, while carbon deposition decreases with the increase of temperature from 743 K to 1203 K, where temperature is a very important factor for CO oxidation by iron oxide. Further, it were quantitatively detected that the interaction between CO and Fe₂O₃, breakage of O-Fe bonds and formation of new C-O bonds, and effect of reduction degree were quantitatively detected. Based on adsorptions under different temperatures and reducing processes from Fe³⁺ into Fe²⁺, Fe⁺ and then into Fe, it was found that Fe²⁺ → Fe⁺ was the reaction-controlling step and the high oxidation state of iron is active for CO oxidation, where efficient partial reduction of Fe₂O₃ into FeO rather than complete reduction into iron may be more energy-saving for CO oxidation.