Effect of iron oxide (Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) on the structural,optical, electrical,and dielectric properties of SrO–V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The oxide glass system of the composition (10 – x)SrO–xFe₂O₃–90V₂O₅, (x = 0, 2, 4, 6 and 8 mol %) were prepared by a standard melt quenching technique. The amorphous nature of the prepared glass was confirmed using X-ray diffraction technique. The infrared spectra of these glasses were recorded over a continuous spectral range (850–1500 cm^–1). The density of prepared sample was obtained by the Archimedes principle. The physical parameters of the glasses were also determined with respect to the composition. Density increases from 3.10 to 3.20 g/cm³, whereas the molar volume decreases with the increase in Fe₂O₃ concentration. In order to study optical properties, absorption spectra were measured at room temperature. Indirect optical energy band gap, optical dielectric constant, refractive index were calculated from optical energy band gap. The refractive index decreases gradually with the increase in Fe₂O₃ content due to increase of bridging oxygen’s. For temperatures from 300 to 500 K, the dc conductivity increased with the increasing Fe₂O₃ content. The dielectric properties like dielectric constant, dielectric loss factor and dielectric loss tangent investigated at the room temperature in the frequency range of 10 kHz to 1 MHz decreases with frequency. The dielectric behavior shows strong frequency as well as composition dependence.     

EPR and optical studies on binary mixed alkali-alkaline earth oxide borate glasses doped with Cu<Superscript>2+</Superscript> ions

Mixed alkali alkaline earth oxide borate glasses of the composition (25 – x)Li₂O–xK₂O–12.5BaO–12.5MgO–49B₂O₃–1CuO (x = 0, 5, 10, 15 and 20 mol %) were prepared by the melt quenching technique. The X-ray diffractograms of all the glass samples were recorded at room temperature. Peak free X-ray spectra revealed the amorphous nature of all the prepared glasses. Modulated differential scanning calorimetry (MDSC) was used to determine the glass-transition temperature (T _g ). The probable mixed alkali effect was investigated using experimental techniques like density, molar volume, MDSC, electron paramagnetic resonance (EPR), and optical absorption studies. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values indicated that the ground state of \(C{u^{2 + }}is{\kern 1pt} {d_{{x^2} - {y^2}}}\) orbital (²B_1g) and the site symmetry around Cu² is tetragonally distorted octahedral. The variation of g _|| and A _|| as a function of Li₂O content was found to be nonlinear. A broad optical absorption band was observed in all the glasses containing Cu² ions corresponding to ²B_1g → ²B_2g transition. From the optical absorption studies the values of the optical band gap (E _opt) for indirect, direct transitions and Urbarch energy (ΔE) have been evaluated. By co-relating the EPR and optical absorption data, bonding parameters α², β² and β ₁ ² were evaluated.     

Parameters of luminescence and the local structure of Eu<Superscript>3+</Superscript> centers in fluorogermanate glasses

The influence of the chemical nature of the local environment of Eu³⁺ ions on the parameters of luminescence of these centers in glasses of the (BaGeO₃)_{1 ? x ? y} (Al₂O₃) _x (0.45CaF₂ · 0.55MgF₂) _y (x = 0.25, y = 0; x = 0.17, y = 0.17; x = 0.15, y = 0.22; x = 0.07, y = 37.00; x = 0, y = 0.45) system is investigated. The oxidation state of europium atoms and the degree of homogeneity of their local environment in the glasses are determined using ¹⁵¹Eu Mössbauer spectroscopy.     

Photon interaction parameters for some ZnO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Some photon interaction parameters such as mass attenuation coefficient, effective atomic number, half value layer, mean free path and electron density for 15ZnO–(17.5–x)Al₂O₃–xFe₂O₃–67.5P₂O₅ glass system (x = 0, 7.5, 12.5, 17.5) and 15ZnO–(25–x)Al₂O₃–xFe₂O₃–60P₂O₅ glass system (x = 0, 25) have been investigated in the photon energy range of 1 keV to 100 GeV. It has been observed that all the photon interaction parameters for the selected glass systems vary with the photon energy. Among the selected glass systems, the sample 15ZnO–25Fe₂O₃–60P₂O₅ glass system shows maximum values for mass attenuation coefficients, effective atomic numbers, electron densities and minimum values for mean free path and half value layer in the entire energy grid.     

AC Conductivity and Dielectric Behavior of Silicophosphate Glass Doped by Nd<Subscript>2</Subscript>O<Subscript>3</Subscript>

Silicophosphate glasses of nominal composition (P₂ O ₅ 50%-SiO₂ 30%-Na₂O 20%) and Nd₂ O ₃ additive (0.5 and 2 wt%) were prepared and dielectric behavior has been studied over a temperature range (302–483 K) in the frequency range (0.5 - 3243 kHz). Frequency dependence of AC conductivity (σ _ac), has been explored using the universal power law. Disparity of the frequency exponent (s) with temperature was examined in terms of diverse conduction mechanisms. The principal conduction mechanisms were found correlated to both barrier hopping (CBH) and quantum mechanical tunneling (QMT) models. Temperature dependence of σ _ac (ω) showed a linear increase with different frequencies. In addition, the capacitance, loss tangent, dielectric loss and dielectric constant were calculated over variable temperature ranges and frequencies.     

Structure-Property Relations in Barium Borate Glasses from Raman Scattering Data

Glasses in the xBaO-(100 ? x)B₂O₃ system (x = 16–50 mol %) are investigated by Raman spectroscopy. The spectral forms of stoichiometric groupings are separated from the experimental Raman spectra. The diagram of the content of these groupings in glasses is constructed. The diagram obtained makes it possible to calculate the densities, refractive indices, temperature coefficients of linear expansion, and fractions of four-fold-coordinated boron atoms with the use of the experimentally determined partial properties of the groupings. It is revealed that the dependences of the boson peak intensity, the boson peak frequency, and the glass transition temperature on the composition of glasses in the barium borate system correlate with each other.     

Study of polaron transport mechanisms in two transition metal ions doped borophosphate glasses

Borophosphate glasses in the compositions, (B₂O₃)_0.2 · (P₂O₅)_0.3 · (V₂O₅) _x · (CoO)_0.5x , where x = 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50 were synthesized at 1500 K by standard melt quenching method. Non-crystalline nature of the samples was confirmed by XRD studies. Room temperature density and dc electrical conductivity in the temperature range from 350 K to 625 K have been measured. Density decreased up to about 0.25 mole fractions of V₂O₅ and increased thereafter. Conductivity was almost constant up to 0.25 mole fractions of V₂O₅ and increased for higher amount of V₂O₅. Temperature variation of conductivity data has been analyzed using Mott’s small polaron hopping (SPH) model and, activation energy and Debye’s temperature were determined. Activation energy decreased with increase of V₂O₅ content. The data deviated from the Mott’s SPH model has been analyzed in view of variable range hopping models of Mott and Greaves and the density of states at Fermi level was determined. It is for the first time that borophosphate glasses doped with V₂O₅ and CoO were synthesized to study conductivity variation with temperature. The data analyzed using small polaron hopping and variable range hopping models.     

Synthesis of Titanates with a Ramsdellite-Type Tunnel Structure Crystallizing in the Li<Subscript>2</Subscript>O-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiO<Subscript>2</Subscript> System in Different Gaseous Media

The ramsdellite-type phases crystallizing in the Li₂O-Fe₂O₃-TiO₂ system in the course of synthesis in gaseous media at different oxygen partial pressures are studied. Solid solutions based on the ramsdellite structure with the composition Li₂Ti_3?xFe _x O_{7 ? δ} (0 ≤ x ≤ 0.7) are prepared in an oxidizing medium (P_O2 = 1 atm) for the first time. Analysis of the results obtained by electron paramagnetic resonance and Mossbauer spectroscopy revealed that, in these solid solutions, all iron ions are in the oxidation state Fe⁺³.     

Study of the Structure of Iron-Containing Zinc Borate Glass

The results of the experimental study of glass of the xFe₂O₃–(100–x)[40ZnO. 60B₂O₃] composition in which the content of iron oxide varies from 0 to 10 mol % are presented. The regularities of the glass structure change in the short- and intermediate-range order structures are considered based on the data of infrared spectroscopy and Raman spectroscopy. The valence and coordination state of iron in a glass matrix is studied by Mössbauer spectroscopy.     

Thermal expansion and polymorphism in a series of rubidium cesium boroleucites

The crystal structure of the boroleucite solid solution Rb_0.40Cs_0.54B_0.94Si_2.06O₆ is refined in space group I-43d by the Rietveld method with the use of the X-ray powder diffraction data. The refinement data complement the available crystal chemical characteristics of Rb_1?x Cs _x BSi₂O₆ solid solutions. The thermal expansion and phase transformations of Rb_1?x Cs _x BSi₂O₆ borosilicates are investigated in parallel by high-temperature X-ray diffraction with conventional powdered samples and by the dilatometric method with samples in the form of pressed pellets. It is demonstrated that the thermal expansion coefficients, as well as the temperatures and sequence of polymorphic transitions, which are determined from the data obtained by two methods are in close agreement. The temperature curve of the I-43d ? Ia3d phase transition for the Rb_1?x Cs _x BSi₂O₆ solid solution system is constructed from the data obtained by both methods. It is shown with the use of the structural data obtained by the Rietveld method that, at temperatures above 800°C, rubidium-cesium boroleucites undergo decomposition due to the release of alkali cations.     

Thermal expansion and phase transitions in K<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Rb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>BSi<Subscript>2</Subscript>O<Subscript>6</Subscript> leucite borosilicate solid solutions

Continuous solid solutions and the reversible phase transition from the I-43d cubic phase to the Ia-3d cubic phase are revealed in the borosilicate series K_{1 ? x} Rb _x BSi₂O₆. Samples in the KBSi₂O₆-RbBSi₂O₆ system are prepared by solid-phase synthesis and crystallization of glasses and investigated using the annealing and quenching technique, high-temperature X-ray diffraction, and dilatometry. The above polymorphic phase transition is observed in all solid solutions at temperatures in the range from 330 to 430°C depending on the composition: an increase in the rubidium content in the solid solution leads to a gradual decrease in the phase transition temperature. The linear thermal expansion coefficients α are determined for solid solutions of different crystalline modifications and glasses. The linear thermal expansion coefficients α for the I-43d low-temperature phase are equal to (20–23) × 10^?6 K^?1 according to the X-ray diffraction data and (21–24) × 10^?6 K^?1 according to the dilatometric data. The values of α for the Ia-3d high-temperature phase lie in the range (4–9) × 10^?6 K^?1 according to the X-ray diffraction data and in the range (6–9) × 10^?6 K^?1 according to the dilatometric data. The linear thermal expansion coefficients for both modifications decrease with an increase in the rubidium content in the solid solutions. The linear thermal expansion coefficients for glasses α = (10–11) × 10^?6 K^?1 are close to those for the high-temperature modification and virtually independent of the sample composition. The I-43d (cubic) ai I4₁/a (tetragonal) o Ia-3d (cubic) polymorphic phase transitions in the KBSi₂O₆ compound are revealed by differential scanning calorimetry (DSC) and dilatometry. Their reversibility is confirmed by the DSC data.     

Fe-doped LaCoO<Subscript>3</Subscript> perovskite catalyst for NO oxidation in the post-treatment of marine diesel engine’s exhaust emissions

New post-treatment process for marine diesel engine exhaust emissions was proposed by combining NO oxidation and wet scrubbing technology for the simultaneous removal of SO_X, NO_X and PM. NO, insoluble in aqueous scrubbing absorbent, is preferentially oxidized to NO₂, which then turns fully soluble in it. Fe substituted LaCo_1-xFe_xO₃ perovskite catalysts were developed for NO oxidation to NO₂. The catalysts were prepared by co-precipitation method and analyzed with XRD, XRF, BET, FT-IR, NO-TPD and XPS techniques. Crystal structure change from rhombohedral to orthorhombic was observed with the increased amount of Fe substituted in the B site of the perovskite by XRD analysis. From FT-IR and NO-TPD analysis, nitrate on perovskite species was found to be the active species for NO oxidation. Quantitative analysis was performed within the prepared catalysts. Catalytic activity was measured using a packed bed reactor operated at 150–400 °C, atmospheric pressure and with gas hourly space velocity (GHSV) of 20,000 h^-1 using a simulated exhaust gas composed of NO 400 ppm, O₂ 10% balanced with N2. Formation of Fe⁴⁺ cation enhanced the redox property as well as the mobility of the lattice oxygen present in the perovskite catalysts, confirmed by XPS analysis. Reaction mechanism of NO oxidation on Fe substituted LaCo_1-xFe_xO₃ was discussed based on Mars-van Krevelen mechanism.     

Magneto Optical Properties of FeB<Subscript>x</Subscript>Fe<Subscript>2−x</Subscript>O<Subscript>4</Subscript> Nanoparticles

In this study, FeB_xFe_2?xO₄ nanoparticles (NPs) were synthesized by the polyol method. The M–H hysteresis curves exhibit superparamagnetic characteristics that are both coercivity and remanent magnetization values are negligible. The particle size dependent Langevin function was applied to calculate the magnetic particle dimensions around 9 nm. The measured magnetic moments of NPs are in range of (1.52–2.2) µ_B and almost half or less with respect to 4 µ_B of bulk Fe ferrite. Magnetic anisotropy was specified as uniaxial and calculated effective anisotropy constants (K _eff ) are between 43.3 × 10⁴ and 19.4 × 10⁴ emu/g. The UV–Vis diffuse reflectance spectroscopy and Kubelka–Munk theory were used to determine the optical properties. The estimated optical band gap values (2.15–2.48 eV) of FeB_xFe_2?xO₄ NPs are bigger with respect to reported values (1.88–2.12 eV) for Fe₃O₄ NPs in the literature. The bigger E _g values are mainly attributed to B concentration and partly to quantum confinement effect.     

FTIR spectra and elastic properties of Cd-substituted Ni–Zn ferrites

Solid solutions Ni_0.5–x Cd _x Zn_0.5Fe₂O₄ (x = 0, 0.15, 0.30) were prepared by solid-state synthesis and characterized by FTIR spectroscopy. The FTIR spectra of synthesized ferrites showed two absorption bands (ν₁ and ν₂) in the range 400–600 cm^–1 belonging to tetrahedral (A) and octahedral (B) interstitial sites in the spinel lattice. The force constants for tetrahedral (K _t) and octahedral sites (K _o) were determined, as well as Young’s modulus (E), rigidity modulus (G), bulk modulus (B), Debye temperature (Θ_D), and velocity of transverse (V _t) and longitudinal (V _l) elastic waves. The relevant interionic cation–anion, cation–cation distances and bond angles are also reported.     

Synthesis and Physicochemical Properties of Nanopowders and Ceramics in a CeO<Subscript>2</Subscript>–Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> System

Nanopowders with a composition of (СeO₂)_1–x(Gd₂O₃)_x (x = 0.03, 0.05, 0.07, and 0.10) are synthesized by the coprecipitation method using cryotechnologies. The coherent scattering region (CSR) of the powders is 10–14 nm and the specific surface area is 70–81 m²/g. Based on the powders, ceramic nanosized materials with CRS of 64–71 nm are obtained. The dependence of the phase composition, microstructure, and electrical transport properties of the obtained samples on the Gd₂O₃ content is established. In a CeO₂–Gd₂O₃ system, a solid solution with the composition of (CeO₂)_0.90(Gd₂O₃)_0.10 has the highest ionic conductivity with the transfer number of ions of t_i = 0.74 at a temperature of 700°C. It is shown that ceramics of this composition can be used as a solid electrolyte of intermediate-temperature fuel cells due to their physicochemical characteristics.     

Monte Carlo Design and Experiments on the Neutron Shielding Performances of B<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Glass System

Neutron shielding properties of (90 – x)B₂O₃–10ZnO–xBi₂O₃ glass systems (where x = 15, 20, 25 and 30 mol %) were investigated by Monte Carlo simulations (FLUKA and GEANT4) and experiments. Neutron mass removal cross sections, number of inelastic scattering, elastic scattering, and capture interactions were estimated by simulations. ²⁴¹Am/Be neutron source was used for the neutron equivalent dose rate measurements. As a result, produced glass samples have fine neutron shielding capacity.     

Physical and Mechanical Properties of Neodymium Doped Zinc Borate Glass with Different Boron Content

A zinc borate glass system of composition xNa₂O-(58-x)B₂O₃-40ZnO-2Nd₂O₃(where x = 0, 5, 10, 15, 20 and 25) has been prepared using the melt quenching method. The effect of Na₂O on the crystal structure, density, molar volume and mechanical properties was investigated. X-ray diffraction analysis confirmed the amorphous nature of the prepared glass. The density and molar volume followed the normal behavior of a glass system. Ultrasonic non-destructive testing was employed for measuring the mechanical properties of the zinc borate glass system. The values of Young’s modulus and the Poisson ratio decreased with increasing the Na ⁺ concentration. Meanwhile, the microhardness, Debye temperature and acoustic impedance were diminished with increasing the Na ⁺ ion content. The results showed that the ultrasonic non destructive test measured the mechanical properties of the glass with similar accuracy to the Vickers microhardness. Such tested properties can be applied for silicate and non-silicate glasses.     

Properties of perovskite-like phases <Emphasis Type="Italic">Ln</Emphasis>BaCuFeO<Subscript>5 + δ</Subscript> (<Emphasis Type="Italic">Ln</Emphasis> = La,Pr)

The influence of the oxygen content on the crystal chemical parameters of the LnBaCuFeO_{5 + δ} (Ln = La, Pr) ferrocuprates is investigated using X-ray powder diffraction and IR spectroscopy. The electrical conductivity of these phases is studied. The chemical expansion coefficients α_δ and the activation energies E _a for electrical conduction are calculated. It is demonstrated that, for the LnBaCuFeO_{5 + δ} (Ln = La, Pr) phases, the chemical expansion coefficients ad depend on both the ionic radius of Ln ³⁺ cations and the oxygen nonstoichiometry of the ferrocuprate, whereas the activation energies E _a for electrical conduction are predominantly determined by the oxygen content in the samples.     

Alkali-thermal gasification and hydrogen generation potential of biomass

Generating hydrogen gas from biomass is one approach to lowering dependencies on fossil fuels for energy and chemical feedstock, as well as reducing greenhouse gas emissions. Using both equilibrium simulations and batch experiments with NaOH as a model alkaline, this study established the technical feasibility of converting various biomasses (e.g., glucose, cellulose, xylan and lignin) into H₂-rich gas via catalyst-free, alkalithermal gasification at moderate temperatures (as low as 300 °C). This process could produce more H₂ with less carbon-containing gases in the product than other comparable methods. It was shown that alkali-thermal gasification follows C _x H _y O _z + 2xNaOH + (x–z)H₂O = (2x + y/2–z)H₂ + xNa₂CO₃, with carbonate being the solid product which is different from the one suggested in the literature. Moreover, the concept of hydrogen generation potential (H₂-GP)—the maximum amount of H₂ that a biomass can yield, was introduced. For a given biomass C _x H _y O _z , the H₂-GP would be (2x + y/2–z) moles of H₂. It was demonstrated experimentally that the H2-GP was achievable by adjusting the amounts of H₂O and NaOH, temperature and pressure.

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SHS of pyrochlore-type ceramic matrices for immobilization of actinide-containing nuclear wastes

Mineral-like Y₂(Ti_1–x Zr _x )₂O₇ ceramic matrices for immobilization of actinide–Zr–RE-containing high-level nuclear wastes (HLW) were prepared by SHS method. In experiments, HLW were modeled by a mixture of CeO₂, La₂O₃, ZrO₂, MnO₂, and Fe₂O₃ powders. An increase in the HLW content of green mixture decreased the amount of Y₂(Ti_1–x Zr _x )₂O₇ in combustion product and increased that of ZrO₂, LaTiO₃, and CaTiO₃; decreased the fractional substitutionality of Zr for Ti; and increased the product porosity. An increase in combustion temperature and suppression of heat sink during SHS reaction did not diminish markedly the porosity of synthesized ceramics.