卷 60, 编号 10 (2018)

The density functional method with pseudopotentials are used to study the electron states of nanoparticles and nanostructured systems: chains, films, and three-dimensional nanosystems of titanium and zirconia. It is shown that all studied titanium nanosystems have the density of electronic states (DES) of the metallic type, but zirconia nanosystem demonstrates a dielectric energy gap in the vicinity of the Fermi level. The density of states of nanostructured titanium is close in shape to DES of the single crystal but has a smoother shape due to disordering of the atomic arrangement. The forbidden band width of the nanostructured zirconia is smaller as compared to the corresponding width in crystalline ZrO₂, supposedly because of incomplete saturation of ionic bonds.

The energy of grain boundary shears is calculated for symmetric grain boundaries (GBs) using ab initio methods and molecular-dynamic modeling in order to elucidate mechanisms that control GB shear-migration coupling in typical symmetric GBs, such as Σ3 (111), Σ5 (012), Σ5 (013) and Σ11 (113) tilt GBs, in Al bicrystal. The energy of generalized grain-boundary stacking faults (GB–SF) is determined, and the preferred directions and the energy barrier are established for grain-boundary slippage. It is shown that the relative slippage of neighboring grains at certain directions of particle shears is accompanied by conservative migration of GB in the direction perpendicular to its plain. The modeling data are comparative to known grain-boundary shear-migration coupling mechanisms in Al.

The problem of establishing the correlation between, on the one hand, the chemical and phase compositions of Ni_1–xW_x alloys (0 ≤ x ≤ 0.5) and, on the other hand, the character of the temperature dependences of the electrical resistivity, is considered. Based on the experimental ρ(T) curves, the concentration dependences of are reconstructed in the wide temperature range (50 K ≤ T ≤ 273 K). The ρ(x) curves have features related to a change in the crystal structures of the alloys (concentration fcc–bcc phase transition), their magnetic structures and percolation processes occurring in the two-phase fcc + bcc medium.

Samples of a superconducting indium nanocomposite based on a thin-film porous dielectric matrix prepared by the Langmuir–Blodgett method are obtained for the first time, and their low-temperature electrophysical and magnetic properties are studied. Films with thickness b ≤ 5 μm were made from silicon dioxide spheres with diameter D = 200 and 250 nm; indium was introduced into the pores of the films from the melt at a pressure of P ≤ 5 kbar. Thus, a three-dimensional weakly ordered structure of indium nanogranules was created in the pores, forming a continuous current-conducting grid. Measurements of the temperature and magnetic field dependences of the resistance and magnetic moment of the samples showed an increase in the critical parameters of the superconductivity state of nanostructured indium (critical temperature T_c ≤ 3.62 K and critical magnetic field H_c at T = 0 K H_c(0) ≤ 1700 Oe) with respect to the massive material (T_c = 3.41 K, H_c(0) = 280 Oe). In the dependence of the resistance on temperature and the magnetic field, a step transition to the superconductivity state associated with the nanocomposite structure was observed. A pronounced hysteresis M(H) is observed in the dependence of the magnetic moment M of the nanocomposite on the magnetic field at T < T_c, caused by the multiply connected structure of the current-conducting indium grid. The results obtained are interpreted taking into account the dimensional dependence of the superconducting characteristics of the nanocomposite.

In this paper, we compared the results of a heat capacity study of an erbium-doped gallium gadolinium garnet crystal with data for an undoped garnet. The measurements were carried out in the temperature range from 1.9 to 220 K and in magnetic fields from 0 to 9 T. The temperature dependences of the specific heat were interpreted with allowance for the Schottky contributions due to the Gd³⁺ and Er³⁺ ions and the contributions of the thermal vibrations of the crystal lattice. The values of entropy and magnetic entropy are calculated.

The results of studies of the absorption spectra of nickel orthoborate Ni₃(BO₃)₂ in the range of electronic d–d-transitions are reported. The obtained data are analyzed in the framework of the crystal field theory. The Ni²⁺ ions are located in two crystallographically nonequivalent positions 2a and 4f with point symmetry groups C_2h and C₂, respectively, surrounded by six oxygen ions forming deformed octahedra. The absorption spectra exhibit three intense bands corresponding to spin-resolved transitions from the ground state of nickel ion ³A_2g (³F) to the sublevels of the ³T_2g (³F), ³T_1g (³F) and ³T_1g (³P) triplets split by the spinorbit interaction and the rhombic component of the crystal field. At temperatures below 100 K, the spectra exhibit a thin structure, in which phonon-free lines can be distinguished. Comparison of the calculated frequencies of the zero-phonon transitions with the experimental data allows estimating parameters of the crystal field acting on the nickel ions in the 2a- and 4f-positions, as well as the parameters of electrostatic interaction between the 3d electrons and spin-orbit interaction constants.

The detection conditions and features of direct and scattered neutron wave interference are studied on magnetized Co₆₇Fe₃₁V₂ alloy slabs. The angular intensity distributions of neutrons passed through a sample are measured for the opposite polarization directions of the initial neutron beam. The sought-for effect that is induced by the magnetic scattering on crystal structure irregularities in specimens manifest itself by different areas of peaks “without neutron spin flip.” The ratio of these areas depends on the thermal treatment mode, sample thickness and strength of the magnetic field applied to the sample. The peaks “with neutron spin flip” are due to the mechanism of neutron wave passage through magnetononcollinear boundaries. The methods for experimental data acquisition and processing are reported as well.

Phase states of an isotropic non-Heisenberg magnet with a magnetic ion spin of 3/2 on a triangular lattice are studied. It is shown that both dipole (ferro- and antiferromagnetic) and tensor (nematic and antinematic) phases can be implemented in the system. A phase diagram of the model under is constructed.

The structure, the magnetic and magnetotransport properties of perovskite Sr_0.9Y_0.1CoO_2.63 have been studied. The sample is shown to have a two-phase structure. The main phase has a tetragonally distorted unit cell and is described by space group I4/mmm. The broadening of the reflections with indices corresponding to doubling unit cell parameter c indicates the absence of the rigorous translation symmetry along axis c. The existence of the broadened superstructure reflection observed in the diffraction pattern at small angles at temperature lower than 400 K is explained by the existence of the monoclinic phase whose content is significantly lower than that of the tetragonal phase, but is dominant in the Sr_0.8Y_0.2CoO_3–δ composition. The spontaneous magnetization appears as the monoclinic phase forms. The magnetic structure is mainly G-type antiferromagnetic with magnetic moments 1.5μ_B in the layers of CoO₆ octahedra and 2μ_B in the anion-deficit CoO_{4 + γ} layers. The conduction of the Sr_0.9Y_0.1CoO_2.63 composition has a semiconducting character. The magnetoresistance is 57% in a field of 14 T at a temperature of 5 K and strongly decreases with the temperature increase.

The electrocaloric effect and also the dielectric, pyroelectric, acoustic, and piezoelectric properties of a lead magnoniobate–scandoniobate solid solution in a biasing electric field have been studied. The dielectric and electromechanical contributions to the pyroelectric and electrocaloric effects are discussed.

The energies of formation of vacancies in the carbon and silicon sublattices, the independent elastic constants, the all-round compression, shear and Young’s moduli, and the anisotropy coefficients are determined for the complete and nonstoichiometric cubic phases of 3C-Si_xC_y (x, y = 1.0–0.75) by ab initio methods of the band theory. In the formalism of the density functional perturbation theory (DFPT), the phonon dispersion dependences are obtained for these phases (the comparison with the experiment is given for the complete phase). It is shown that the mechanical characteristics of the phases become strongly anisotropic upon the transition from 3C-SiC_0.875 to 3C-SiC_0.75. It is established from the analysis of the phonon dispersion curves that the 3C-SiC_0.875 and 3C-SiC_0.75 phases, in contrast to the complete 3C-SiC phase, are dynamically unstable at T = 0 K.

The structure of the surface layer of a heterogeneous solid body (xenolite) before and after friction is studied by infrared and Raman spectroscopy. Before friction, the layer contained hornblende and pyroxene crystals. The friction resulted in partial transformation of pyroxenes into hornblende and the latter was transformed into montmorillonite clay. The xenolite surface is covered with a ~60-nm-thick layer of water.

The influence of poly- and nanocrystallinity on the parameters of pseudoelastic deformation curves of alloys with the shape memory effect (SME) has been analyzed within the theory of diffuse martensitic transformations. The functional and quantitative dependence of the coefficient of deformation (martensitic) hardening of an alloy with the SME on the grain size d and orientational factor M, dσ/dε ~ 1/Md², has been obtained for the first time, taking into account the normal distribution density of grains over their orientations and the log-normal distribution density over grain sizes d. A comparison of the found dependence with the data in the literature for a nanocrystalline TiNi alloy with nanograin sizes in the range of 8–90 nm shows good consistency between the theory and experiments.

The EPR spectrum of yttrium and scandium silicate single crystals doped with chromium has been studied at various frequencies. Y₂SiO₅ has one triclinic Cr³⁺ center, while the Sc₂SiO₅ crystals demonstrate two nonequivalent centers. The spin Hamiltonian parameters of these centers have been determined. These centers are found to be tricharged chromium ions localized in the yttrium and scandium positions.

The dependence of the conductivity of the films of hafnium oxide HfO₂ synthesized in different modes is studied. Depending on the modes of synthesis, the conductivity of HfO₂ at a fixed electric field of 1.0 MV/cm changes by four orders of magnitude. It is found that the conductivity of HfO₂ is limited by the model of phonon-assisted tunneling between the traps. The thermal and optical energies of the traps W_t = 1.25 eV and W_opt = 2.5 eV, respectively, in HfO₂ are determined. It is found that the exponentially strong scattering of the conductivity of HfO₂ is due to the change in the trap density in a range of 4 × 10¹⁹–2.5 × 10²² cm^–3. In the cathodoluminescence spectra of HfO₂, a blue band with the energy of 2.7 eV is observed which is due to the oxygen vacancies. A correlation between the trap density and intensity of cathodoluminescence, as well as between the trap density and refractive index, is found. A nondestructive in situ method for the determination of the trap density of hafnium oxide with the use of the measurement of the refractive index is proposed. The optimum values of the concentrations of oxygen vacancies for emitting devices on the basis of the films of HfO₂ are found.

Structural parameters and IR spectra of hydrates of lithium and sodium perchlorates, calcium sulfate hydrate (gypsum), and lithium nitrate hydrate are calculated ab initio using the density functional theory. The bond lengths in the water molecules are established as functions of length and energy of hydrogen bonds. The relationship between lengths of intra-anionic and hydrogen bonds is considered. The splitting of intramolecular vibrations of water is highlighted. The stretching vibration frequency of water is determined as a function of length and energy of hydrogen bonds. The combined (mixed) vibrations of anions and molecules of water with frequencies below 1400 cm^–1 are feasible as well.

A new trigonal (rhombohedral) SiC phase, existence of which was previously theoretically predicted by a symmetry analysis, is studied. It is shown that the phase can be formed during the growth of SiC films by the method of substitution of atoms on the surface of a Si substrate. Ab initio calculations of the crystal structure of a new phase and its Raman spectra are performed by the quantum chemistry method. The difference of the selection rules for the Raman active vibrations for this rhombohedral phase from the selection rules for a cubic phase in the coordinate system aligned with the translation vectors of the rhombohedral phase is established. Series of thin SiC/Si films by annealing time are synthesized by the method of the topochemical substitution of atoms, and their Raman spectra are analyzed. The presence of the spectral line (258 cm^–1), that is close to the line of a new trigonal (rhombohedral) phase calculated by the ab initio method, has been found in the Raman spectra of the samples at the initial stage of the growth of a SiC film, which indirectly confirms its existence.

The structural and magnetic properties of granular Co–In₂O₃ nanocomposite films formed by vacuum annealing of In/Co₃O₄ film bilayers at a temperature of 550°C have been investigated. The synthesized Co–In₂O₃ films contain ferromagnetic cobalt nanoclusters with an average size of 60 nm and a magnetization of ~340 emu/cm³ surrounded by the In₂O₃ layer and exhibit the thermally activated conductivity.

The theoretical studies and ab initio calculations have been carried out for the first time for atomic and electronic structure of four variants of 3C-SiC(111)-(\(2\sqrt 3 \times 2\sqrt 3 \) )-R30° surface with Si- terminated surface: initial, relaxed, reconstructed, and relaxed after reconstruction. The surface was simulated in the layered superlattice approximation by a system of thin films (slabs) with a thickness of 12 atomic layers separated by vacuum gaps of ~16 Å. In order to close the dangling carbon bonds, the opposite side of the film was complemented with 12 atoms of hydrogen. Ab initio calculations were performed by means of QUANTUM ESPRESSO program based on the density functional theory. It is shown that the reconstruction makes the atomic layers split. Our previous works and experimental data show that these splits are observed at reconstructions of surface (111) in crystals with the sphalerite structure. The band structures of four alternative slabs are calculated and analyzed. Total and layer-by-layer valence electron state densities are calculated for four top layers. It is shown that the real surface has a metallic conductivity.

Polytricyclononenes are new polymers having high permeability values not only for atmospheric gases, but also gaseous hydrocarbons. Thin films (≤100 μm) used in gas-separation membrane technologies are necessary to be studied to improve the gas transport properties of these polymers. The structure of polytricyclononene films with two vicinal side substituents Si(CH₃)₃ in a monomer unit synthesized via additive polymerization scheme is studied in this work by a small-angle neutron scattering method. As a whole, the amorphous film has a local orientation order due to chain fragments with spiral conformation. The size of the ordered regions is comparable to the length of units correlations in the polymer chain (Kuhn segment) and is 8–9 nm. Free volume and type of voids (pores) formed in the polymer film due to inhomogeneous packing are also found.

We measured Raman spectra in crystals of molecular donor–acceptor fullerene complexes {Me(nPr₂dtc)₂} · (C₆₀)₂ (Me = Ni, Cu, Pt). In the spectra of the {Pt(nPr₂dtc)₂} · (C₆₀)₂ complex under prolonged irradiation with a laser with λ = 532 nm, characteristic changes in the photopolymerization of fullerene are observed, associated with the splitting of degenerate phonon Hg modes and softening of Ag modes of the C₆₀ molecule. The kinetics of photopolymerization under conditions of weak irradiation at room temperature is studied. It was found that thermal destruction of the photopolymer with increasing temperature leads to a decrease in its concentration in the final photopolymerization product. The kinetics of thermal destruction is described by the Arrhenius equation, with the activation energy E_A of (0.68 ± 0.03) eV; the dimers are destructed to a concentration of 1% within 15 min at ~114°C.