Vol 59, No 6 (2017)

A consistent procedure for determining the ionization potential of a large metal cluster of radius R_{N, v}, consisting of N atoms and N_v vacancies, is proposed. The perturbation theory in small parameters R_v/R_{N, v} and L_v/R_v (Rv and L_v are average distance between vacancies and the length of electron scattering on vacancies, respectively) is constructed in the effective-medium approximation for the electron ground state energy. The effective vacancy potential profile, the electron scattering phase and length are calculated by the Kohn–Sham method for a macroscopic metal in the stable jelly model. The obtained analytical dependences can be useful to analyze the results of photoionization experiments and to determine the size dependence of the vacancy concentration, including that near the melting temperature.

The ac conductivity of Bi₁₂TiO₂₀: Ru crystals has been studied in the frequency range 10²–10⁶ Hz and at temperatures 293–773 K. The experimental data have been analyzed in the framework of the model of correlated barrier hops. In this material, the potential barriers are due to the existence of a block structure, crystal lattice defects, and also the presence of a ruthenium impurity. The microparameters characterizing the charge transfer in doped bismuth titanate single crystals have been determined.

The state equations and the pressure dependences of the lattice properties have been obtained for various polymorphous modifications of silicon and germanium using the Mie–Lennard-Jones pair interatomic potential and the Einstein crystal model. It is shown that the elastic-type interatomic potential gives the best results for the semiconductor phase and the plastic-type interatomic potential for the metalized phases whose potential well depth is significantly smaller. The pressure dependences of the lattice properties are calculated along isotherm 300 K and the jumps of the properties during the phase transition from the diamond structure to the β-Sn phase are evaluated for both silicon and germanium. The calculated results agree well with the experimental data.

The replica Monte Carlo method has been used to investigate the critical behavior of a threedimensional antiferromagnetic Ising model on a body-centered cubic lattice, taking into account interactions of the adjacent behind neighbors. Investigations are carried out for the ratios of the values of exchange interactions behind the nearest and next nearest neighbors k = J₂/J₁ in the range of k ∈ [0.0, 1.0] with the step Δk = 0.1. In the framework of the theory of finite-dimensional scaling the static critical indices of heat capacity α, susceptibility γ, of the order parameter β, correlation radius ν, and also the Fisher index η are calculated. It is shown that the universality class of the critical behavior of this model is kept in the interval of k ∈ [0.0, 0.6]. It is established that a nonuniversal critical behavior is observed in the range k ∈ [0.8, 1.0].

The direct and indirect measurements of intensive electrocaloric effect in a triglycine sulfate ferroelectric crystal are performed under equilibrium and nonequilibrium thermodynamic conditions implemented in the adiabatic calorimeter. The effect of the electric field parameters (frequency, profile, and strength) on the value of the effect and degree of its reversibility are studied. The difference between the temperature variation values in a switched-on and switched-off dc field under quasi-isothermal conditions is established. The low-frequency periodic electric field induces the temperature gradient along the electrocaloric element and heat flux from its free end to the thermostated base. A significant excess of the field switching-off rate over the switching-on rate leads to a noticeable intensification of the cooling effect.

A continuous stiffness measurement method allowing one to obtain physical-mechamical characteristics of materials in the process of indentation during gradually increasing loading has been scrutinized. The limits of applicability of this approach depend on the testing conditions at which the additional smallamplitude oscillations exert no influence on the mechanics, kinetics, and plastic strain of material being in contact with the indenter. As is shown by taking as examples specimens with amorphous structure, and fcc and bcc lattices, various techniques for determining the nanocontact characteristics of materials are different by their sensitivity to small-amplitude load oscillations. The oscillation amplitudes and the indentation depth ranges where one can neglect the oscillation effects have been evaluated. The impacts of the oscillations on the behavior of the contact (local) characteristics of the studied materials in supercritical modes have been established.

The effect of impurities on the efficiency of the formation of color centers and hydrogen-bonded molecular complexes upon exposure to various radiations in lithium fluoride crystals grown in air is studied. The results of experiments for measuring optical properties, IR vibrational spectra, luminescence, and thermally stimulated luminescence are presented. The fact that the band in the range of 1800–2300 cm^–1 corresponds to stretching vibrations of a complex with strong hydrogen bond is proved based on the Fermi-resonance perturbation in the region of 2080 cm^–1, shaped as the Evans hole and bands A, B, and C. It is shown that the composition of these complexes includes an OH^– ion and an HF molecule. The crucial role of O^2‒V_a⁺ oxygen dipoles in the aggregation efficiency and gradient distribution of color centers and radiation resistance of hydroxyl ions is revealed. It is shown that products of radiation decomposition of OH^– ions stimulate, while decay of O^2‒V_a⁺ dipoles suppress, the formation of positively charged color centers.

Magnetooptical investigation of exciton transitions in high-quality quantum wells of an (In, Ga)As/GaAs heterosystem has been carried out. Investigation of transmission of free-hanging samples detached from the substrate in the magnetic fields of up to 12 T revealed a rich fine structure associated with various heavy-hole and light-hole exciton transitions. In particular, transitions from the excited states of light holes localized in a Coulomb potential produced by an electron along the heterojunction axis (a Coulomb well) have been detected. Taking into account consistently stresses, formation of Landau levels, the binding energies of excitons (diamagnetic excitons), and the effect of a Coulomb well, we have succeeded to describe the experimental results with the use of a self-consistent variational procedure. As a result, new features in the structure of optical transitions have been explained and the effective masses of electrons and holes of excitons formed by both heavy and light holes have been determined with a high accuracy.

The influence of pressure and temperature on low-frequency lines (100–300 cm^–1) in Raman spectra of ZrB₁₂ and LuB₁₂ single crystals has been investigated. These spectral features have been identified as one-phonon and two-phonon excitations of the acoustic branches of the phonon spectrum. It has been found that the observed spectra of ZrB₁₂ single crystals are more structured and indicate the development of phonon anomalies with a decrease in the temperature. Despite the fact that the low-frequency features in the phonon spectrum of ZrB₁₂ are characterized by a high value of the isothermal Grüneisen parameter, their isobaric Grüneisen parameter has a negative value. This indicates large contributions from the fourth-order anharmonicity, which significantly exceed the volume effects. The appearance of narrow lines in the frequency range from 155 to 175 cm^–1 at temperatures T < 100 K suggests the possibility of a structural transition with an incomplete softening of the lattice.

A new class of defect structures in which point defects of a crystal lattice simultaneously occupy sites of two different superstructures is proposed. The formation of these structural modifications is due to a second-order order–order phase transition that does not occur to the end. The allowable relation between the long-range order parameters in the structural modification formed by a combination of the monoclinic (M₅X₅)_mon (space group C2/m (A2/m)) and the cubic (M₅X₅)_cub (space group Pm3m) of the superstructures is studied using an atom–vacancy ordering in titanium monoxide TiO_1.0. The thermodynamic calculations show that the proposed structural modification is equilibrium and must form instead of assumed high-temperature cubic phase (Ti₅O₅)_cub.

The chemical and the phase compositions of multilayer nanoperiodic SiO_x/ZrO₂ structures prepared by vacuum evaporation from separated sources and subjected to high-temperature annealing have been studied by X-ray photoelectron spectroscopy with a layer-by-layer etching. It is found that, under deposition conditions used, the silicon suboxide layers had the stoichiometric coefficient x ~1.8 and the zirconium-containing layers were the stoichiometric zirconium dioxide. It was found, using X-ray photoelectron spectroscopy, that annealing of the multilayer structures at 1000°C leads to mutual diffusion of the components and chemical interaction between ZrO₂ and SiO_x with predominant formation of zirconium silicate at heteroboundaries of the structures. The SiO_x layers of the annealed nanostructures contained ~5 at % elemental silicon as a result of the phase separation and the formation of fine silicon nanocrystals.

An electron microscopic investigation was performed on the kinetics of the layer and island crystallization of amorphous V₂O₃ films deposited by pulsed laser evaporation of vanadium in an oxygen atmosphere. The crystallization was initiated by the action of an electron beam on an amorphous film in the column of a transmission electron microscope. The kinetic curves were plotted on the basis of a frame-by-frame analysis of the video recorded during the crystallization of the film. It was found that the layer crystallization of amorphous films is characterized by a quadratic dependence of the fraction of the crystalline phase x on the time t, whereas the island crystallization is described by an exponential dependence of x on t. The kinetic curves of island crystallization of amorphous films were analyzed on the basis of the α-version of the Kolmogorov model. For each type of crystallization, there are specific values of the dimensionless relative length unit δ₀, which is equal to the ratio of the characteristic length unit to the parameter characterizing the unit cell of the crystal. It was established that, for the layer crystallization, the relative length unit lies in the range δ₀ ~ 4300–4700, whereas for the fine-grained island crystallization, it amounts to δ₀ ~ 110.

The interaction between a silicon vacancy and a carbon atom formed in silicon during the topochemical synthesis of silicon carbide from silicon has been calculated using the density functional theory method. It has been shown that the silicon vacancy and the carbon atom are attracted to each other, and the strongest attraction is observed in the 〈111〉 direction. It has been established that there a qualitative agreement between the quantum-mechanical theory and the theory based on the Green’s function method for point defects. It has been concluded that the silicon vacancy and the carbon atom form a bound state in silicon. The effective stiffness coefficient of this coupling in the 〈111〉 direction has been estimated to be 5 eV/Ų.

Soluble electron-donor conducting (co)polymers based on functionalized monomeric anilines have been synthesized and characterized for the first time. It has been shown that there is a good correlation between the results obtained from investigations of the electrochemical properties of polyaniline derivatives by the methods of cyclic voltammetry and on the basis of the temperature dependence of the electrical conductance. The polymer based on 2-(1-methyl-2-buten-1-yl)aniline has the lowest energy level of the highest occupied molecular orbital, which determines the prospects for its use as a donor in the active layer when designing organic solar cells.

A molecular mechanical model has been proposed for nanoribbons of graphone (graphene with single-sided hydrogenation), which takes into account deformations of valence bonds, valence and torsion angles, as well as non-bonded van der Waals and Coulomb interactions of atoms in a graphone nanoribbon. The ground states of the nanoribbons have been found using the proposed model. It has been shown that a rectangular fragment of graphone on a substrate formed by an infinite planar graphene sheet forms a flat monolayer, whereas a fragment that does not interact with the substrate takes a convex shape, the outer side of which contains the attached hydrogen atoms. The simulation of the dynamics has demonstrated that the single-sided structure of a graphone sheet is resistant to thermal vibrations (at temperatures T < 900 K, hydrogen atoms do not migrate from one side of the sheet to the other). The difference between the sides leads to a rapid folding of long-length free-standing graphone nanoribbons into scrolled structures. Thermal vibrations do not prevent the formation of scrolls, and the scrolls themselves are resistant to these vibrations.

CuV₂O₆ and Cu₂V₂O₇ compounds have been produced from initial components CuO and V₂O₅ by solid-phase synthesis. The high-temperature heat capacity of the oxide compounds has been measured using differential scanning calorimetry. The thermodynamic properties (the enthalpy change, the entropy change, and the reduced Gibbs energy) have been calculated using experimental dependences C_P = f(T). It is found that there is a correlation between the specific heat capacity and the composition of oxides of the CuO–V₂O₅ system.