Specific features of the structure,magnetic properties,and heat capacity of intercalated compounds Cr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>TiSe<Subscript>2</Subscript>

Structural features, magnetic properties, and heat capacity of Cr _x TiSe₂ intercalated compounds with a layered structure have been studied experimentally for 0 ≤ x ≤ 0.5. It is shown that, at high chromium concentrations (x > 0.25), the magnetic properties of the compounds are strongly affected by the degree of ordering and distribution pattern of the intercalated atoms. Depending on the cooling rate of samples of the same composition (x = 0.5), an antiferromagnetic or a cluster-glass-type state can be obtained. Heat capacity measurements have revealed a nonmonotonic variation in the lattice rigidity with increasing concentration of intercalated atoms.     

X-ray reflectivity and photoelectron spectroscopy of superlattices with silicon nanocrystals

The structural properties and features of the chemical composition of SiO _x N _y /SiO₂, SiO _x N _y /Si₃N₄, and SiN _x /Si₃N₄ multilayer thin films with ultrathin (1–1.5 nm) barrier SiO₂ or Si₃N₄ layers are studied. The films have been prepared by plasma chemical vapor deposition and have been annealed at a temperature of 1150°С for the formation of silicon nanocrystals in the SiO _x N _y or SiN _x silicon-rich layers with a nominal thickness of 5 nm. The period of superlattices in the studied samples has been estimated by X-ray reflectivity. The phase composition of superlattices has been studied by X-ray electron spectroscopy using the decomposition of photoelectron spectra of the Si 2p, N 1s, and O 1s levels into components corresponding to different charge states of atoms.     

Effect of doping by boron,carbon, and nitrogen atoms on the magnetic and photocatalytic properties of anatase

The effect of doping of titanium dioxide with the anatase structure by boron, carbon, and nitrogen atoms on the magnetic and optical properties and the electronic spectrum of this compound has been investigated using the ab initio tight-binding linear muffin-tin orbital (TB-LMTO) band-structure method in the local spin density approximation explicitly including Coulomb correlations (LSDA + U) in combination with the semiempirical extended Hückel theory (EHT) method. The LSDA + U calculations of the electronic structure, the imaginary part of the dielectric function, the total magnetic moments, and the magnetic moments at the impurity atoms have been carried out. The diagrams of the molecular orbitals of the clusters Ti₃ X (X = B, C, N) have been calculated and the pseudo-space images of the molecular orbitals of the clusters have been constructed. The effect of doping on the nature and origin of photocatalytic activity in the visible spectral range and the specific features of the generation of ferromagnetic interactions in doped anatase have been discussed based on the analysis of the obtained data. It has been shown that, in the sequence TiO_{2 ? y} N _y → TiO_{2 ? y} C _y → TiO_{2 ? y} B _y (y = 1/16), the photocatalytic activity can increase with the generation of electronic excitations with the participation of impurity bands. The calculated magnetic moments for boron and nitrogen atoms are equal to 1 μ_B, whereas the impurity carbon atoms are nonmagnetic.     

Multicomponent <Emphasis Type="Italic">n</Emphasis>-(Bi,Sb)<Subscript>2</Subscript>(Te,Se,S)<Subscript>3</Subscript> solid solutions with different atomic substitutions in the Bi and Te sublattices

The thermoelectric properties of n-Bi_{2 ? x} Sb _x Te_{3 ? y ? z} Se _y S _z solid solutions are studied in the temperature range 300–550 K. It is shown that an increase in the parameter β determining the figure-of-merit Z of the material is observed in compositions with the optimally related effective mass of the density of states m/m ₀, the carrier mobility μ₀, and the lattice thermal conductivity κ _L . Within the temperature range 300–350 K, the parameter β and the figure-of-merit Z are found to increase in solid solutions with substitutions in both bismuth telluride sublattices Bi → Sb and Te → Se, S (x = 0.16, y = z = 0.12) for optimum electron concentrations. An increase in the electron concentration and substitutions of atoms only in the tellurium sublattice bring about an increase in the β parameter and the value of Z at higher temperatures. Within the range 350–450 K, the parameters β and Z are observed to increase in a solid solution with a low content of substituted atoms in the tellurium sublattice Te → Se, S for y = z = 0.09 and, at higher temperatures up to 550 K, in compositions with tellurium substituted by selenium only, with increasing content of substituted atoms.     

Extreme Electromechanical Characteristics and Microstructural Features of Ferro-Piezoceramics Based on Lead Titanate

Microstructural features and electrophysical parameters of a number of solid solutions based on PbTiO₃ are investigated. Solid solutions (Pb_{1–3/2x + z/2}Nd _x )(Ti_1–y–zMn _y Inz)O₃ and Pb_1–xCa _x Ti_1–y(W_1/2Co_1/2) _y O₃ with extreme values of the mechanical Q-factor and electromechanical anisotropy are chosen as the objects of investigation. The ferro-piezoceramic samples are obtained through conventional sintering and hot pressing. X-ray structural and microstructural studies are performed, and the complex elastic, dielectric, and piezoelectric parameters of experimental samples are measured. The frequency dependences of complex parameters of the experimental samples have been studied at frequencies of up to 40 MHz. It is established that the extreme values of the mechanical Q-factor and piezoelectric anisotropy of the investigated PbTiO₃-based solid solutions are due to microstructural features associated with the technological regimes of ferropiezoceramic fabrication.     

An Ab Initio Study of the Structural and Electronic Properties of the Low-Defect TiC(110) Surface Simulating Oxygen Adsorption after Exposure to Laser Plasma

An ab initio simulation of the adsorption of atomic oxygen on the low-defect titanium carbide (110) surface reconstructed by laser radiation was performed. The relaxed atomic structures of the (110) surface of the O/Ti _x C _y system with Ti and C vacancies observed during the thermal treatment were studied in terms of the density functional theory. DFT calculations of their structural, thermodynamic, and electronic properties were performed. The bond lengths and adsorption energies were determined for various reconstructions of the atomic structure of the O/Ti _x C _y (110) surface. The effects of the oxygen adatom on the band and electronic spectra of the O/Ti _x C _y (110) surface were studied. The effective charges on the titanium and carbon atoms surrounding the oxygen atom in various reconstructions were determined. The charge transfer from titanium to oxygen and carbon atoms was found, which is determined by the reconstruction of the local atomic and electronic structures and correlates with chemisorption processes. The potential mechanisms of laser nanostructuring of the titanium carbide surface were suggested.     

Equilibrium magnetic and orbital states of the manganites with four manganese atoms in the unit cell

The carrier energy spectrum and the total energy of various magnetic and orbital crystal-structure configurations of the manganites R _1?x A _xMnO₃ (R=La, Pr, Nd, Sm, etc.; A=Ca, Sr, Ba) with four manganese atoms in the unit cell have been calculated for the electron doping region x>0.5. The equilibrium magnetic and orbital configurations of the model are determined by minimizing the total energy of the system with respect to the angles θ _i ^s , φ_i, and θ _i ^o , which define the directions of the local manganese magnetic moments and the type of orbital mixing of the e _g electrons in the manganites. Assuming the parameters of the Heisenberg exchange interaction to be 0.018t<J _AFM<0.022t, the Hund exchange interaction to be J _H=2.5t, and the Jahn-Teller splitting to be Δ=1.5ty, the model with four manganese atoms in the unit cell predicts the experimentally observed magnetic phase alternation sequence G-C-A with increasing doping level y=1?x. For the values J _AFM<0.018t and y<0.28, this model allows the existence of a collinear phase H not observed earlier.     

Investigation of the cation distribution in perovskite-like oxides with Mössbauer spectroscopy

Complex perovskite-like oxides, such as LnFe_2/3Mo_1/3O₃ orthoferrites, Ln_8?ySr_yCu_8?xFe_xO₂₀ (8-8-20), Pr₄BaCu₄FeO_13-δ(4-1-5), YBa_2-yLa _y Cu_3-xFe _x O_7-δ and Y_1-yCa _y Ba _y La _y Cu_3-xFe _x O_7-δ (1-2-3), are studied by means of Mössbauer spectroscopy. At room temperature, the spectra of the orthoferrites contain only magnetic components. The spectra of the 1-2-3 compounds contain only magnetically disordered components: iron atoms substitute for copper at Cu(1) sites, taking various configurations: planar squares, quadratic pyramids, and octahedra. Cuprates 8-8-20 and 4-1-5 have a wide diversity of spectra. In the 8-8-20 oxides, a phase related to the pyramidal environment of the iron cations is present at any iron concentration. In all the perovskites, iron cations become magnetically ordered only at octahedral sites of the structure.     

Synthesis,structure, and properties of BIFENBVOX

Solid solutions Bi₄V_2-x Fe _x/2Nb _x/2O_11-δ (х?=?0.05–1.0) and Bi₄V_2-х-y Fe _x Nb _y O_11–δ (with fixed x or y?=?0.2 and variable х or y?=?0.2–0.5 with step 0.1) were synthesized by the standard ceramic technology in the temperature range 773–1113 K and by mechanochemical activation method using Bi₂O₃, V₂O₅ Fe₂O₃, and Nb₂O₅ oxides as initial compounds. The formation of solid solutions was studied. Ranges of stability and temperature values of phase transitions for different polymorphous modifications were defined using dylatometric and thermo gravimetric studies. The morphology and the local chemical composition of the ceramic samples were studied. Samples with concentration of dopants x?>?0.3 contain two phases; both major and impurity phases are solid solutions of the BIFENBVOX type although the dopants atoms distribution between them is random. The thermal expansion coefficients (TEC) were measured. The electrical conductivity of ceramic samples was investigated in a wide range of temperatures. The highest conductivity values among the studied solid solutions are observed for the sample with a small amount of dopants x?=?0.25.     

Spectroscopy of optical centers of Eu<Superscript>3+</Superscript> ions in partially stabilized and stabilized zirconium crystals

The structure of the optical centers of Eu³⁺ ions in tetragonal (ZrO₂)_1–x–y (Y₂O₃) _x (Eu₂O₃) _y (х = 2.7–3.6; y = 0.1) and cubic (ZrO₂)_1–x–y (Y₂O₃) _x (Eu₂O₃) _y (х = 8–38; y = 0.1–0.5) crystals of solid solutions on the basis of zirconium dioxide is studied using the methods of optical and Raman-scattering spectroscopy. Characteristic optical centers of Eu³⁺ ions with different crystalline environments are revealed in the above compounds.     

Microhardness and refractive index of titanium dioxide-based binary coatings

Glass composites covered by sol–gel TiO₂–m Me _x O _y (Me _x O _y = ZnO, CdO, SnO, CuO, and Fe₂O₃ and m = 2, or 10 wt %) binary oxide coatings have been studied. The microhardness of the composites and glass substrate has been measured, and the microhardness of the coatings has been determined from these measurements. A correlation between the microhardness of the coatings, their refractive index, and packing density of disperse sol phase particles in the coating has been established.     

Effect of chromium and tellurium impurities on the thermoelectric parameters of galena

Concentration dependences of the Seebeck coefficient, resistivity, and thermal conductivity of thermoelectric PbS crystals with chromium (0 < x ≤ 0.01) and tellurium (0 < y ≤ 0.03) impurities are examined in the temperature region of 300–800 K. It is shown that the introduction of chromium increases the number of free electrons in PbCr _x S _1–x crystals and reduces the Seebeck coefficient. However, an increase in the concentration of tellurium in PbCr _x S _1–x–y Te _y alloys raises the Seebeck coefficient while simultaneously reducing the thermal conductivity. As a result, the thermoelectric efficiency of PbCr _x S _1–x–y Te _y crystals increases. The reasons for the observed effects are discussed.     

The Partition Formalism and New Entropic-Information Inequalities for Real Numbers on an Example of Clebsch–Gordan Coefficients

We discuss the procedure of different partitions in the finite set of N integer numbers and construct generic formulas for a bijective map of real numbers s _y , where y = 1, 2,…, N, N = \( \underset{k=1}{\overset{n}{\varPi}}{X}_k, \) and X _k are positive integers, onto the set of numbers s(y(x ₁, x ₂,…, x _n )). We give the functions used to present the bijective map, namely, y(x ₁, x ₂, …, x _n ) and x _k (y) in an explicit form and call them the functions detecting the hidden correlations in the system. The idea to introduce and employ the notion of “hidden gates” for a single qudit is proposed. We obtain the entropic-information inequalities for an arbitrary finite set of real numbers and consider the inequalities for arbitrary Clebsch–Gordan coefficients as an example of the found relations for real numbers.     

Ferroelectric phase transitions in ionic conductors based on bismuth vadanate

Ceramic solid solutions (Bi_{1 ? x} La _x )₄V₂O_{11 ? z} (I), Bi₄(V_{1 ? x} Fe _x )₂O_{11 ? y} (II), and (Bi_{1 ? x} La _x )₄(V_0.96Fe_0.04)₂O_{11 ? y} (III) (x = 0–0.3, step Δx = 0.02) are prepared using solid-phase synthesis. The concentration and temperature ranges of stabilization of different polymorphic modifications, including the ranges of concentrations x corresponding to the stabilization of the ferroelectric phase, are established. It is revealed that an increase in the concentration x in the region of existence of the pseudoorthorhombic phase α of the solid solutions studied leads to a decrease in the transition temperature, smearing of the transition, and an increase in the width of the thermal hysteresis of the ferroelectric phase transition. The effect of compressing of the domain walls by oxygen vacancies was revealed in the samples from the region of existence of the ferroelectric α phase, and the effect of dielectric relaxation was detected in the samples from the region of existence of the orthorhombic phase β.     

Dielectric properties of CuInP<Subscript>2</Subscript>(Se<Subscript>x</Subscript>S<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>6</Subscript> solid solutions

The dielectric properties of layered crystals of CuInP₂(Se_xS_1?x)₆ solid solutions are studied at x = 0.02, 0.05, 0.20, and 0.40. At a low selenium content (x ≤ 0.05), the solid solutions undergo a transition to the phase with short-range polar order. This transition manifests itself as a diffuse maximum in the temperature dependence of the permittivity ε′(T). Ferroelectric ordering in the solid solutions under investigation is suppressed at x > 1. It is assumed that the structural disordering initiated by the substitution of atoms in the anion sublattice of the solid solutions at 0.1 < x < 0.75 leads to the formation of the state of structured glass. The dielectric relaxation dispersion observed in the radio-frequency range at temperatures of 80–140 K is associated with the freezing of the relaxation dynamics of individual copper atoms.     

Structural and compositional heterogeneities in liquid aluminosilicate: insight from a grain structure model

Network structure as well as structural and compositional heterogeneities in aluminosilicate (Al₂O₃-2SiO₂) under compression is investigated by analysis and visualization of simulation data. Structural and compositional heterogeneities are clarified through analysis of topology structure and size distribution of TO _x -clusters (T = Si, Al; x = 3, 4, 5, 6) as well as OT _y -clusters (y = 2, 3, 4). The TO _x -cluster can be considered as TO _x -grains. It appears that the structure of aluminosilicate is the mixture of TO _x -grains with a different short-range order structure and this is the origin of structural heterogeneity. Regarding their composition, the OSi _y - and OAl _y -clusters can be considered as silica- and alumina-grains respectively, and the structure of aluminosilicate can thus be considered to be formed from silica- and alumina-grains. This results in compositional heterogeneity. Moreover, the degree of polymerization and polyamorphism as well as dynamic heterogeneity is also discussed in detail.     

The Nernst-Ettingshausen coefficient in the normal phase of doped HTSCs of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>y</Subscript> system

The temperature dependence of the Nernst-Ettingshausen coefficient Q(T) in the normal phase of doped HTSCs of the yttrium system was studied. The main features characterizing the behavior of this coefficient were revealed, and the character and mechanism of the effect that various nonisovalent substituents exert on the Q(T) dependence were analyzed. It is shown that the narrow-band model permits one not only to describe all the specific features observed in the Q(T) curves but also to perform a simultaneous quantitative analysis of the temperature dependences of four kinetic coefficients (the electrical resistivity and the Seebeck, Hall, and Nernst-Ettingshausen coefficients) with the use of a common set of model parameters characterizing the band structure and carrier system in the normal phase of an HTSC. This approach was employed to determine the carrier mobilities and the asymmetry of the dispersion curve in the systems studied (YBa₂Cu₃O_y, y = 6.37–6.91; YBa₂Cu_3?xCo_xO_y, x = 0–0.3; Y_1?xCa_xBa₂Cu₃O_y, x = 0–0.25; Y_1?xCa_xBa_2?xLa_xCu₃O_y, x = 0–0.5) and to analyze the effect of the substitutions involved on the variation of these parameters.     

Synthesis and vibrational spectra of solid solutions based on lanthanum gallate

The synthesis conditions for single-phase solid solutions based on lanthanum gallate, LaGa_{1 ? x} Mg _x O_{3 ? δ}(x= 0–0.25, solid-phase method) and La_{1 ? y}Sr_yGa_{1 ? y}Mg_yO_{3 ? δ}(y= 0–0.2, glycine nitrate method), have been investigated. The structural parameters have been calculated using X-ray powder diffraction data. The IR and Raman spectra have been analyzed. Regularities in the changes in the structural parameters and vibrational spectra with composition are established.     

Electronic effect of doped oxygen atoms in Bi2201 superconductors determined by scanning tunneling microscopy

Oxygen dopants are essential for tuning the electronic properties of the cuprate superconductors Bi_2Sr_2Ca_(n-1)Cu_nO_(2n+4+δ).Here,we study an optimally doped Bi_2Sr_(2-x)La_xCuO_(6+δ)and an overdoped Bi_(2-y)Pb_ySr_2CuO_(6+δ)by scanning tunneling microscopy and spectroscopy(STM/STS).Based on the characteristic features of local STS,three forms of oxygen dopants are identified:interstitial oxygen atoms on the SrO layers,oxygen vacancies on the SrO layers,and interstitial oxygen atoms on the BiO layers.In both samples,the first form dominates the number of oxygen dopants.From the extracted spatial distribution of the oxygen dopants,we calculate the dopant concentrations and estimate the average hole carrier density.The magnitudes of the electronic pseudogap state in both samples are inhomogeneously distributed in space.The statistical analysis on the spatial distributions of the oxygen dopants and the pseudogap magnitude demonstrates that the doped oxygen atoms on the SrO layers tend to suppress the nearby pseudogap magnitude.     

Single-crystalline M-type Sr Hexaferrites studied by <Superscript>57</Superscript>Fe Mössbauer spectroscopy

The ⁵⁷Fe Mössbauer spectra of the single crystalline and the finely ground Sr_1?x La _x Fe_12?y Co _y O₁₉ (x = 0 : y = 0, x = 0.192 : y = 0.152 and x = 0.456 : y = 0.225) samples have been measured to investigate the La-Co substitution effects. All observed spectra at 150 K were well fitted using the five subspectra which correspond to the five crystallographical nonequivalent Fe sites in the M-type hexaferrite, indicating that the valence changes to Fe²⁺ ions in the Fe³⁺ ions were not observed in our Sr_1?x La _x Fe_12?y Co _y O₁₉ samples. In SrFe₁₂O₁₉, the relative absorption intensities in the five subspectra show the large anisotropies in the recoilless fractions at the five Fe sites whereas these anisotropies were not observed in Sr_0.544La_0.456Fe_11.775Co_0.225O₁₉. These results indicate the chemical compositional dependence on the anisotropies of the recoilless fractions at the five Fe sites. The substitution of a Co²⁺ ion for the Fe³⁺ ion changes the center shifts of the Fe³⁺ ions near the Co²⁺ ion by the perturbation of the Fe-O-Co hybridizations. Therefore, the Co²⁺ ions occupy the 4f ₁ and the 4f ₂ sites due to the chemical compositional dependences of the refined magnetic hyperfine field and center shifts of the Fe³⁺ ions.