Том 59, № 4 (2017)

A hypothesis about the existence of a pseudospinodal separating the homogeneous and heterogeneous nucleation regions in the phase diagram of a binary alloy has been proposed on the basis of the results obtained from the Monte Carlo simulation of the decomposition in a simple system with a short-range attractive potential of the impurity atoms.

Nanoisland Sn, Al, and Cu films were synthesized on dielectric substrates and their morphology and conductive properties were investigated. It is shown that the initial effective film thickness significantly affects the morphological parameters of nanoislands. Study of the surface conductivity of the films at the condensation stage revealed the conductivity drop after termination of the deposition, which is related to the nanostructuring processes. It was found that the temperature dependences of the film conductivity include three portions: the low-temperature portion of the activation growth, the decrease upon nanostructuring, and the high-temperature portion of the activation growth.

The capacitance, inductance, and dissipation factor of the Gd_xBi_1–xFeO₃ films were measured in the temperature range of 100 K < T < 800 K in magnetic fields of up to 8 kOe at frequencies of 0.1–100 kHz. The magnetic susceptibility maxima in the low-temperature region and dependences of the relaxation time and inductance on prehistory of the films cooled in zero and nonzero magnetic fields are established. The giant increase in magnetic capacitance in the external bias electric field is found. The results obtained are explained by the domain structure transformation in external electric and magnetic fields.

The physical aspects of the influence of the elastic energy anisotropy of crystals on the anisotropy of the mean free paths of phonons in single-crystal films of germanium, silicon, and diamond in the diffuse scattering of phonons at the boundaries of the samples have been considered. It has been shown that, for sufficiently wide films of germanium, silicon, and diamond with the {100} and {111} orientations and the lengths of less than or equal to their width, the phonon mean free paths are isotropic (independent of the direction of the temperature gradient in the plane of the film). The anisotropy of the phonon mean free paths depends primarily on the orientation of the film plane and is determined by the focusing and defocusing of phonon modes. For single-crystal films of germanium, silicon, and diamond with the {100} and {111} orientations and lengths much larger than their width, the phonon mean free paths are anisotropic.

The effect of partial graphitization on electrical and galvanomagnetic properties of BE-C(Fe) biomorphic carbons produced by beech wood carbonization at temperatures of 850–1600°C in the presence of an iron-containing catalyst is studied. The use of an Fe catalyst at Т_carb ≥ 1000°C leads to the formation of nanoscale graphite-phase inclusions; its total volume and nanocrystallite sizes increase with Т_carb. The data on the carrier concentration and mobility are obtained. It was shown that partially graphitized BE-C(Fe) carbons with Т_carb ≥ 1000°C in the conductivity type and magnetoresistance features relate to highly disordered metal systems whose conductivity can be described taking into account the contribution of quantum corrections, mainly the correction caused by the electron–electron interaction. It is shown that nonmonotonic dependences of the Hall constant R on the magnetic field are characteristic of BE-C(Fe) samples with 1000 ≤ Т_carb < 1600°C, which is most probably caused by the contribution of various carrier groups, i.e., electrons and holes. In BE-C(Fe) samples with Т_carb = 1600°C, the Hall coefficient corresponds to the metal state, which is associated with conducting medium homogenization resulting from the formation of a significant graphite phase volume.

Using ab initio methods, we obtained information on the crystal structure, calculated the phonon spectra, and determined the optical properties of oxyhalides Pb₃O₂Br₂ and Pb₃O₂I₂. A compound of Pb₃O₂Br₂ is synthesized, and its phonon spectra are recorded. The experimentally observed vibrational bands are assigned. A comparative analysis of the crystal lattice parameters, the phonon spectra, and the anisotropy parameters of lead oxyhalides Pb₃O₂X₂ (X = Cl, Br, I) is performed.

The problem of the energy of a spheroidal magnetic shell, solved by methods of classical electrodynamics, arises, in particular, upon the study of thin-wall biocompatible microcapsules in connection with a pressing issue of targeted drug delivery. The drug inside a microcapsule should be released from the shell at a required instant of time by destroying the capsule’s shell. The placement inside a shell of magnetic nanoparticles sensitive to an external magnetic field theoretically makes it possible to solve both problems: to transport a capsule to the required place and to destroy its shell. In particular, the shell can be destroyed under the action of internal stress when the shape of a capsule is changed. In this paper, the analysis of the model of a magnetic microcapsule in the form of a prolate spheroidal shell is performed and formulas for the magnetostatic and magnetic free energy when the magnetic field is directed along the major axis of the spheroid are derived.

The temperature dependence of the ac magnetic susceptibility of a single-crystal mixed rare-earth garnet Er₂HoAl₅O₁₂ has been investigated within the range from 1.8 to 300 K in a zero constant field and in applied bias fields of up to 9 T. In the absence of a constant magnetic field the magnetic susceptibility followed the Curie–Weiss law. The application of a constant magnetic field caused a magnetic phase transition, the temperature of which increased with increasing magnetic field. The temperature of the maximum of the ac magnetic susceptibility, which is a characteristic of the phase transition, did not show a noticeable dependence on the frequency of the alternating magnetic field.

Precise studies of the crystal and magnetic structures of M-type substituted barium hexaferrites BaFe_12–xAl_xO₁₉ (0.1 ≤ x ≤ 1.2) have been performed by powder neutron diffraction in the temperature range 300–730 K. The electric polarization and the magnetization, and also the magnetoelectric effect of the compositions under study have been studied in electric (to 110 kV/m) and magnetic (to 14 T) fields at room temperature. The spontaneous polarization and significant correlation between the dielectric and magnetic subsystems have been observed at room temperature. The magnetoelectric effect value is, on average, about 5%, and it increases slightly with the aluminum cation concentration. The precise structural studies made it possible to reveal the cause and the mechanism of formation of the spontaneous polarization in M-type substituted barium hexaferrites BaFe_12–xAl_xO₁₉ (x ≤ 1.2) with a collinear ferromagnetic structure.

The processes of molecular relaxation in the binary nitrate–perchlorate solid systems LiNO₃–LiClO₄, NaNO₃–NaClO₄, and KNO₃–KClO₄ have been investigated using Raman spectroscopy. It has been found that the relaxation time of the ν₁(A) vibration of the NO₃^- anion in the binary solid system is shorter than that in the pure metal nitrates. It has been shown that an increase in the relaxation rate is caused by the existence of an additional mechanism of relaxation of vibrationally excited states of the nitrate ion in the system. This mechanism is associated with the excitation of a vibration of another anion (ClO₄^-), as well as with the “creation” of a lattice phonon. It has been established that the condition for the realization of the relaxation mechanism is that the difference between the frequencies of the aforementioned vibrations should correspond to the range of sufficiently high densities of states of the phonon spectrum.

The vibrational spectra of uranium dioxide UO₂ and plutonium dioxide PuO₂, as well as the one-phonon densities of states and thermal occupation number weighted two-phonon densities of states, have been calculated within the framework of the phenomenological rigid ion model. It has been shown that the acoustic and optical branches of the spectra are predominantly determined by vibrations of the metal and oxygen atoms, respectively, because the atomic masses of the metal and oxygen differ from each other by an order of magnitude. On this basis, the vibrational spectra can be represented in two Brillouin zones, i.e., in the Brillouin zone of the crystal and the Brillouin zone of the oxygen sublattice. In this case, the number of optical branches decreases by a factor of two. The two-phonon densities of states consist of two broad structured peaks. The temperature dependences of the upper peak exhibit a thermal broadening of the phonon lines L01 and L02 in the upper part of the optical branches. The lower peak is responsible for the thermal broadening of the lowest two optical (T02, T01) and acoustic (LA, TA) branches.

Silicon carbide samples synthesized from silicon by topochemical substitution of atoms are studied by the ion channeling method. The results of the analysis unambiguously demonstrate the occurrence of structural heteroepitaxy. The lattice of synthesized silicon carbide of hexagonal polytype 6H is epitaxially matched in the 〈0001〉 direction with the lattice grating grid array network of an initial substrate silicon in the 〈111〉 direction. The main features of structural self-coupling matching in this epitaxial heterocomposite are revealed. Despite the very large silicon carbide and silicon lattice parameter mismatch, the misfit dislocation density at the interface is low, which is a feature of the topochemical substitution method leading to comparable structures.

The coefficient of interband absorption of a weak electromagnetic wave by quantum wires in a transverse magnetic field and an intense laser radiation field is calculated. It is shown that, if the laser radiation frequency is equal either to the size quantization frequency (dimensional infrared resonance) or to a hybrid frequency (magnetoinfrared resonance), laser illumination can determine the shape of absorption oscillations. In particular, it is shown that the second magnetoabsorption peak is split into two peaks, the half-widths of which and the distance between which depend on the intensity of resonance laser radiation. The influence of the polarization of IR radiation on the interband absorption in quantum wires is discussed. The dynamics of the frequency dependence of the optical absorption coefficient with increasing intensity of resonance laser radiation is studied.

Morphology and surface composition of the nanocomposite of thin tin layers on porous silicon, formed by magnetron sputtering, are investigated by scanning electron microscopy and X-ray photoelectron spectroscopy. It has been found that the formed nanocomposites, depending on the thickness of the deposited tin layer, differ in the ratio of main phases: tin dioxide, tin suboxide, and metal tin. The proportion of oxidized tin in the phase composition of the composites decreases from the surface to the bulk of the sample. It is found that the deposition of tin nanolayers does not cause a significant change in the phase composition of the porous silicon substrate.

The strain rate and the characteristics of the jumps at micro- and nanolevels were measured by the high-precision interferometric method for a wood-plastic composite irradiated to doses of 0–100 kGy. Radiation was shown to strengthen the material and change the characteristics of strain rate and value jumps. Strain jumps and mean-square deviations of the measured strain rate from its smoothened time dependence were determined for micro- and nanosized jumps. The change of these characteristics depending on the radiation dose of specimens was traced. A relation between the characteristics of micrometer jumps and the macroscopic strain was revealed.

Measurements of the refractive indices and optical anisotropy of a series of liquid crystalline coordination compounds based on lanthanides with an identical ligand environment have been carried out. It was found that the magnitude of the optical anisotropy of the investigated complexes was several times smaller than the anisotropy of organic liquid crystals. Analysis of the results showed that the variation of the ion complexing agent had little effect on the magnitude of the optical anisotropy in the mesogenic complexes containing the same ligands. The even-odd alternation of the optical anisotropy of lanthanidomesogens at the increasing the number of protons in the ions of the lanthanides has been observed.

Three-dimensional carbon diamond-like phases consisting of sp³-hybridized atoms, obtained by linking of carcasses of fullerene-like molecules, are studied by methods of molecular dynamics modeling. For eight cubic and one hexagonal diamond-like phases on the basis of four types of fullerene-like molecules, equilibrium configurations are found and the elastic constants are calculated. The results obtained by the method of molecular dynamics are used for analytical calculations of the elastic characteristics of the diamond- like phases with the cubic and hexagonal anisotropy. It is found that, for a certain choice of the dilatation axis, three of these phases have negative Poisson’s ratio, i.e., are partial auxetics. The variability of the engineering elasticity coefficients (Young’s modulus, Poisson’s ratio, shear modulus, and bulk modulus) is analyzed.

A new equation of state for fullerite C₆₀ is derived in the framework of the quantum-statistical method. This equation includes two Grüneisen parameters responsible for vibration–rotational and intramolecular contributions of fullerene molecules, which are represented in the form of isotropic quantum oscillators. The intramolecular vibrations of carbon atoms are described by the Debye heat capacity theory, and the cold contribution to the free energy is calculated using the Lennard–Jones pair potential for fullerene molecules. The theory is in a very good agreement with the experiment.

An increase in the thermodesorption probability under deformation wave, i.e., acoustodesorption, was estimated for alkali metal and halogen atom adsorption on single-layer graphene. To this end, first, a simple analytical expression for the adsorption energy is proposed. Second, using the previously developed adsorption M-model, the effect of the time-variable hydrostatic compression–tension of a graphene sheet on the adatom charge and adsorption energy is considered. It is shown that the derivative of the adsorption energy with respect to the strain is an order of magnitude higher for halogens than for alkali metals, and the desorbed atom flux is maximum for iodine desorption. To study the dependence of the adatom charge on the strain, the low-energy approximation (LEA) is also used. In this case, LEA estimates for alkali metals show satisfactory agreement with the results of the M-model. Within the LEA, it is demonstrated that uniaxial and hydrostatic deformations lead to order-of-magnitude identical effects.