Spectral-luminescent investigations of glasses and glass-ceramic materials in Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-GeO<Subscript>2</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Glasses of 2Bi₂O₃-3GeO₂-xFe₂O₃ composition, where x = 0–1.5, are obtained under oxidizing and reducing conditions. Glass-ceramic materials are produced by the thermal treatment of the glasses, the properties of which, as well as those of the original glasses, are studied by the methods of X-ray phase analysis and optical and luminescent spectroscopy. It is found that the Fe³⁺/Fe²⁺ ion ratio in the samples changes depending on the synthesis conditions of the original glasses and crystallization process.     

Effect of sintering conditions on the properties of sol-gel-derived Li<Subscript>1.3</Subscript>Al<Subscript>0.3</Subscript>Ti<Subscript>1.7</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Solid electrolyte Li_1.3Al_0.3Ti_1.7(PO₄)₃ was prepared by sol-gel method under different sintering conditions. The structural identification, surface morphology, electrochemical window, ionic conductivity, and activation energy of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets were investigated by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. It is found that the sintering temperature and time have considerable effect on the properties of the Li_1.3Al_0.3Ti_1.7(PO₄)₃ sintered pellets. The Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellet sintered at 900 °C for 2 h is denser than the pellets sintered at other conditions. Different sintering conditions result in the sintered pellet with different porosity. However, the sintering conditions have little effect on the electrochemical window of Li_1.3Al_0.3Ti_1.7(PO₄)₃. Among the Li_1.3Al_0.3Ti_1.7(PO₄)₃ pellets sintered at various conditions, the pellet sintered at 900 °C for 2 h shows the highest ionic conductivity of 3.46 × 10⁻⁴ S cm⁻¹ and the lowest activation energy of 0.2821 eV.     

Kinetics of electron tunneling transfer in KH<Subscript>2</Subscript>PO<Subscript>4</Subscript> and NH<Subscript>4</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> crystals with hydrogen bonds

A model of electron transfer by tunneling between trapped electron and hole centers in crystals with hydrogen bonds under the conditions of thermostimulated mobility of one carrier type in the recombination process has been developed. The proposed model describes all features in the kinetics of induced optical density relaxation observed in nonlinear optical crystals of KH₂PO₄ (KDP) and NH₄H₂PO₄ (ADP) on a wide temporal scale (10⁻⁸–10 s) under pulsed irradiation. The results of model calculations have been compared with experimental data on the photoinduced transient optical absorption (TOA) in KDP and ADP crystals in the visible and UV ranges. The nature of the radiation-induced defects, which account for the TOA, and the dependence of the TOA decay kinetics on the temperature, excitation power, and other experimental conditions have been considered.     

Photoinduced processes in thin films of MoO<Subscript>3</Subscript> and mixed V<Subscript>2</Subscript>O<Subscript>5</Subscript>: MoO<Subscript>3</Subscript> oxides

Photoinduced processes in thin films of MoO₃ and mixed V₂O₅: MoO₃ oxides prepared by polycondensation of the respective oxoacids under solvothermal conditions are studied using Raman spectroscopy, ESR, and AFM. It is shown that, under UV irradiation, the photoinduced polycondensation occurs in the oxide films, leading to the formation of the oxygen bridges, an effect that opens up the possibility of developing a new photolithographic process.     

Properties of ferromagnetic resonance in Fe<Subscript>73.5</Subscript>CuNb<Subscript>3</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript> nanocrystalline alloys

The structural properties and parameters of ferromagnetic resonance have been studied for Fe_73.5CuNb₃Si_13.5B₉ nanocrystalline alloys produced from the initial amorphous state via annealing under different conditions. The dependence of the linewidth of the ferromagnetic resonance on the grain size ΔH ∼ D ⁶ has been found. The result is discussed within the framework of the random magnetic anisotropy model.     

Magnetic properties and the magnetoimpedance effect of nanostructured Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> ribbons with induced magnetic anisotropy

The structure and magnetic properties and the magnetoimpedance effect of nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy ribbons, obtained from the amorphous state by annealing under different conditions, were comparatively analyzed. Despite the similarity of the samples’ structural states and the processes of their quasi-static magnetization reversal, the features of the magnetoimpedance effect are indicative of significant differences in the processes of their dynamic magnetization.     

High-temperature conductivity and structure of Y<Subscript>2</Subscript>(WO<Subscript>4</Subscript>)<Subscript>3</Subscript> ceramics

The magnitude and character of conductivity were studied for Y₂(WO₄)₃ ceramics synthesized by the ceramic (from oxides) and organic-nitrate procedures. Investigation of the dependence \(\sigma \left( {{\alpha _{{o_2}}}} \right)\) and measurements of the ion transport numbers of charge carriers by the EMF method showed that Y₂(WO₄)₃ is basically an ion conductor. The conductivity is largely determined by the sample preparation conditions related to the dependence of the specific surface area and powder grain size on the synthetic procedure. The maximum high-temperature conductivity of Y₂(WO₄)₃ was 2.51 × 10^–4 S/cm, which roughly corresponds to the conductivities of Sc₂(WO₄)₃ and In₂(WO₄)₃ measured under the same conditions. It was confirmed that Y₂(WO₄)₃ crystallizes as a mixed monoclinic-orthorhombic structure at 1000°C. The character of water incorporation in hydrated Y₂(WO₄)₃ crystals was studied by thermogravimetry and diffuse reflectance IR spectroscopy. A qualitative model of water intercalation was suggested.     

Thermal properties and ionic conductivity of Li<Subscript>1,3</Subscript>Ti<Subscript>1,7</Subscript>Al<Subscript>0,3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> solid electrolytes sintered by field-assisted sintering

Li_1,3Ti_0,7Al_0,3(PO₄)₃ (LATP) powder was obtained by a conventional melt-quenching method and consolidated by field-assisted sintering technology (FAST) at different temperatures. Using this technique, the samples could be sintered to relative densities in the range of 93 to 99 % depending on the sintering conditions. Ionic and thermal conductivity were measured and the results are discussed under consideration of XRD and SEM analyses. Thermal conductivity values of 2 W/mK and ionic conductivities of 4?×?10^?4 Scm^?1 at room temperature were obtained using relatively large particles and a sintering temperature of 1000 °C at an applied uniaxial pressure of 50 MPa.     

Kinetics of the transient optical absorption in Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> and LiB<Subscript>3</Subscript>O<Subscript>5</Subscript> lithium borate crystals

This paper reports on a study of the kinetics of electron tunneling transport between electron and hole centers in Li₂B₄O₇ and LiB₃O₅ lithium borate crystals under the conditions where the mobility of one of the partners in the recombination process is thermally stimulated. A mathematical model has been proposed to describe all specific features in the relaxation kinetics of the induced optical density observed in Li₂B₄O₇ (LTB) and LiB₃O₅ (LBO) nonlinear optical crystals within a broad time interval of 10⁻⁸−1 s after a radiation pulse. The results of calculations have been compared with experimental data on transient optical absorption (TOA) of LTB and LBO crystals in the visible and ultraviolet spectral regions. The nature of the radiation defects responsible for TOA and the dependence of the TOA decay kinetics on temperature, excitation power, and other experimental conditions have been discussed.     

Evolution of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> crystals in Al-Mg-SiO<Subscript>2</Subscript> composites

The present study analyzes the morphological transformations of reaction products i.e., MgO, MgAl₂O₄ occurring during the reaction between SiO₂ and Al-Mg alloy in Al-Mg-SiO₂ composite processed by the liquid metallurgy technique. Different phases of platelet and hexagonal morphologies are detected and their composition analysis by EDS has confirmed them as being transition phases existing between MgO, MgAl₂O₄ and Al₂O₃. This study has also revealed the gradual transformation of (i) MgO needles to octahedral MgAl₂O₄ through Mg-Al-Si-O and Mg-Al-O transition phases having platelet morphologies and (ii) MgAl₂O₄ to Al₂O₃ through hexagonal transition phases on holding of Al-5Mg-SiO₂ and Al-1Mg-SiO₂ composites respectively at 1023K. Fully developed α-Al₂O₃ crystals are not observed under the present experimental conditions, wherein the Mg content is well above the equilibrium Mg content required for the formation of stable Al₂O₃ (<0.05 wt. %). PACS 05.70.Np     

Giant positive magnetoresistance in heterostructure (La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>) coated with YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7</Subscript> composites

(La_0.7Sr_0.3MnO₃) _x /(YBa₂Cu₃O₇) _y composites were prepared by mixing La_0.7Sr_0.3MnO₃ powders and the sol–gel-derived YBa₂Cu₃O₇ matrix, followed by high-temperature calcinations. Their structural, magnetic properties and magnetoresistance effect have been investigated systematically. A giant positive magnetoresistance (PMR) at low magnetic field is observed at low temperatures. In the case of (La_0.7Sr_0.3MnO₃)₁/(YBa₂Cu₃O₇)₉ composite, the PMR achieves 260% under a magnetic field of 5800 Oe. However, the PMR value sharply decreases with increasing temperature and no magnetoresistance effects are found above metal-insulator transition temperature. The enhancement of spin-dependent scattering at the grain boundaries should be responsible for the observed PMR. In addition, the temperature dependence of resistance under magnetic field could be explained by the competition between diamagnetism and paramagnetism in YBCO phase. At low temperature, the diamagnetism is predominant over paramagnetism and the interface scattering between LSMO grains is enhanced correspondingly. As a result, the low-temperature resistance increases and large PMR appears.     

Electrochemical properties of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> prepared with tartaric acid chelating agent

Lithium manganese oxide (LiMn₂O₄) has been prepared using sol-gel technique under acidic (pH = 5.8) and alkaline (pH = 9) conditions with tartaric acid as chelating agent. X-ray studies show that under acidic condition, an Mn₂O₃ peak was observed indicating the presence of impurities. No impurity was observed for LiMn₂O₄ under alkaline conditions. The particle size is mostly in the range of 124 to 185 nm from HR-TEM. The lithium diffusion coefficient, D _Li+ in LiMn₂O₄ is of the order 10^?9 cm² s^?1. By using density functional theory (DFT) calculations, structural properties have been obtained. The specific discharge capacity of the cells with LiMn₂O₄ prepared under alkaline condition and with LiMn₂O₄ prepared under acidic condition discharged at 0.5 C is in the ranges of 132 to 142 and 128 to 139 mAh g^?1, respectively.     

Structural relaxation of Zr<Subscript>41</Subscript>Ti<Subscript>14</Subscript>Cu<Subscript>12.5</Subscript>Ni<Subscript>10</Subscript>Be<Subscript>22.5</Subscript> bulk metallic glass under high pressure

Zr₄₁Ti₁₄Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) is annealed at 573 K under 3 GPa and its structural relaxation is investigated by X-ray diffraction, ultrasonic study, compression as well as sliding wear measurements. It is found that after the ZrTiCuNiBe BMG sample was annealed under high pressure, the mechanical properties were improved. Moreover, theBMG with relaxed structure exhibits markedly different acoustic properties. These results are attributed to the fact that relaxation under high-pressure results in a microstructural transformation in the BMG.     

Heterophase states in 0.10PbTiO<Subscript>3</Subscript>-0.90Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> crystals

A new model of the elastic matching of phases is proposed, and heterophase structures near the morphotropic phase boundary in 0.10PbTiO₃-0.90Pb(Zn_1/3Nb_2/3)O₃ crystals are studied. Unique behavior of the unit cell parameters is found to favor the elastic matching of the ferroelectric tetragonal and orthorhombic phases under the conditions of complete or partial relaxation of internal mechanical stresses at a volume concentration ratio of these phases of about 20/80% and temperatures of T=20–300 K. Interrelations between the volume concentrations of different domain (twin) types and of the coexisting phases are analyzed.     

Vibrational spectra of disordered oxyfluoride (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>WO<Subscript>3</Subscript>F<Subscript>3</Subscript>

Comparative analysis of the IR absorption and Raman scattering spectra of a polycrystalline sample of perovskite-type oxyfluoride (NH₄)₃WO₃F₃ has been performed in the frequency range 370–4000 cm^?1 at temperatures from 92 to 303 K, including the transition between the orientationally disordered cubic and low-symmetry phases. The conformation of WO₃F₃ octahedral groups is established and transitional anomalies of the internal modes of these groups and ammonium ions are revealed. Comparative analysis of the IR and Raman spectra suggests that the phase transition under study is mainly related to the ordering of octahedral groups and formation of W-O…H-N hydrogen bonds.     

Radiation Resistance of Yb:LaSc<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> and Yb:LuYSiO<Subscript>5</Subscript> Laser Crystals

The optical transmission (OT) spectra of Yb:LaSc₃(BO₃)₄ and Yb:LuYSiO₅ laser crystals have been analyzed before and after irradiation from a ⁶⁰Co source with doses up to 45 Mrad. The OT spectra of the Yb:LuYSiO₅ crystal are found to be the same (within the measurement error) before and after irradiation. The irradiation of the 10 at.%Yb:LaSc₃(BO₃)₄ crystal significantly changes its OT spectra in a wide spectral range (330 to 700 nm). A 975-nm laser based on a previously irradiated 4 at.%Yb:LuYSiO₅ crystal has exhibited a differential efficiency of 23% under diode pumping. The up-conversion luminescence spectra in the visible range of the crystals under study have been explained.     

Rectifying and photovoltage characteristics of Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>Co<Subscript>2</Subscript>O<Subscript>y</Subscript>/Nb-doped SrTiO<Subscript>3</Subscript> heterojunction

A heterojunction was fabricated by growing a layer of Bi₂Sr₂Co₂O _y thin film on the 0.7 wt% Nb-doped SrTiO₃ substrate. Such heterojunction showed good rectifying characteristics over a wide temperature range, and its transport mechanism under the forward bias can be attributed to a space charge limited conduction mechanism via defects near the interface of the heterojunction. Photovoltaic properties of the heterojunction were studied by using both continuous-wave and pulsed irradiations and the results can be well explained by the photovoltaic effect of a p–n junction.     

Mechanism of thermal decomposition of K<Subscript>2</Subscript>FeO<Subscript>4</Subscript> and BaFeO<Subscript>4</Subscript>: A review

This paper presents thermal decomposition of potassium ferrate(VI) (K₂FeO₄) and barium ferrate(VI) (BaFeO₄) in air and nitrogen atmosphere. Mössbauer spectroscopy and nuclear forward scattering (NFS) synchrotron radiation approaches are reviewed to advance understanding of electron-transfer processes involved in reduction of ferrate(VI) to Fe(III) phases. Direct evidences of Fe ^V and Fe ^IV as intermediate iron species using the applied techniques are given. Thermal decomposition of K₂FeO₄ involved Fe ^V, Fe ^IV, and K₃FeO₃ as intermediate species while BaFeO₃ (i.e. Fe ^IV) was the only intermediate species during the decomposition of BaFeO₄. Nature of ferrite species, formed as final Fe(III) species, of thermal decomposition of K₂FeO₄ and BaFeO₄ under different conditions are evaluated. Steps of the mechanisms of thermal decomposition of ferrate(VI), which reasonably explained experimental observations of applied approaches in conjunction with thermal and surface techniques, are summarized.     

Dilute ferrimagnetism of ilmenites Mn<Subscript>3</Subscript>FeTiSbO<Subscript>9</Subscript> and Mn<Subscript>4</Subscript>FeTi<Subscript>2</Subscript>SbO<Subscript>12</Subscript>

Metastable solid solutions (SS) Mn₃FeTiSbO₉ and Mn₄FeTi₂SbO₁₂ with the ilmenite structure (space group R\(\bar 3\)) have been prepared by quenching at normal conditions. The compositions of the compounds have been justified using EDX spectroscopy and X-ray diffraction. The magnetic properties of SSs have been analyzed by comparison with ferrimagnetic ilmenite Mn₂FeSbO₆ (T_N = 269 K) as a natural mineral and ceramics obtained at high pressure and high temperature. The solid solutions have been characterized as dilute magnetic systems formed as a result of substitution of nonmagnetic cations Ti⁴⁺ for a part of Fe³⁺ and Sb⁵⁺ cations. Mn₃FeTiSbO₉ is considered as a ferromagnetic with T_N = 171 K and Mn₄FeTi₂SbO₁₂ as a magnetic with the concentration of magnetic clusters below the percolation threshold.     

Differential-Thermal and X-Ray Analysis of TlFeS<Subscript>2</Subscript> and TlFeSe<Subscript>2</Subscript> Chalcogenides

Triple compounds with the formulas TlFeS₂ and TlFeSe₂ and magnetic properties are investigated via X-ray diffraction, differential-thermal, and thermogravimetric analyses. Their crystal structures are found. It is ascertained that they are described by monoclinic space group C2/m under normal conditions. The atomic coordinates and interatomic distances are determined. From differential-thermal and thermogravimetric analyses performed at temperatures of 30–900°C, it is revealed that stronger covalent bonds are implemented in TlFeS₂ crystals than in TlFeSe₂ compounds. The effects associated with energy exchange in the compounds under study are observed. The physical nature of the observed effects is discussed.