Ferromagnetic manganites La<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript>

A brief review of properties of the ferromagnetic manganites La_{1 − x} Ca _x MnO₃ is given. Lattice properties, magnetic properties, transport phenomena, magnetic resonance, and the results of neutron diffraction and optical studies are considered. Special attention is paid to effects observed near the Curie temperature.     

Magnetic properties of Ni<Subscript>3</Subscript>Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> alloys

Paramagnetic susceptibility of alloys Ni₃Al _x Mn_{1 − x} in the field of the transition between the ferromagnets described in the band theory (Ni₃Al) and in the spin-localized (Ni₃Mn) model of magnetic moments has been investigated. The concentration dependences of the paramagnetic Curie temperature, effective magnetic moment, and temperature-independent component of magnetic susceptibility have been determined.     

Structure and magnetic properties of mechanically synthesized (Fe<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>75</Subscript>C<Subscript>25</Subscript> nanocomposites

X-ray diffraction, Mössbauer spectroscopy, and magnetic measurements have been used to study the phase formation in (Fe_1–xNi_x) (with х = 0–0.20) nanocomposites upon severe plastic deformation in a planetary ball mill and subsequent annealings. It has been shown that the mechanical synthesis results in the formation of mainly a nickel-alloyed nanocrystalline (Fe, Ni)₃C cementite with a distorted crystal lattice and an amorphous Fe–Ni–C phase. During heating above 300°С, the amorphous phase crystallizes with the formation of cementite, which is characterized by a higher Ni content compared to that in mechanically synthesized cementite. The mechanically synthesized samples exhibit low coercive force (equal to several tens ampere per centimeter). In the course of annealing at temperatures of up to 500–550°С, crystal lattice distortions are removed; this results in reliving the magnetic anisotropy constant and high-coercivity state of cementite. At the same time, Ni-rich cementite areas decompose with the formation of γ-(Fe, Ni, C) phase (austenite); as a result, the average nickel content in the cementite substantially decreases. Annealings at higher temperatures cause the complete decomposition of cementite and lead to an abrupt decrease in the coercive force (Н _с) of samples. Alloying with nickel leads to an increase in the Curie temperature of cementite and a decrease in its specific saturation magnetization, coercive force, and thermal stability.     

Hyperfine-interaction parameters and magnetic phase antiferromagnet–ferromagnet transition in Ce(Fe<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>

Mössbauer spectroscopy study of Ce(Fe_1–x Si _x )₂ compounds with _x = 0 and 0.07 was performed at different temperatures. Easy magnetization axis of the CeFe₂ ferromagnet at 130 K was shown to be in the {110} plane and to deviate from the [001] axis by ～10°. Upon cooling, the Ce(Fe_0.93Si_0.07)₂ compound undergoes the ferromagnet–antiferromagnet phase transition in a temperature range of 120–125 K, which is accompanied by the reduction of the lattice symmetry. The Debye temperature of the Ce(Fe_0.93Si_0.07)₂ compound was estimated using temperature dependences of the integral intensity of Mössbauer spectrum; it is T _D ≈ 310 K. When analyzing the P(H) hyperfine field distributions P(H) derived from the Mössbauer spectra of Ce(Fe_0.93Si_0.07)₂, it was found that in the cubic structure of this compound in the ferromagnetic state there occur local rhomboherdal distortions typical of the antiferromagnetic state.     

Symmetry analysis of the magnetic structures of alloys of the quasi-binary system Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript>2</Subscript>

To estimate the reliability of the literature data on the magnetic structures of quasi-binary alloys Fe _x Mn_{1 ? x} Sn₂ obtained without using methods of symmetry analysis, we calculated the basic functions of the irreducible representations of the space group D _4h ¹⁸ (I4/mcm) with the stars of wave vectors determined from an analysis of previously published models of these structures. A comparison of these models with the results of calculations has been performed. A conclusion is made that the models of magnetic structures examined are in agreement with the results of the symmetry analysis performed in this work.     

Physical Characteristics of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>100–<Emphasis Type="Italic">x</Emphasis></Subscript> Alloys Based on Stretching and Heating Processes Using Molecular Dynamics Simulation

The physical characteristics of Ni _x Zr_100–x proportions based on stretching and heating processes were investigated using molecular dynamics (MD) simulation. The physical characteristics included axial stretching, slip vector of dislocation nucleation, radial distribution function, Poisson’s ratio, and internal energy of thermophysical properties of the Ni _x Zr_100–x proportions. The second-moment approximation for tight-binding many-body potential was used for Ni _x Zr_100–x physical characteristics during the MD simulation. Results show that the most Zr atoms of Ni _x Zr_100–x models after axis stretching obviously move and accumulate at the outside of the Ni _x Zr_100–x models due to high-temperature softening behavior and high covalent bond strength. The Poisson’s ratios of the Ni₂₀Zr₈₀, Ni₄₀Zr₆₀, Ni₅₀Zr₅₀ Ni₆₀Zr₄₀, and Ni₈₀Zr₂₀, are 0.401, 0.397, 0.490, 0.437, and 0.385, respectively. The Ni₅₀Zr₅₀ proportion has highest Poisson’s ratio, indicating that the transverse contraction strain to longitudinal extension strain is largest than others proportions. For the thermophysical properties, the atoms of Ni₅₀Zr₅₀ in solids are orientation order.     

Photovoltaic structures ITO/SiO<Subscript> <Emphasis Type="Italic">х</Emphasis> </Subscript>/<Emphasis Type="Italic">n</Emphasis>-Si of increased efficiency

Structures ITO/SiO_х/n-Si are fabricated by pulverization of solutions of indium and tin chlorides on the (100) surface of silicon wafers with resistivity 4.5 Ω cm. The influence of the state of the Si surface on the efficiency of structures as photoelectric converters is investigated. It is shown that structures with an unetched surface of silicon wafers are the most efficient. Solar cells based on studied ITO/SiO_х/n-Si structures with an inverse layer demonstrate an efficiency close to 16% in AM 1.5 conditions.     

Electrodeposition Process and Performance of CuIn(Se<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>S<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript> Film for Absorption Layer of Thin-Film Solar Cells

CuIn(Se _x S_1?x )₂ thin film is prepared by the electrodeposition method for the absorption layer of the solar cell. The CuIn(Se _x S_1?x )₂ films are characterized by cyclic voltammetry measurement for the reduction of copper, indium, selenium and sulfur in selenium and sulfur in aqueous solutions with sodium citrate and without sodium citrate. In the four cases, the defined reduction process for every single element is obtained and it is observed that sodium citrate changes the reduction potentials. A linear relationship between the current density of the reduction peak and (scan rate v)^1/2 for copper and indium is achieved, indicating that the process is diffusion controlled. The diffusion coefficients of copper and indium ions are calculated. The diffusional coefficient D value of copper is higher than that of indium, and this is the reason why the deposition rate of copper is higher. When four elements are co-deposited in the aqueous solution with sodium citrate, the quaternary compound of CuIn(Se _x S_1?x )₂ is deposited together with Cu₃Se₂ impure phases after annealing, as found by XRD spectra. Morphology is observed by SEM and AFM. The chemical state of the films components is analyzed by XPS. The UV-Visible spectrophotometer and electrochemistry workstation are employed to measure the photoelectric properties. The results show that the smooth, uniform and compact CuIn(Se _x S_1?x )₂ film is a semiconductor with a band gap of 1.49 eV and a photovoltaic conversion efficiency of 0.45%.     

Correlation between the Hall Resistance and Magnetoresistance in the Mixed State of an Nd<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>4 + δ</Subscript> Electronic Superconductor

The Hall resistance and the magnetoresistance in the mixed state of the Nd_{2 ? x}Ce _x CuO_{4 + δ} quasi-two-dimensional system near the antiferromagnetic-superconductor (AF-SC) phase transition have been measured at doping levels x = 0.14 and 0.15, and a correlation has been established. This correlation can be analyzed using the following power relationship: ρ _xy (B) ~ [ρ _xx (B)]^β. It was found that index β varied from 0.94 ± 0.03 in the region of AF and SC coexistence (x = 0.14) to 0.6 ± 0.1 in the SC region with the maximum critical temperature (x = 0.15) at low temperatures and weak magnetic fields. This reduction suggests that the symmetry of carrier pairing changes at the boundary of the transition from the phase of antiferromagnetic ordering and spin density waves to the superconducting phase in the presence of antiferromagnetic spin fluctuations.     

Optical Parameters of Spray-Deposited CdS<Subscript>1−<Emphasis Type="Italic">y</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> Thin Films

CdS _x Te_1?x and CdS_1?y Te _y solid solutions are usually formed in the interfacial region in CdS/CdTe solar cells during the deposition of the CdTe layer and/or the processing steps of the device. In this work, indium-doped CdS_1?y Te _y thin films were prepared by first producing CdS:In thin films by the spray pyrolysis technique on glass substrates, then annealing the films in nitrogen atmosphere in the presence of elemental tellurium. The films were characterized by scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmittance measurements. The transmittance was used to deduce the reflectance from which the optical parameters were computed. The extinction coefficient, refractive index, the real and imaginary parts of the dielectric constant, optical conductivity, and energy loss were computed, and their dependence on the composition was investigated. In addition, the dispersion of the refractive index was analyzed by the single oscillator model, and dispersion parameters were investigated.     

Effects of Na/K ratio on the phase structure and electrical properties of Na<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>K<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>NbO<Subscript>3</Subscript> lead-free piezoelectric ceramics

Lead-free piezoelectric NaxK1-xNbO3(x = 0.3-0.8)(NKN) ceramics were fabricated by normal sintering at 1060°C for 2 h.Microstructures and electrical properties of the ceramics were investigated with a special emphasis on the influence of Na content.The grain size of the produced dense ceramic was decreased by increasing Na content.A discontinuous change in the space distance was found at the composition close to Na0.7K0.3NbO3 ceramic, which indicates the presence of a transitional composition between two dif...     

1:13 phase formation mechanism and first-order magnetic transition strengthening characteristics in (La,Ce)Fe<Subscript>13–<Emphasis Type="Italic">x</Emphasis></Subscript>Si<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> alloys

The effects of the introduction of Ce to La_1?x Ce _x Fe_11.5Si_1.5 alloys on 1:13 phase formation mechanism, the first-order magnetic phase transition strengthening characteristics, and magnetocaloric property were studied, respectively. The results show that the formation mechanisms of 1:13 and LaFeSi phases in La_1?x Ce _x Fe_11.5Si_1.5 alloys are the same as those of Ce₂Fe₁₇ and CeFe₂ phases in Ce–Fe binary system, respectively. The substitution of Ce in 1:13 phase which is limited can make the first-order magnetic phase transition characteristics strengthen, which can make thermal and magnetic hysteresis increase, the temperature interval of temperature-induced phase transition decrease, and the critical magnetic field of field-induced magnetic phase transition (H _C) increase, respectively. Owing to the lattice shrink of 1:13 phase with the increase in Ce content, the Curie temperatures (T _C) show a linear decrease. The maximum change in magnetic entropy gradually increases due to the decrease in temperature interval of temperature-induced phase transition, but the relative cooling capacities are all about 80 J·kg^?1 at magnetic field of 2 T.     

Transport properties of solid solutions of <Emphasis Type="Italic">х</Emphasis>KYF<Subscript>4</Subscript>–(1–<Emphasis Type="Italic">х</Emphasis>)PbF<Subscript>2</Subscript> system

In the system (1–x)PbF_2–x YF_3–x KF, solid solutions of aliovalent substitution with fluorite structure at 0.47 < x < 0.69 are formed, in which the fluorine ions are found to be in three structurally nonequivalent positions that differ in the local environment and mobility. There are immobile, locally mobile, and highly mobile anions. The conductivity of the synthesized polycrystalline samples is ensured by highly mobile interstitial fluoride ions, whose concentration and hence electrical conductivity increase on heating. The contribution of the surface conductivity of crystallites is not detected. The electronic component is two orders of magnitude lower than the ionic one.     

Optimizing Thermoelectric Properties of In Situ Plasma-Spray-Synthesized Sub-stoichiometric TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> Deposits

In this article, an attempt has been made to relate the thermoelectric properties of thermal spray deposits of sub-stoichiometric titania to process-induced phase and microstructural variances. The TiO_2?x deposits were formed through the in situ reaction of the TiO_1.9 or TiO_1.7 feedstock within the high-temperature plasma flame and manipulated via varying the amounts of hydrogen fed into in the thermal plasma. Changes in the flow rates of H₂ in the plasma plume greatly affected the in-flight particle behavior and composition of the deposits. For reference, a high-velocity oxy-fuel spray torch was also used to deposit the two varieties of feedstocks. Refinements to the representation of the in-flight particle characteristics derived via single particle and ensemble diagnostic methods are proposed using the group parameters (melting index and kinetic energy). The results show that depending on the value of the melting index, there is an inverse proportional relationship between electrical conductivity and Seebeck coefficient, whereas thermal conductivity has a directly proportional relationship with the electrical conductivity. Retention of the original phase and reduced decomposition is beneficial to retain the high Seebeck coefficient or the high electrical conductivity in the TiO₂ system.     

Optical absorption and structure of energy bands of GdNi<Subscript>5 − x</Subscript>Cu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> intermetallic compounds

Optical properties of intermetallic compounds GdNi_{5 ? x} Cu _x (x = 0, 0.5, 1, 1.5, and 2) have been studied in a spectral range from 0.22 to 15 μm using the ellipsometry method. The substitution of copper for nickel has been found to lead to local changes in the interband optical conductivity spectra. A new quantum-absorption band, whose intensity increases substantially with increasing copper content, has been found at 3–4 eV. The relaxation and plasma frequencies of conduction electrons, which were calculated using data on the optical parameters, also depend on the concentration. Self-consistent calculations of the electronic structure of the intermetallic binary GdNi₅ compound have been performed using the LSDA + U method. The density of electronic states for two spin projections and the frequency dependence of the interband optical conductivity of the compound have been calculated.     

Effect of Si and Y<Subscript>2</Subscript>O<Subscript>3</Subscript> Additions on the Oxidation Behavior of Ni–<Emphasis Type="Italic">x</Emphasis>Al (<Emphasis Type="Italic">x</Emphasis> = 5 or 10 wt%) Alloys at 1150 °C

The effect of Si and Y₂O₃ additions on the oxidation behavior of Ni–xAl (x = 5 or 10 wt%) alloys at 1150 °C was studied. The addition of Y₂O₃ accelerates oxidation rate of alloys, especially growth rate of NiO, but improves adherence of the scale to the substrate. The addition of Si facilitates the selective oxidation of Al, suppresses the formation of NiO and therefore reduces the critical Al content to form continuous layer of alumina scale. Higher Al content decreases the oxidation rate of alloys in binary Ni–Al alloys and increases the oxidation rate of alloys in ternary Ni–Al–Si alloys. The effect of third-element Si is more significant and beneficial than that of Al content in ternary Ni–Al–Si alloys.     

Microstructure and plastic deformation of orthorhombic titanium aluminides Ti<Subscript>2</Subscript>AlNb. III. Formation of transformation twins upon the <Emphasis Type="Italic">B</Emphasis>2 → <Emphasis Type="Italic">O</Emphasis> phase transformation

X-ray diffraction and transmission electron microscopy were used to study the O-phase formation in the Ti-25.6% Al-13.9% Nb-0.3% Mo-0.3% Zr alloy upon the B2 → O phase transformation. The formation of pseudotwins is shown to be possible in the B2 phase in the Ti-Al-Nb alloys. It is found that the O phase upon the B2 → O phase transformation does not undergo twinning, and all twins observed in the alloy belong to the intermediate metastable B19 phase. The orthorhombic O phase is formed upon ordering inside the B19-phase twins and save their boundaries.     

Performance of Sm<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>CoO<Subscript>3−<Emphasis Type="Italic">δ</Emphasis></Subscript> membrane under CO<Subscript>2</Subscript>-containing atmosphere

The permeability and stability of Sm_0.7Sr_0.3CoO_3?δ (SSCO) regarding the special requirements for carbon capture and storage (CCS) application were investigated. Pure CO₂ was used as the sweep gas at 900 °C, leading to that the oxygen permeation flux decreases by about 34 %. Several cycles of changing the sweep gas between helium and CO₂ indicate the good reversibility of this degradation. Both carbonate formation and adsorption of CO₂ on the membrane surface are responsible for the degradation of the membrane performance. The better CO₂ resistance results from the substitution of Sm for Sr due to the higher acidity of Sm₂O₃ (1.278) than that of SrO (0.978) and a discontinuous layer of carbonate.     

Prospects of In-Situ <Emphasis Type="Italic">α</Emphasis>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> as an Inoculant in Aluminum: A Feasibility Study

In-situ α-Al₂O₃ was successfully synthesized and dispersed in Al alloy using B₂O₃ and ultrasonication-aided liquid mixing technique. Microstructure analysis identified α-Al₂O₃ as the most common phase in the composite master alloy, whereas AlB₁₂ was frequently observed and AlB₂ was rarely found in the alloy. Grain refinement analysis of selected Al alloys registered a transition of columnar to equiaxial grains of α-Al with the inoculation of the master alloy and ultrasonication treatment. Similarly, an improvement in the mechanical properties of A357 alloy was observed with the combination of inoculation and ultrasonication treatment.     

Restoration of the structure and superconducting properties of Ba<Subscript>2</Subscript>YCu<Subscript>3</Subscript>O<Subscript>7 − <Emphasis Type="Italic">δ</Emphasis></Subscript> after low-temperature decomposition

A study of the restoration of the structure and superconducting properties of the nonstoichiometric Ba₂YCu₃O_{7 ? δ} with different oxygen contents after low-temperature decomposition at T = 200 and 300°C has been carried out. It has been shown that the annealing of the decomposed samples at temperatures higher than the decomposition range (e.g., at 400–900°C) does not lead to the complete restoration of the structure because of the presence of defects in the cation sublattices, which appear in the course of decomposition. The degree of restoration is less, the greater the degree of decomposition. An analogy has been revealed between the structure and properties of samples which underwent low-temperature decomposition and were subjected to irradiation by high-energy particles; a similar structure was found in ceramics synthesized at reduced temperatures (<900°C).