Crystal growth,X-ray diffraction characterization,and Mössbauer spectroscopy of FeIn<Subscript>2</Subscript>S<Subscript>4</Subscript>-In<Subscript>2</Subscript>S<Subscript>3</Subscript> solid solutions

Crystals of (FeIn₂S₄)_{1 ? x} (In₂S₃) _x solid solutions consisting of large blocks have been grown by directional solidification (horizontal Bridgman process). FeIn₂S₄, In₂S₃, and the solid solutions are shown to crystallize in the spinel structure. The composition dependence of their unit-cell parameter a follows Vegard's law. The local states of the Fe ions in the solid solutions have been studied by Mössbauer spectroscopy in a transmission geometry.     

Effect of sintering temperature on the dielectric and varistor properties of SnO<Subscript>2</Subscript>–Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript> composite ceramics

The effect of sintering temperature from 1350 to 1450 °C on the dielectric and varistor properties of SnO₂–Zn₂SnO₄ composite ceramics has been systematically investigated. With the increasing of sintering temperature, the average grain size increased from about 1 to 5 μm and the breakdown electric field decreased from 117 to 3 V/mm. The relative dielectric constant increased with sintering temperature and it achieved the maximum of 1.2 × 10⁴ (40 Hz, 0 °C) at 1425 °C. With excessive increasing of sintering temperature, the relative dielectric constant decreased and the microstructure of the ceramic bulk became porous. In the spectra of imaginary part of the complex modulus, a peak was exhibited and the peak’s position shifted to high frequency with increasing testing or sintering temperature. The activation energy related to the peak was about 0.4 eV and this value was thought to be associated with the oxygen vacancies. Based on the sintering effect, the mechanism of oxygen vacancies in SnO₂–Zn₂SnO₄ composite ceramics was proposed and accordingly, the varistor and giant permittivity properties are well understood based on the grain boundary barrier model.     

Mössbauer spectroscopy and X-ray diffraction of oxide precipitates formed from FeSO4 solution

Chemical and structural properties of oxide precipitates formed from FeSO₄ solution were investigated using X-ray diffraction and⁵⁷Fe Mössbauer spectroscopy. The hydrolysis of urea at elevated temperature was used for the generation of OH^– ions during the precipitation process. The formation of particular oxide phase in the precipitate is strongly dependent on the concentrations of FeSO₄ and urea, as well as on the rate of oxygenation. The phase analysis of precipitates showed the presence of different oxide phases, such as goethite, lepidocrocite, hematite and magnetite, and in one sample of a small amount of siderite. Only substoichiometric magnetite, Fe_3–x O₄, was detected. Significant differences in the Mössbauer spectrum of goethite were observed, due to a very small particle size, the degree of crystallinity and/or different content of structurally bonded water. The correlation between the Mössbauer spectra of precipitated goethite and goethite formed during the atmospheric corrosion of steel is discussed.     

Prolonged lifetime and enhanced separation of photogenerated charges of nanosized α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> by coupling SnO<Subscript>2</Subscript> for efficient visible-light photocatalysis to convert CO<Subscript>2</Subscript> and degrade acetaldehyde

To develop efficient visible-light photocatalysis on α-Fe2O3,it is highly desirable to promote visible-light-excited high-energy-level electron transfer to a proper energy platform thermodynamically.Herein,based on the transient-state surface photovoltage responses and the atmosphere-controlled steady-state surface photovoltage spectra,it is demonstrated that the lifetime and separation of photogenerated charges of nanosized α-Fe2O3 are increased after coupling a proper amount of nanocrystalline SnO2.This naturally leads to greatly improved photocatalytic activities for CO2 reduction and acetaldehyde degradation.It is suggested that the enhanced charge separation results from the electron transfer from α-Fe2O3 to SnO2,which acts as a proper energy platform.Based on the photocurrent action spectra,it is confirmed that the coupled SnO2 exhibits longer visible-light threshold wavelength (～590 nm) compared with the coupled TiO2 (～550 nm),indicating that the energy platform introduced by SnO2 would accept more photogenerated electrons from α-Fe2O3.Moreover,electrochemical reduction experiments proved that the coupled SnO2 possesses better catalytic ability for reducing CO2 and O2.These are well responsible for the much efficient photocatalysis on SnO2-coupled α-Fe2O3.     

Mössbauer Analysis and Cation Distribution of Zn Substituted BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> Hexaferrites

Barium hexaferrite is a well-known hard magnetic material. Doping using nonmagnetic cation such as Zn²⁺ were found to enhance magnetization owing to preferential tetrahedral site (4 f ₁) occupancy of the zinc. However, the distribution of cations in hexaferrites depends on many factors such as the method of preparation, nature of the cation, and chemical composition. Here, Zn-doped barium hexaferrites (Ba_1?xZn_xFe₁₂O₁₉) were synthesized by sol-gel method. In this study, we summarized the magnetic properties of Ba_1?xZn_xFe₁₂O₁₉ (x = 0, 0.1, 0.2, 0.3) BaM, investigated by Mössbauer spectroscopy. Moreover, cation distribution was also calculated for all the products. Mössbauer parameters were determined from 57Fe Mössbauer spectroscopy and according to it, the replacement of Ba-Zn affects all parameters such as isomer shift, the variation in line width, hyperfine magnetic field, and quadrupole splitting. Cation distribution revealed the relative area of undoped BaM, 12k, 2a, and 4 f ₂ positions which are close to theoretical values.     

Small angles X-ray diffraction and Mössbauer characterization of annealed Tb/Fe multilayer

The effect of thermal annealing on the structure and magnetic properties of crystalline Tb/Fe multilayers has been studied using conversion electron M?ssbauer spectrometry and small-angle X-ray diffraction. The growth of Tb–Fe amorphous alloy from the interface is observed with increasing annealing temperature. After annealing at 873 K, a clear total mixing of the multilayers by interdiffusion has been evidenced. The results are compared with the effect of ion irradiation in the same system.     

Crystallographic and magnetic properties of Fe-doped SnO<Subscript>2</Subscript> nanopowders obtained by a sol–gel method

We prepared Sn_1?x Fe _x O₂ (x = 0, 0.03, 0.05, 0.10, and 1.0) nanoparticles by the polymeric precursor method based on the modified Pechini process. Two types of starting reactants for both tin and iron were explored: Sn(II)/Fe(II) and Sn(IV)/Fe(III) precursors. Thermogravimetric analysis revealed that the precursor powders prepared from Sn(IV) have higher excess in ethylene glycol in comparison to precursor samples prepared from Sn(II). XRD patterns for those samples prepared from Sn(IV) and Fe(III) were adequately fitted by introducing only the cassiterite phase of SnO₂. Micro-Raman spectra also support these findings, and additionally it is found that the presence of iron broadened and reduced the intensities of the principal bands. ¹¹⁹Sn Mössbauer spectra indicated only the presence of Sn⁴⁺, whereas RT ⁵⁷Fe Mössbauer spectra suggested the presence of two Fe³⁺ sites located at different distorted sites. On the other hand, micro-Raman and ⁵⁷Mössbauer spectrometry showed the formation of hematite as impurity phase for those samples with iron concentrations above ~5 at.%, prepared from Fe(II) and Sn(II) precursors. In addition, their XRD patterns revealed larger average grain sizes for the cassiterite phase of SnO₂ in comparison to those samples prepared from Sn(IV) and Fe(III).     

High- and low-temperature X-ray diffraction studies of aluminate spinels in the CoAl<Subscript>2</Subscript>O<Subscript>4</Subscript>–NiAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

Co _x Ni_1–x Al₂O₄ (x = 0, 0.25, 0.5, 0.75, 1) aluminate spinels have been prepared by solid-state reactions and their crystal structures have been refined by the Rietveld method. We have analyzed whether the results are consistent with theoretical relationships stemming from the hard sphere model. Using high- and low-temperature X-ray diffraction measurements, we have obtained the temperature dependences of the unit-cell parameters for the synthesized compounds and determined their thermal expansion coefficients. The rate of cation exchange reactions has been shown to be very slow at temperatures below 200°C.     

Probe Mössbauer Spectroscopy of BiNi<Subscript>0.96</Subscript><Superscript>57</Superscript>Fe<Subscript>0.04</Subscript>O<Subscript>3</Subscript>

This paper presents results of a ⁵⁷Fe probe Mössbauer spectroscopy study of the BiNi_0.96⁵⁷Fe_0.04O₃ nickelate. The spectra measured above its TN demonstrate that Fe³⁺ cations heterovalently substitute for Ni²⁺ nickel (←Fe³⁺), being stabilized on four sites of the nickel sublattice in the structure of BiNiO₃. Calculations in an ionic model with allowance for monopole and dipole contributions to the electric field gradient indicate that the parameters of electric hyperfine interactions between ⁵⁷Fe probe atom nuclei reflect the specifics of the local environment of the nickel in the structure of the unsubstituted BiNiO₃ nickelate. Below T^N, Mössbauer spectra transform into a complex Zeeman structure, which is analyzed in terms of first-order perturbation theory with allowance for electric quadrupole interactions as a small perturbation of the Zeeman levels of the ⁵⁷Fe hyperfine structure, as well as for specific features of the magnetic ordering of the Ni²⁺ cations in the nickelate studied.     

Local crystal structure of multiferroic BiMnO<Subscript>3</Subscript> studied by <Superscript>57</Superscript>Fe probe Mössbauer spectroscopy

This paper presents a ⁵⁷Fe probe Mössbauer spectroscopy study of a BiMn_0.96⁵⁷Fe_0.04O₃ manganite synthesized at high pressure (6 GPa). The BiMnO₃ manganite possesses multiferroic properties and exhibits cooperative orbital ordering due to Jahn–Teller active Mn³⁺ ions. ⁵⁷Fe Mössbauer spectra have been measured and analyzed in a wide temperature range, which includes the orbital ordering temperature of BiMnO₃.     

Synthesis and characterization of TiO<Subscript>2</Subscript>–NiO and TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> nanocomposites

TiO₂–NiO and TiO₂–WO₃ nanocomposites were prepared by hydrothermal and surface modification methods. The samples were analyzed using X-ray diffraction, Scanning Electron Microscope images, Transmission Electron Microscope, Energy dispersive analysis, Zeta potential, Electrophoretic mobility and Photocatalysis activity measurement. XRD data sets of TiO₂–NiO, TiO₂–WO₃ powder nanocomposite have been studied for the inclusion of NiO, WO₃ on the anatase-rutile mixture phase of TiO₂ by Rietveld refinement. The cell parameters, phase fraction, the average grain size, strain and bond lengths between atoms of individual phases have been reported in the present work. Shifted positional co-ordinates of individual atoms in each phase have also been observed.     

Synthesis of supported SnO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> catalysts for the deep oxidation of methane

A new method has been proposed for the synthesis of catalytically active 80 wt % SnO₂ + 20 wt % CeO₂ materials supported on glass fiber, which involves the use of an ethanolic film-forming solution based on cerium(III) nitrate and salicylic acid, with the addition of tin(IV) chloride. We have studied the morphology of the materials thus prepared and assessed their catalytic activity for the deep oxidation of methane. The results indicate that the appreciable catalytic activity of the materials is ensured by their uniform distribution over the support surface and the small oxide aggregate size ( 10 μm), which is due to the use of the filmforming solution of the proposed composition.     

X-ray diffraction characterization and electrical properties of TlIn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>2</Subscript> crystals

Single crystals of TlIn_{1 − x} Ga _x Te₂ solid solutions have been grown and characterized by X-ray diffraction, and their electrical conductivity, Hall coefficient, and thermoelectric power have been measured as functions of temperature. Partial substitution of gallium for indium in TlInTe₂ increases its unit-cell parameters.     

Microstructure development and nonlinear electrical characteristics of the SnO<Subscript>2</Subscript>·CuO·Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> based varistors

The microstructure development of SnO₂·CuO based ceramic material was analyzed by XRD and SEM and the electrical properties were investigated by J-E relation. The secondary phases of copper oxide were found by the XRD. Copper oxide could make tin oxide densify and advance the grain growth, while tantalum oxide would retard the grain growth. Excess copper would centralize at the grain boundaries and prevent the mass transport. The high nonlinear coefficient (α = 27.3) and low leakage current density (J_L = 16 μA cm⁻²) for the 0.05 mol% Ta₂O₅-doped SnO₂·CuO based varistor sample were obtained. The modified defect barrier model for CuO and Ta₂O₅-doped SnO₂ based varistors was introduced.     

Synthesis and characterization of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> nanocomposite powder by sucrose process

Nanocrystalline alumina–zirconia powders were prepared by a modified chemical route using sucrose, polyvinyl alcohol (PVA) and metal nitrates followed by a post calcination process. The process involved dehydration of Al³⁺–Zr⁴⁺ ions-sucrose–PVA solution to a highly viscous liquid which on decomposition process produced a black precursor material. The obtained precursor were then calcined at various temperatures: 1,050, 1,100, 1,150, 1,200 and 1,250 °C for different soaking times (1, 2, 4 h) in air. The formation of a nanocomposite composed of α-alumina (~20 nm) and tetragonal (t) zirconia (~19 nm) crystallites were confirmed for the sample calcined at 1,200 °C for 2 h, based on our XRD and TEM results. However, for the samples calcined below 1,150 °C the composite formed were composed of metastable alumina (γ, δ, θ) as well as t-zirconia phases. Interestingly, the zirconia phase retained its tetragonal structure for all the samples calcined above 1,050 °C. This is possibly related to the “size effect” and reduction of surface enthalpy of the zirconia crystallites surrounded by Al³⁺ cations.     

Sequence of phase transformations and inhomogeneous magnetic state in nanosized Sr<Subscript>2</Subscript>FeMoO<Subscript>6 – δ</Subscript>

We have studied the effect of synthesis conditions on the phase composition, grain size and morphology, degree of superstructural ordering, and magnetic properties of the Sr₂FeMoO_6–δ double perovskite. The results demonstrate that its magnetic state, dependent on the nonuniformity of grain morphology and the degree of superstructural ordering of the iron and molybdenum cations, correlates with the initial solution pH. Analysis of the sequence of phase transformations during strontium ferromolybdate crystallization in the citrate gel process from a pH 4 starting solution allowed us to propose combined conditions that ensure the preparation of single-phase Sr₂FeMoO_6–δ powder with an average grain size in the range 50–120 nm and the highest degree of superstructural ordering of the iron and molybdenum cations: P = 88%.     

Magnetic and Mössbauer Studies of Ba(Fe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>As<Subscript>2</Subscript> Single Crystals

Magnetization and ⁵⁷Fe Mössbauer effect spectroscopy (MS) studies of Ba(Fe_1?x Ni _x )₂As₂ single crystals (x=0 to 0.054) at temperatures (5 K to 300 K) have been performed. Magnetic measurements show that for BaFe₂As₂ the magnetic moment decreases below T _N=136 K. T _N is suppressed monotonically by Ni doping. On the other hand, for higher x values the magnetic moment increases below T _N. Unexpectedly for x=0.024 (T _N=67 K), the virgin zero-field-cooled (ZFC) curve is higher than that of field-cooled (FC) one below 48 K. The magnetic MS spectra of this sample are composed of a superposition of two subspectra, corresponding to commensurate and incommensurate field distributions. The average magnetic hyperfine field H _eff decreases with T and becomes zero at 80 K. For higher x values, the samples become superconducting at T _C=15.5 and 19 K for x=0.046 and 0.054, respectively. For both samples below T _C, the FC curves are positive (the paramagnetic Meissner effect) up to applied field of H～15 Oe and the susceptibility is inversely proportional to H. The MS spectra below and above T _C are almost identical, indicating that the MS parameters are not sensitive enough to detect the superconducting state. The peculiar phenomena observed are attributed to disorder induced by the presence of Ni atoms in the Fe sublattice.     

Synthesis and properties of actinide dimolybdate complexes M<Subscript>2</Subscript>[AnO<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>2</Subscript>]·H<Subscript>2</Subscript>O (M = Rb,Cs; An = Np,Pu)

New Np(VI) and Pu(VI) dimolybdates Rb₂NpO₂(MoO₄)₂·H₂O (I), Cs₂NpO₂(MoO₄)₂·H₂O (II), Cs₂PuO₂(MoO₄)₂·H₂O (III), and Rb₂PuO₂(MoO₄)₂·H₂O (IV) were synthesized under hydrothermal conditions. The crystal structures of the compounds were determined, and their absorption spectra in the UV, visible, and IR ranges were measured. The compounds crystallize in the monoclinic system. Their crystal structure is based on [AnO₂(MoO₄)₂]_n^2n– anionic layers (An = Np, Pu) formed by (AnO₂)O₅ pentagonal bipyramids and MoO₄ tetrahedra, sharing common vertices. Each An atom in the layer is bonded to other five An atoms via MoO₄ tetrahedra with the formation of a 4343² network. The effect of the ionic radius of the outer-sphere cation on the parameters of the crystal structure and features of the absorption spectra is discussed.