L. P. Efimenko

Investigation into the surface morphology of nanosized silicate and hybrid films by optical and atomic-force microscopy

This paper reports on the results of investigations into the surface morphology of hybrid organic-inorganic films prepared by the sol-gel method on single-crystal semiconductor silicon. The spin-on-glass films are coated from sols based on tetraethoxysilane. The chemical composition of the films is modified by introducing inorganic compounds (dopants), namely, boric acid and gadolinium nitrate, into the sols. For the purpose of increasing the film thickness, the sols are modified by small amounts (∼1 wt %) of polyols that have linear and branched structures, different molecular weights, and different numbers of active functional groups. A substantial change in the surface morphology of the spin-coated films, i.e., the formation of a specific structure of the films under the action of the above dopants and modifiers, is revealed using optical and atomic-force microscopy.

Synthesis of BaTiO3 powders of different dispersities by the exchange reactions in molten salts

The possibility of synthesizing BaTiO3 ferroelectric powders of different dispersities by the exchange reactions in molten salts is demonstrated. The proposed method has some advantages, such as the possibility of preparing titanate materials of different dispersities and the simplicity and controllability of the chemical process.

Thermal stability of MoSi2-SiC composites in air at temperatures of 1100–1400°C

Composites xMoSi2-(100 − x)SiC are prepared over a wide composition range (x= 10–90 mol %) by hot and cold pressing methods. The optimum pressing parameters (temperature, pressure, time) are determined. The heat resistance, the thermal stability, the porosity, and the phase composition of the composites are investigated after heat treatment for 100 h in an air atmosphere. Comparative data on the heat resistance and the porosity of the composites are analyzed as a function of the composition, the temperature (1100, 1400°C), and the preparation technique. The range of optimum compositions of the materials characterized by a low porosity and a high thermal stability is established.

Preparation of composites in the ZrB2-Si system and investigation of their properties

The refractory glass-ceramic materials based on the ZrB2-Si composite have been prepared by nonisothermal oxidation in air, and their structure, phase composition, and properties (porosity, thermal expansion, and refractoriness) have been investigated. The composite materials have a complex heterogeneous structure: crystalline particles of the initial phases (ZrB2, Si) and the phases formed as a result of oxidation in air (ZrO2, ZrSiO4, and α-cristobalite) are encapsulated in the vitreous matrix.

Kinetics of formation of ZrB2-MoSi2 glass-ceramic heat-resistant coatings on graphite

Coatings on graphite with a high heat resistance at a temperature of 1400°C in an air atmosphere are prepared on the basis of the ZrB2-MoSi2-SiO2 system. It is demonstrated that the sealing vitreous layer is formed through oxidation of the composite components. The kinetic analysis of oxidation processes of the ZrB2-MoSi2 composite shows that the coating formation results from a set of concurrent and consecutive chemical reactions. The stages of forming the gas-impermeable layer are revealed, the schemes for oxidation reactions are proposed, and the kinetic parameters of reactions are determined.

Chemical composition and crystal structure of tungsten oxide films

The most typical results of studies on the chemical and phase compositions of the tungsten oxide films synthesized by different chemical and physical methods, including the films that have undergone additional thermal treatment in vacuum and in the air, are reviewed.

Change in the optical properties of amorphous films of transition metal oxides upon formation of the nanocrystalline phase

Weakly absorbing films of tantalum oxide Ta2O5 with the crystallization kinetics typical of amorphous films have been investigated. The films have been prepared by reactive magnetron sputtering on substrates of different natures (titanium and optical silica glass). The crystallization heat treatment of the films has been performed at temperatures ranging from 500 to 700 °C. Changes in the optical properties of the films in the visible range have been studied at the initial stage of the formation of nanosized nuclei. Investigations have been carried out using X-ray powder diffraction, atomic-force microscopy, and optical measurements. It has been demonstrated that a new reflecting layer with the refractive index smaller than that of the film is formed on polycrystalline substrates due to the heterogeneous nucleation of the crystalline phase at the film-substrate interface. The crystallization of the films on amorphous substrates occurs through the homogeneous mechanism and leads to a change in the transmission coefficient of the film as a result of light scattering from the nanocrystalline phase.

Synthesis of ferroelectric powders of bismuth titanate doped with yttrium

Ferroelectric powders of bismuth titanate doped with yttrium ((Bi0.8Y0.2)4Ti3O12) have been fabricated using the method of synthesis in multicomponent melts. It has been established that doping with yttrium (in contrast to lanthanum) results in the decrease of the material’s Curie temperature and dielectric permittivity.

Thermal stability of MoSi2-TiB2-CrB2 composites at 900–1400°C

Slip casting procedure with subsequent firing in air is used to synthesize composites (100 − x)MoSi2−xMB2, where M = Ti, Cr, (Ti, Cr) and x = 10, 20, and 30 mol % at 900–1400°C. The MoSi2-CrB2 and MoSi2-(Ti, Cr)B2 composites containing 20 and 30 mol % of borides are found to possess the highest protective properties. The optimum temperature range for sintering is 1100–1400°C.

Investigation of the morphology of films based on sodium silicate by atomic-force microscopy

The characteristic features of the surface morphology of the films prepared by alkaline hydrolysis of silica are investigated using atomic-force microscopy. It is shown that the surface morphology of the films is influenced by the concentration of initial solutions and the modes of dehydration that are responsible for the processes of aggregation of nanoparticles, which affects the ratio between the amorphous and crystalline phases on the surface of the coating