Structural and magnetic investigations of Fe2O3–TeO2 glasses

A series of tellurite glasses containing Fe₂O₃ with the nominal composition x(Fe₂O₃)–(1−x)(TeO₂), where x = 0.05, 0.10, 0.15, and 0.20, have been synthesized and investigated using X-ray photoelectron spectroscopy (XPS) and magnetization techniques. The Te 3d core level spectra for all glass samples show symmetrical peaks at essentially the same binding energies as measured for TeO₂ indicating that the chemical environment of the Te atoms in these glasses does not vary significantly with the addition of Fe₂O₃. Furthermore, the full-width at half-maximum (FWHM) of each peak does not vary with increasing Fe₂O₃ content which suggests that the Te ions exist in a single configuration, namely TeO₄ trigonal bipyramid (tbp). The O 1s spectra are narrow and symmetric for all compositions such that oxygen atoms in the Te–O–Te, Fe–O–Fe and Te–O–Fe configurations must have similar binding energies. The analysis of the Fe 3p spectra indicates the presence of Fe³⁺ ions only, which is consistent with the valence state of the Fe ions determined from magnetic susceptibility measurements.     

Single‐crystal growth and characterization of mullite‐type orthorhombic Bi2M4O9 (M = Al3+, Ga3+, Fe3+)

Pure and homogeneous single crystals of orthorhombic mullite‐type Bi₂M₄O₉ (M = Al³⁺, Ga³⁺, Fe³⁺), and a mixed Bi₂Fe_1.7Ga_2.3O₉ crystal from an equimolar Ga/Fe composition were grown by the top seeded solution growth (TSSG) method. All these compounds melt incongruently in the range of about 800 and 1100 °C. In case of bismuth gallate and ferrate inclusion‐free crystals with dimensions up to several cubic centimeters can be grown. Limited solubility in Bi₂O₃ and the high steepness of the liquidus curve are the reasons for getting only small imperfect bismuth aluminate crystals. In contrast to ceramic materials preparation reported in literature, divalent calcium and strontium could not be incorporated into the mullite‐type structure during the melt growth process. Several fundamental physical properties like heat capacity, thermal expansion, heat conductivity, elastic constants, high‐pressure behavior and oxygen diffusivity were determined by different research groups using single‐crystalline samples from the as‐grown materials. Furthermore, the refractive indices of Bi₂Ga₄O₉ were measured in the range of 0.430 and 0.700 μm. Such as many other bismuth containing compounds the refractive indices of Bi₂Ga₄O₉ are larger than 2, and Bi₂Ga₄O₉ is an optic biaxial positive crystal. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Determination of the crystal structure of diopside (Ca0.8Fe0.2)(Mg0.8Fe0.2)Si2O6 from the Gazakh Trough (Azerbaijan)

The crystal structure of a clinopyroxene is determined by X-ray diffraction. The unit cell parameters are as follows: a = 9.732(7) ?, b = 8.896(6) ?, c = 5.280(4) ?, and ?? = 106.160(11)°; V = 439.1(5) ?³; space group C2/c; and Z = 4. The structure is determined by the direct method and refined in the anisotropic approximation by the full-matrix least-squares method (R[F ² > 2??(F ²)] = 0.027, wR(F ²) = 0.072). According to the results of the X-ray structure analysis, the crystal chemical formula of the compound is (Ca_0.8Fe_0.2)(Mg_0.8Fe_0.2)Si₂O₆. In the structure, columns of (Mg, Fe)-octahedra are connected on two sides with Si₂O₆ chains. The resulting structural units have the [(Mg,Fe)₂(Si₂O₆)₂]^4? composition. These units form a heterogeneous framework, which is typical of all pyroxene structures. The [(Mg,Fe)₂(Si₂O₆)₂]^2? composition of the framework corresponds to the ratio [(Mg,Fe) + Si]: O = 3: 6 (1: 2). The (Ca, Fe) atoms are located in the holes of the framework.     

Structural properties of Cr2O3–Fe2O3–P2O5 glasses,Part I

The structural properties of xCr₂O₃–(40 − x)Fe₂O₃–60P₂O₅, 0 ⩽ x ⩽ 10 (mol%) glasses have been investigated by Raman and Mössbauer spectroscopies, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The Raman spectra show that the addition of up to 5.3 mol% Cr₂O₃ does not produce any changes in the glass structure, which consists predominantly of pyrophosphate, Q¹, units. This is in accordance with O/P ≈ 3.5 for these glasses. The increase in glass density and T_g that occurs with increasing Cr₂O₃ suggests the strengthening of glass network. The Mössbauer spectra indicate that the Fe²⁺/Fe_tot ratio increases from 0.13 to 0.28 with increasing Cr₂O₃ content up to 5.3 mol%, which can be related to an increase in the melting temperature from 1423 to 1473 K. After annealing, the 10Cr₂O₃–30Fe₂O₃–60P₂O₅ (mol%) sample was partially crystallized and contained crystalline β-CrPO₄ and Fe₃(P₂O₇)₂. The SEM and AFM micrographs of the partially crystallized sample revealed randomly distributed crystals embedded in a homogeneous glass matrix. EDS analysis indicated that the glass matrix was rich in Fe₂O₃ (39.6 mol%) and P₂O₅ (54.9 mol%), but contained only 5.5 mol% of Cr₂O₃. These results suggest that the maximum solubility of chromium in these iron phosphate melts is 5.5 mol% Cr₂O₃.     

On the local coordination of Fe in Fe2O3-glass and Fe2O3-glass ceramic systems containing Pb, Na and Si

The effect of the composition and casting temperature on the structural role of Fe in a series of binary (Fe₂O₃-PbO and Fe₂O₃-Na₂O) and ternary (Fe₂O₃-PbO-SiO₂) glass and glass ceramic materials is studied by means of X-ray fluorescence (XRF) mapping, X-ray absorption fine structure (XAFS) and Mössbauer spectroscopies. According to the Mössbauer results the majority of Fe exists in the Fe⁺³ state. The XRF maps reveal that Fe-rich islands evolve into the vitreous matrix of ternary samples that contain more than 40 wt% Fe₂O₃. In these samples the XAFS results disclose that 40-43 at.% of the Fe atoms belong to the Fe-rich microcrystalline islands formed by Fe_xO_y oxides. Furthermore, the structural role of Fe⁺³ in the ternary glasses is found to depend on the Fe₂O₃ content. Finally in the binary Fe₂O₃-PbO systems the majority of Fe⁺³ is octahedrally coordinated in the Fe₂O₃ and/or PbFe₁₂O₁₉ crystalline phases.     

Properties of Sm‐doped CaNb2O6 thin films deposited by radio‐frequency magnetron sputtering

Sm‐doped CaNb₂O₆ (CaNb₂O₆:Sm) phosphor thin films were prepared by radio‐frequency magnetron sputtering on sapphire substrates. The thin films were grown at several growth temperatures and subsequently annealed at 800 °C in air. The crystallinity, surface morphology, optical transmittance, and photoluminescence of the thin films were investigated by X‐ray diffraction, scanning electron microscopy, ultraviolet‐visible spectrophotometry, and fluorescence spectrophotometry, respectively. All of the thin films showed a main red emission radiated by the transition from the ⁴G_5/2 excited state to the ⁶H_9/2 ground state of the Sm³⁺ ions and several weak bands under ultraviolet excitation with a 279 nm wavelength. The optimum growth temperature for depositing the high‐quality CaNb₂O₆:Sm thin films, which was determined from the luminescence intensity, was found to be 400 °C, where the thin film exhibited an orthorhombic structure with a thickness of 370 nm, an average grain size of 220 nm, a band gap energy of 3.99 eV, and an average optical transmittance of 85.9%. These results indicate that the growth temperature plays an important role in controlling the emission intensity and optical band gap energy of CaNb₂O₆:Sm thin films.     

Liquid Phase Epitaxy (LPE) of YB2Cu3O7-δ High Tc Superconductors

YBa₂Cu₃O_7-δ films were grown by liquid phase epitaxy in Y-ZrO₂ crucibles on (110)NdGaO₃ substrates. A change in the preferred crystallographic growth direction was observed reproducibly. The growth mode changes from pure c-axis oriented over mixed c/a-axis oriented films to pure a-axis oriented films with increasing undercooling. X-ray diffraction measurements and atomic force microscopy investigations with c-axis oriented as well as a-axis oriented films are presented. It will be shown that atomically smooth steps with 0.2-0.8 μM width can be achieved by LPE, which are free from melt remnants. Furthermore the values for the enthalpy of dissolution from literature, which are varying in a wide range, will be combined and a new value will be calculated in terms of a multi particle model.     

Rapid synthesis of dendrite‐ and platelet‐like α‐Fe2O3 via a hydrothermal oxidation route

Dendrite and platelet‐like α‐Fe₂O₃ microcrystals were synthesized by the oxidation reaction of K₄Fe(CN)₆and NaClO₃ through a simple hydrothermal method. The structures and morphologies of the as‐prepared samples were characterized in detail by X‐ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The experiment results show that NaOH played an important role in controlling the morphology of the final products. The possible mechanism was discussed to elucidate the formation of different morphologies of the α‐Fe₂O₃ microstructures. Besides, the magnetic property of the dendrite α‐Fe₂O₃ microstructure was characterized by a vibrating sample magnetometer (VSM). (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

X-ray Molecular and Crystal Structure Study of the Fe(II) Complex Containing 1,10-Phenanthroline and Saccharin: [Fe(C12H8N2)3] (C6H4COSO2N)2 · 4 H2O

X-ray molecular and crystal structure of the [Fe(C₁₂H₈N₂)₃] (C₆H₄COSO₂N)₂ · 4 H₂O is reported. In the complex, the Fe atom is bonded to the six nitrogen atoms with a distorted octahedral stereochemistry.     

Influence of Fe2O3 Doping on TiO2 Electrode for Enhancement Photovoltaic Efficiency of Dye-Sensitized Solar Cells

In this work, we report for the first time the improvement of the photovoltaic characteristics of dye-sensitized solar cells (DSSCs) by doping TiO₂ with Fe₂O₃. DSSCs were fabricated using various percentages of Fe₂O₃-doped TiO₂ composite nanoparticles. The Fe₂O₃-doped DSSCs exhibited a maximum conversion efficiency of 5.76% because of the effective electron transport. DSSCs based on Fe₂O₃-doped TiO₂ films showed better photovoltaic performance than cells fabricated with only TiO₂ nanoparticles. This result was attributed to the prevention of recombination between electrons in the TiO₂ conduction band with the dye or electrolytes. A mechanism was suggested based on impedance results, which indicated improved electron transport at the interface of the TiO₂/dye/electrolyte.     

Crystal structure and magnetic properties of nanosized Mg(Fe0.8Ga0.2)2O4-δ films on Si substrates

Film samples of nominal Mg(Fe_0.8Ga_0.2)₂O_4-δ composition were obtained on Si(100) substrates by oxygen-ion-beam sputtering of a Mg(Fe_0.8Ga_0.2)₂O_4-δ ceramic target. The film thicknesses were ～200 and ～400 nm. Field dependences of the specific magnetization of ～200-nm films annealed at different temperatures (800–1000°C) have been measured. The crystal structure, surface morphology, and magnetic characteristics of films of different thicknesses (～200 and ～400 nm) are investigated. The reasons for the discrepancy between the specific magnetizations of the films obtained and their ceramic analog are discussed.     

Hole defects in the crystal structure of synthetic lipscombite (Fe 4.7 3+ Fe 2.3 2+ )[PO4]4O2.7(OH)1.3 and genetic crystal chemistry of minerals of the lipscombite-barbosalite series

The crystal structure of a synthetic analog of the mineral lipscombite (Fe _2.3 ²⁺ Fe _4.7 ³⁺ )[PO₄]₄O_2.7(OH)_1.3 obtained under hydrothermal conditions in the LiF-Fe₂O₃-(NH₄)₂HPO₄-H₂O system is resolved (R = 0.040) by X-ray diffraction analysis (Bruker Smart diffractometer with a highly sensitive CCD detector, MoK _α radiation): a = 14.776(3) Å, b = 14.959(3) Å, c = 7.394(1) Å, β = 119.188(4)°, sp. gr. C2/c, Z = 4, ρ_exp = 3.8 g/cm³, ρ_calcd = 3.9 g/cm³. Fe²⁺ and Fe³⁺ cations are statistically distributed in each of four crystallographically independent positions, while occupying the corresponding octahedra with probabilities of 60, 90, 100, and 91%. The ratio Fe²⁺/Fe³⁺ in the composition of the crystals was established by Mössbauer spectroscopy. Lipscombite is interpreted as a mineral of variable composition described by the formula (Fe _x ²⁺ Fe _n?x ³⁺ )[PO₄]₄O_y(OH)_4?y . The field of stability is determined as a function of the iron content and the ratio Fe²⁺/Fe³⁺. It is shown that at n = 6 iron cations are ordered in octahedra and barbosalite structure is formed. An interpretation of genetically and structurally related members of the lipscombite family within a unified polysomatic series is proposed.     

Optical absorption spectra of LiNbO3, Fe:LiNbO3, and Zn:Fe:LiNbO3 single crystals grown by Bridgman method

The optical absorption spectra of LiNbO₃ (LN), Fe:LiNbO₃ (Fe:LN), and Zn:Fe:LiNbO₃ (Zn:Fe:LN) single crystals grown by Bridgman method were measured and compared. The absorption characteristics of the samples and the effects of growth process conditions on the absorption spectra were investigated. The Fe, Zn and Li concentrations in the crystals were analyzed by inductively coupled plasma (ICP) spectrometry. The results indicated that the overall Fe ion and Fe²⁺ concentration in Fe:LN and Zn:Fe:LN crystals increased along the growing direction. The incorporation of ZnO in Fe:LN crystal induced increase of Fe²⁺ in the crystal. Among Fe‐doped and Zn:Fe‐codoped LN single crystals, 3 mol% ZnO doped Fe:LN had a biggest change of Fe²⁺ ion concentration from bottom to top part of crystal. The effects of technical conditions (atmosphere and thermal history) on Fe²⁺ ion concentration were discussed. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An investigation of the local iron environment in iron phosphate glasses having different Fe(II) concentrations

The local environment around iron ions in iron phosphate glasses of starting batch composition 40Fe₂O₃-60P₂O₅ (mol%) melted at varying temperatures or under different melting atmospheres has been investigated using Fe-57 Mössbauer and X-ray absorption fine structure (XAFS) spectroscopies. Mössbauer spectra indicate that all of the glasses contain both Fe(II) and Fe(III) ions. The quadrupole splitting distribution fits of Mössbauer spectra show that Fe(II) ions occupy a single site whereas Fe(III) ions occupy two distinct sites in these glasses. When melted at higher temperatures or in reducing atmospheres, the Fe(II) fraction in the glass increases at the expense of Fe(III) ions at only one of the two sites they occupy. The pre-edge feature in the XAFS data suggests that the overall disorder in the near-neighbor environment of iron ions decreases with increasing Fe(II) fraction. The XAFS results also show that the average iron-oxygen coordination is in the 4-5 range indicating that iron ions have mixed tetrahedral-octahedral coordination.     

MOCVD growth of GaN on Si(1 1 1) substrates using an ALD-grown Al2O3 interlayer

GaN thin films have been grown on Si(1 1 1) substrates using an atomic layer deposition (ALD)-grown Al₂O₃ interlayer. This thin Al₂O₃ layer reduces strain in the subsequent GaN layer, leading to lower defect densities and improved material quality compared to GaN thin films grown by the same process on bare Si. XRD ω-scans showed a full width at half maximum (FWHM) of 549 arcsec for GaN grown on bare Si and a FWHM as low as 378 arcsec for GaN grown on Si using the ALD-grown Al₂O₃ interlayer. Raman spectroscopy was used to study the strain in these films in more detail, with the shift of the E₂(high) mode showing a clear dependence of strain on Al₂O₃ interlayer thickness. This dependence of strain on Al₂O₃ thickness was also observed via the redshift of the near bandedge emission in room temperature photoluminescence (RT-PL) spectroscopy. The reduction in strain results in a significant reduction in both crack density and screw dislocation density compared to similar films grown on bare Si. Screw dislocation density of the films grown on Al₂O₃/Si substrates approaches that of typical GaN layers on sapphire. This work shows great promise for the use of oxide interlayers for growth of GaN-based LEDs on Si.     

Purity and doping possibilities of Al2O3 and YAG molten in Mo crucibles and crystals grown from this melt

Doping possibilities of Al₂O₃ and YAG crystals grown from the melt alternatively doped with alkali earth, silicon, iron group or molybdenum ions under 98% Ar – 2% H₂ or 98% He – 2% H₂ protective atmosphere are described. Alkali earth and particularly Si ions evaporate slowly from the melt. Reduction of iron group ions was observed. Mo may enter YAG phase using a wet protective atmosphere. Al₂O₃ phase contains Mo ions if grown from the electrolyzed melt.     

A Mössbauer Study of the Interaction between Fe2O3 and TeO2

The interaction between Fe₂O₃ and TeO₂ by vacuum sintering at various temperature was studied The compounds obtained were identified by means of Mössbauer spectroscopy. The conditions for the synthesis of Fe₂ Te₄O₁₁ were found. Some influence of the experimental conditions was established.     

Fabrication of Fe3O4 octahedra by a triethanolamine‐assisted hydrothermal process

Octahedral Fe₃O₄microcrystals were synthesized using a triethanolamine‐assisted route under hydrothermal conditions. The chemical compositions and morphologies of the as‐prepared samples were characterized in detail by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). During the hydrothermal process for the preparation of Fe₃O₄ octahedra, the possible mechanism was discussed to elucidate the formation of the octahedral Fe₃O₄microcrystals. Triethanolamine and hydrazine hydrate play important roles in the formation of the final products. The magnetic property of sample was evaluated on a vibrating sample magnetometer (VSM) at room temperature. The values of saturation magnetization and coercivity of octahedral Fe₃O₄are about 103 emu/g and 157 Oe, respectively. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nuclear57Fe relaxation in Fe2+-containing NiFe2O4 and CoFe2O4 single crystals

Spin-lattice (T ₁) and spin-spin (T ₂) relaxation times of ⁵⁷Fe nuclei in the single-crystal NiFe₂O₄ and CoFe₂O₄ ferrites containing Fe²⁺ ions have been studied in the temperature range of 4.2–100 K by a spin-echo technique. The peaks of relaxation rates T ₁ ^?1 and T ₂ ^?1 caused by the presence of Fe²⁺ ions were observed for both ferrites in the ranges 38–42 and 28–32 K, respectively. The analysis of the results obtained with invocation of the data on ferromagnetic resonance and the measurements of the temperature dependence of resistivity shows that the mechanism of nuclear relaxation responsible for “impurity” peaks and is a slow relaxation process caused by electron exchange Fe²⁺ ? Fe³⁺, characterized by a low activation energy.     

Crystal Growth,Thermal and Linear Optical Properties of the Non‐Centrosymmetric Hydrated Tetraborates Na2[B4O5(OH)4] . 3H2O (Tincalconite) and K2[B4O5(OH)4] . 2H2O

Large single crystals of the non‐centrosymmetric hydrated tetraborates Na₂[B₄O₅(OH)₄] . 3H₂O (Tincalconite) (point group 32) and K₂[B₄O₅(OH)₄] . 2H₂O(point group 222) were grown from aqueous solutions and the linear optical properties (refractive indices between 365 nm and 1530 nm and unpolarized absorption spectra) as a basis for nonlinear optical investigations were determined. The uniaxial positive sodium salt is not phase matchable; in the orthorhombic potassium compound type I phase matching is possible in the near infrared region. Thermal investigations indicate a phase transition at ≈285 K for Na₂[B₄O₅(OH)₄] . 3H₂O.