Vol 80, No 6 (2016)

The concentration dependence of the position of nodal points of a superconducting order parameter is investigated using the t–J–V model for a triangular lattice with regard to the exchange and Coulomb interactions in two coordination spheres. The conditions for a topological quantum transition are established.

AMn₃V₄O₁₂ (A = Ca, Ce, and Sm) compounds with a perovskite structure are synthesized at high pressures and temperatures. The crystalline structure of these compounds (space group \(Im\bar 3\)Z = 2) is determined via X-ray analysis. If ions in the A sublattice are changed in the order Ca²⁺–Sm³⁺–Ce³⁺, the valence is redistributed from Ca²⁺Mn₃²⁺V₄⁴⁺O₁₂ to Sm³⁺Mn₃²⁺V₄^3.75+O₁₂, and to Ce³⁺Mn₃²⁺V₄^3.75+O₁₂. The temperature dependences of the electrical resistivity are studied.

Structural transformations during reactions between nickel and an indium–tin eutectic melt are studied via the diffraction of high-energy synchrotron radiation. It is shown that InNi intermetallic compound is the first to form after melting. No phases belonging to a Ni–Sn system are observed. A hypothesis concerning the nanocluster structure of the eutectic melt is proposed: Structural formations with forbidden five-fold, seven-fold, and higher-order rotational axes of symmetry lie at the heart of nanosized clusters.

An approach for obtaining substrates of variable composition of metal systems is proposed. The spreading of drops of gallium of uniform size on the surfaces of areas of variable composition, obtained via contact melting of the Bi-Pb system is studied. A change in the diameter of a spot is observed, depending on the position of the drop on the surface of the substrate. A change in the shape of the spot is observed, depending on the composition along the interface region. The need to use force to separate the crystallized drops from the surface of the substrate, depending on the positions of the gallium drops (i.e., the substrate’s composition) confirms the wettability upon spreading.

Three types of elastic modulation in atomic layers of epitaxial Ge films on the surface of Si(111) observed in scanning tunnel microscopy are discussed. Two types of modulation are associated with misfit dislocations accumulating at the interface. Modulation of the third type arises on the surfaces of dislocation-free pseudomorphic films and could be due to the presence on a Si substrate surface of two-dimensional silicon islands with a height of three atomic bilayers and lateral dimensions of 15–20 nm. Measured bending values Δh for the third type of modulation (Δh ≤ 0.1 nm) agree with data calculated within the theory of elasticity

Refraction index dispersion in Tl_1–xAg_xGaSe₂ (0 ≤ x ≤ 0.25) crystals is investigated by studying their intrinsic interference. It is shown that there are domains with anomalous dispersion in the investigated crystals at wavelengths slightly exceeding those corresponding to exciton peaks. It is established that excitons in the crystals can be detected from their intrinsic interference at room temperature. In addition, modulation of interference patterns is observed, and a possible explanation of this phenomenon is proposed.

A statistical electron technique for calculating the interface energy at a boundary with nonpolar organic liquids is proposed in the context of the Frenkel–Gambosh–Zadumkin theory. The anisotropy of the interface energy is determined. The general dependences of the interface energies of alkali metals, copper, silver, and gold on temperature, the atomic numbers of metals, and the dielectric permeability of the organic liquid are found.

The effect iron impurities have on the low-temperature behavior of the magnetoresistance of compacted powders of CrO₂ ferromagnetic half-metal with anisotropic particle shape is investigated. The strong dependence of magnetoresistance on the spin relaxation rate during specimen magnetization reversal is revealed. It is shown that the addition of Fe impurities increases the powders’ coercive force and reduces tunnel magnetoresistance. A resonance mechanism of carrier tunneling in powders of CrO₂ solid solutions with iron impurities is proposed.

The effect applied voltage frequency has on bipolar resistive switching in microcontact type heterostructures based on thin films and single crystals of bismuth selenide is studied both experimentally and via numerical simulation.

New antiferromagnetic semiconductor compounds Tm_xMn_1–xS (0 ≤ x ≤ 0.15) with an NaCl-type FCC lattice are synthesized, and their structural, magnetic, and electrical properties are investigated at temperatures of 80–1100 K in magnetic fields of up to 10 kOe. Anomalies in the temperature dependence of resistivity in the region of magnetic transition are observed. The activation energy of the synthesized compounds is found and shown to grow along with the concentration of a substitute.

The magnetic resonance characteristics of multilayer composite nanosystems with dielectric, semiconductor, and metal nonmagnetic interlayers are investigated. Analysis of the experimental data shows that the dominant factor determining the magnetic resonance characteristics of multilayer composite nanosystems is the shape of their magnetic granules.

The effect alkali reagents have on the crystal structure of CoP films prepared via chemical deposition is investigated. It is shown that the use of sodium hydrogen carbonate and ammonium hydroxide in low concentrations leads to growth of the hexagonal phase in the films. As the concentration of alkali reagents is increased, the formation of a cubic or amorphous phase is observed.

The specific surface energy of small nanoclusters of transition fcc metals is calculated using the many-particle tight-binding potential and its earlier analog, the Gupta potential. The calculations are performed using both a theoretical model and computer simulations based on the Monte Carlo method. The equimolecular surface is considered as the dividing surface. It is found that at short radii of the nanoclusters, the surface energy and surface tension grow linearly as the particle radius increases. The values of the coefficient of proportionality in the dependence of the specific surface energy on the radius of a nanocluster are compared to the available literature data, experimental and otherwise.

The total potential energy of a crystal is presented as an expansion by irreducible interactions in clusters containing pairs of atomic triplets and quadruplets. The potential energy of the clusters in the adiabatic approximation is a function of vectors \(\vec r_{ik}\) connecting the centers of atoms in the clusters. Arguments (basic functions) affecting the potential energy of clusters are found using the model with allowance for the exchange symmetry of atoms and the irreducibility of the considered energies of doublet, triplet, and quadruplet atoms and interactions. This allows us to present arguments of the potential energy in the form of summed integral numbers (latticed sums) multiplied by a fixed value of the crystal unit cell parameter, and to set the numerical values of the potential energy arguments as a function of vectors \(\vec r_{ik}\). A potential corresponding to the thermodynamic additivity concept of crystal energy is selected as the model potential of pairwise interaction. Secondand third-order moduli of the rigidity of Co crystals with A1, A2, and HCP structures are calculated using this model of multiatom interactions.

A new size-dependent equation for an interface tension isotherm of spherical nanoparticles in the macroscopic matrix of a binary system is derived. Macroscopically, it transforms into a relationship that associates the concentrations of bulk phases. By making certain assumptions, the Ostwald–Freundlich formula for the solubility of small particles is obtained. Calculations of the interface tension for nanoprecipitates in a Fe–Cr system at 773 K show a reduction in interface tension as their dimensions shrink.

The surface tension of grain boundaries with liquid-like structure in a pure metal is presented as a function of the melting temperature and the molar volume of the metal in the solid state at the temperature of melting. Several empirical expressions for estimating the average surface tension of high-angle GBs at high homologous temperatures are proposed on this basis.

Undoped (1 – x)BiFeO₃–xPbTiO₃ binary solid solutions (0 ≤ x ≤ 0.50, Δx = 0.1) are obtained via a solid-state reaction combined with sintering in accordance with conventional ceramic technology. Features of their crystal structure formation and dielectric properties are studied in a wide range of temperatures and frequencies.

The electronic structure of SiO₂ is investigated by means of valence to core X-ray emission spectroscopy and quantum-mechanical calculations in the density functional theory approximation. Analysis of a complete set of SiK_α1, SiL_{2, 3}, and OKα X-ray emission and XPS spectra along with the calculated data provides comprehensive information on chemical interactions that occur in SiO₂.

The results from measuring the density and surface tension of Sn–In melts via the sessile drop method in a helium atmosphere and at a residual gas pressure of 0.01 Pa are presented. The density polytherms of all samples are linear with negative temperature coefficients. In the range of 550–750°C, the surface tension falls linearly as the temperature rises.