Vol 10, No 6 (2016)

The C₆₀ and C₇₀ fullerene-cluster size distribution in aqueous solutions and a physiological medium is studied via dynamic light scattering. The initial aqueous solutions of fullerenes obtained via different methods are found to contain clusters with a characteristic size of about 100 nm. The additional aggregation of fullerenes is observed after their transfer into a physiological medium (0.9% NaCl) and is established to depend on the preparation method. The cluster-size distribution in a fullerene–pectic-acid mixture is found to vary in water and a physiological medium. The results reveal the need for additional studies of the structure and properties of C₆₀ and C₇₀ molecules, as well as their complexes with medicines, in a physiological medium for medical applications.

Anion-deficient La_0.5Ba_0.5CoO_2.8 and Y_0.25Ca_0.25Sr_0.5CoO_2.62 cobaltites are studied under pressures up to 6.5 GPa in the temperature range of 5−300 K by neutron powder diffraction. Under ambient pressure both compounds are antiferromagnetic with T_N = 250 K. The applied pressure induces in the first compound a gradual transition from the antiferromagnetic to ferromagnetic state through a mixed magnetic state, whereas the second compound remains antiferromagnetic in the whole pressure range. We suggest that the magnetic ground state depends on the unit-cell volume and the magnetic transition is associated with the transition of cobalt ions from the mixed high-spin/low-spin state to the intermediate-spin/low-spin state.

The high-resolution neutron-diffraction technique is used to determine the residual stresses and microstrains in unirradiated reactor pressure vessel surveillance specimens reconstituted by means of different welding methods. Comparative analysis of the results demonstrates that the lowest level of residual stresses is observed in the specimens reconstituted via electron-beam welding. The level of microstrains thereof is maximum, indicating a high dislocation density in the material.

The neutron structural analysis of Cu(Cr_{2 − x}Al_x)O₄ and Cu(Fe_{2 − x}Al_x)O₄ (0 ≤ x ≤ 2) nanopowders is performed. The samples are prepared by the thermal decomposition of mixed hydroxy compounds at 900°C. Different spinel phases are shown to form in Cu(Cr_{2 − x}Al_x)O₄: a tetragonally distorted phase when x ≤ 1.0, a cubic phase when x > 1.25, and a mixture of both phases when 1 < x < 1.25. As Al³⁺ ions substitute Cr³⁺ ions, a number of Cu²⁺ ions move from tetrahedral spinel sites to octahedral ones: the degree of inversion δ changes from 0 for CuCr₂O₄ to ≈0.4 for CuAl₂O₄. In the Cu(Fe_{2 − x}Al_x)O₄ system, the cubic spinel forms at all x, except x = 0. The degree of inversion δ varies from 1 for CuFe₂O₄ to ≈0.4 for CuAl₂O₄ as Al³⁺ ions substitute Fe³⁺ ions. The change in the activation energy of the water-gas shift reaction correlates with the inversion of Cu-containing spinels.

In the low-temperature (T = 4.2 K) photoluminescence spectrum of a fine-grained (the grain size is smaller than 1 μm) obliquely sputtered CdTe thin film, the dominant intrinsic emission band caused by potential barriers at grain boundaries and the edge doublet band representing the LO-phonon replica of the dominant band are observed. Doping of the film with an In impurity quenches the doublet band and subsequent heat treatment activates the intrinsic emission band. The full-width at half maximum and the short-wavelength shift of the red edge of the latter correlate with a maximum anomalously high photovoltage of 2 × 10²–10³ V generated by the film.

Carbon–cadmium alloy film coating solid solutions coexisting with amorphous carbon are for the first time obtained via ion-plasma sputtering and the codeposition of ultrafine particles of the above elements onto moving substrates. The concentration boundary of the existence of carbon solid solutions in cadmium is found to be a total carbon content in the coating of 63.5 at % (15.66 wt %). Upon the vacuum heat treatment of carbon–cadmium films with a carbon concentration of more than 57.5 at %, almost total evaporation of cadmium occurs with the formation of an amorphous carbon coating. During annealing at 1100°C, the amorphous carbon is found to crystallize into a new phase with a hexagonal primitive lattice and the parameters а = 0.6405 and с = 0.7828 nm. The face-centered cubic (fcc) phase of carbon with the lattice parameter а = 0.4265 nm is recorded in the nanocrystalline formations. The behavior of the initial film coating components during heating in vacuum is assumed, as well.

A two-stage selenization method for preparing CuInSe₂ thin films in a carrier-gas (nitrogen) flow is developed. The dependences between the morphology and structure of CuInSe₂ thin films and the selenization temperature are studied via electron microscopy and X-ray diffraction analysis. It is demonstrated that the film incorporates copper and indium selenides in the temperature range 300°C ≤ T < 400°C and a stoichiometric film with ordered chalcopyrite is formed at Т = 400°С. The possible mechanism whereby a CuInSe₂ thin film is generated with the participation of selenization centers, namely, Cu₂Se and In₂Se₃ grains, is discussed.

The transport of hydrogen isotopes in solids is an important problem for a series of applications, in particular, for future thermonuclear reactors. The main processes determining transport are the diffusion of dissolved hydrogen and its interaction with lattice defects. It is known that vacancies in a metal can capture not only one hydrogen atom, but several at the same time. General equations describing hydrogen transport in this case are presented. Special attention is focused on the influence of this effect on the thermal desorption spectra. An experimental scheme making it possible to establish the capture of several atoms to traps is proposed.

The influence of a high-power ion beam on polycrystalline oxides (V₂O₅, MoO₃, and WO₃) is investigated. Oxide irradiation with ion beams with current densities of greater than ∼30 A/cm² is established to initiate changes in the color of irradiated layers and lead to surface-layer particle melting. It is demonstrated that a distinctive feature of the interaction between a high-power ion beam and V₂O₅ is the formation of surface nanosheets and nanowires whose characteristic cross-sectional size and thickness are ∼1 μm and up to ∼40 nm, respectively. The nanosheets are generated near emerging surface cracks if the beam current density is ∼100 A/cm². Possible mechanisms of surface nanostructures formation under the action of pulsed ion beams are discussed.

A review of studies of the radiation of the excited particles ejected from metals and its chemical compounds under ion bombardment are presented. The observed features of ion-photon emission (IPE) are analyzed taking into account the physical-chemical parameters of solids and spectroscopic parameters of ejected excited particles. Different mechanisms of the ejected excited particles formation for the explanation of the experimental data are considered.

The results of collaborative research into the phase and grain-size compositions, diffuse reflection spectra, and the temperature-dependent emissivity of La_(1–x)Sr_xMnO₃ compounds synthesized as powders from La₂O₃ + SrСO₃ + MnСO₃ mixtures, performed for the first time at temperatures from–70 to +120°C, are presented. It is demonstrated that they can be used in creating smart coatings in the form of paints to stabilize the temperature of objects.

Results of experimental investigation of copper wetting by tin melts with small lead and zinc additives enriched in molybdenum, aluminum, and magnesium are presented. Microcrystalline formations are found.

The coalescence of gold and copper nanoparticles subjected to gradual heating is simulated by means of the Monte Carlo method. The interaction of nanoparticles is described using the Gupta many-body potential. It is found that the nanoparticle shape substantially affects both the melting point and the coalescence process as a whole. Moreover, there is no coalescence at all at some distances between nanoparticles in the initial configuration. The optimal parameters for creating metal nanocontacts sandwiched between nanoscale-bus tracks are determined. The obtained stable structure of nanoscale contacts is analyzed.