V. M. Skorikov

Metastable states in bismuth-containing oxide systems

The temperature dependences of viscosity, density, and surface tension for Bi2O3–AO2 (A = Si, Ge, Ti) melts are found to exhibit anomalies. The temperatures of these anomalies depend on the AO2 content, which allows the liquidus fields in the phase diagrams of such systems to be divided into regions corresponding to different mesomorphic states of the melt. As shown by analyzing the processes occurring during melt heating, the mesomorphism is due to the polymerization of AO4 tetrahedra and Bi2O2 groups, which leads to an anisotropic melt structure and the development of a mesomorphic state similar to the liquid-crystalline state. For this reason, such melts retain their high-temperature structure on cooling and pass into a metastable state. Metastable phases crystallize from metastable melts. A procedure is devised for establishing the conditions of metastable equilibria by differential thermal analysis. This approach is used to carry out physicochemical analysis and construct metastable phase diagrams of the systems Bi2O3–AO with A = Mg, Ca, Sr, and Ba; Bi2O3–A2O3 with A = B, Al, and Ga; Bi2O3–AO2 with A = Si, Ge, and Ti; Bi2O3–P2O5; and Bi2O3–A2O3–P2O5 with A = B, Al, and Ga. Crystals of metastable phases are grown, and their thermal decomposition is studied isothermally and during heating. The effect of shock compression on metastable phases is investigated, and the sequence of transformations experienced by metastable phases under various external influences is analyzed. It is shown that the transition of metastable phases to the stable state is a two-step process: the first step involves precipitation of metastable binary oxides, which react in the second step to form thermodynamically stable phases. Investigation of growth defects in crystals of stable compounds demonstrates that such crystals may contain inclusions of the solidified metastable melt. The potential application fields of metastable phases are discussed.

Thermally stimulated currents in semiconductors: Analysis of rate equations for a single-level model and thermally stimulated currents in Si

Thermally stimulated currents (TSCs) in semiconductors are analyzed theoretically. The rate equations describing TSCs are solved numerically for various heating profiles, which makes it possible to evaluate the ionization energy, concentration, and capture cross section of traps. The slow and fast retrapping approximations are examined for an arbitrary heating profile. A new approach to TSC data processing is proposed: cleaning of a peak from the lower temperature peak by storing the preilluminated material in the dark at the relaxation temperature of the lower temperature peak. It is shown that heating (constant-rate or exponential) followed by isothermal holding makes it possible to determine the ionization energy of traps without knowing the retrapping mechanism. This approach is adapted for the case when the retrapping time is comparable to the carrier lifetime. Partially compensated silicon with impurity photoconductivity is prepared by doping with gold and phosphorus. It is shown that, using resonance photoexcitation, one can identify the nature (electron or hole) of traps and evaluate their ionization energy. The depths and capture cross sections of three trapping centers in Si were evaluated.

Glass formation in the Bi2O3-B2O3-BaO system

The physicochemical properties of BaO-Bi2O3-B2O3 glasses have been studied. The effect of KBF4 additions on the properties of the glasses has been examined. The transmission of the glasses has been correlated with their local structure and composition.

Efficient nonlinear optical material BiB3O6 (BIBO)

This review is devoted to a new nonlinear optical material BiB3O6 (BIBO). It systemizes data on the phase equilibrium, structure, polymorphism, and growth characteristics of single crystals of this compound and considers its main properties and fields of application. The bibliography includes 122 references.

BiFeO3 films and single crystals as a promising inorganic material for spintronics

The magnetic properties of multiferroic BiFeO3 have been considered, which are of importance for its application in spintronics.

Glass formation in the CaO-Bi2O3-B2O3 and SrO-Bi2O3-B2O3 systems

A physicochemical study of glasses based on the MO-Bi2O3-B2O3 and SrO-Bi2O3-B2O3 systems was performed. Glass formation regions were found. The structural and optical properties, as well as the thermal behavior of the glasses, were studied.

Mechanochemical activation of starting oxide mixtures for solid-state synthesis of BiFeO3

We have studied the effect of mechanochemical activation on the reactivity of Bi2O3 + Fe2O3 oxide mixtures, assessed the temperature effect on the kinetics of BiFeO3 formation in the oxide mixtures before and after mechanochemical activation, and optimized the conditions of bismuth ferrite synthesis by solid-state reaction. A material with a BiFeO3 content of at least 98.3 wt % has been obtained, and its magnetic properties have been investigated.

Phase equilibria in the BaO-Bi2O3-B2O3 system

Phase equilibria in the BaO-Bi2O3-B2O3 system have been investigated by X-ray powder diffraction analysis and DTA. Quasi-binary sections have been determined, and an isothermal section of the system in the subsolidus region has been constructed. The BaO-Bi2O3-B2O3 ternary system has been divided into 22 triangles of coexisting phases. It has been found that four bismuth barium borates exist, namely, Ba3BiB3O9, BaBi2B4O10, BaBiB11O19, and BaBiBO4. Ba3BiB3O9 undergoes a phase transition at 850°C and exists up to 885°C, where it decomposes in the solid state. BaBiB11O19 and BaBi2B4O10 melt congruently at 807 and 730°C, respectively. BaBiBO4 melts incongruently at 780°C. X-ray powder diffraction data for the low-temperature polymorph of Ba3BiB3O9 are presented.

Luminescence of europium-doped BaO-Bi2O3-B2O3 glasses

We have prepared europium-doped BaO-Bi2O3-B2O3 glasses and investigated the doping effect on the main physicochemical properties and local structure of the glasses. Using Judd-Ofelt analysis, we calculated intensity parameters (Ω2, Ω4, and Ω6), spontaneous emission probabilities, the radiative lifetime, luminescence branching factors, the quantum yield of luminescence, and the stimulated emission cross sections for 5D0 → 7FJ transitions.

Band structure of silicon carbide nanotubes

Using the linear augmented cylindrical wave method in the muffin-tin approximation, we have calculated the band structure of (n, n) and (n, 0) silicon carbide nanotubes for n = 5–10. In the range n = 7–10, (n, n) nanotubes are semiconductors, and their band gap decreases steadily with increasing n: 0.28 eV at n = 7, 0.26 eV at n = 8, 0.19 eV at n = 9, and 0.11 eV at n = 10. Nanotubes with n = 5 and 6 are metallic. At n = 7–9, (n, 0) nanotubes are semiconductors, and their band gap increases steadily with n: 0.39 eV at n = 7, 0.46 eV at n = 8, and 0.62 eV at n = 9. Nanotubes with n = 5 and 6 have metallic conductivity according to our results.