Yu. F. Kargin

Vibrational Spectra of Crystals of Bismuth Borates

The vibrational spectra of crystals of bismuth borates Bi24B2O39, Bi4B2O9, BiBO3, and Bi2B8O15 were obtained for the first time, and the spectra of Bi3B5O12 and BiB3O6 crystals measured in the range 30–1600 cm−1 at room temperature were refined. The lines observed were assigned to the corresponding vibrational transitions on the basis of the theoretical group analysis and comparison of the obtained results with the vibrational spectra of borates of different composition. The complication of the structure of bismuth borates with increasing content of B2O3 was traced by the example of vibrational spectra.

Phase relations in the Bi2O3-TiO2 system

Experimental data are presented and available published information is generalized on phase relations in the Bi2O3-TiO2 system. The phase diagrams in stable equilibrium and metastable states are constructed. The homogeneity range of the phase with a sillenite Bi12TiO20 structure is refined, and so is the temperature range of the existence of the metastable and equilibrium states of the phase with a pyrochlore Bi2Ti2O7 structure.

Optical and chiro-optical properties of crystals with sillenite structure

The experimental data on the optical and chiro-optical properties of crystals with the sillenite structure Bi12MxO20 ± δ (M= elements of II–VIII groups) have been reviewed. The relations between the changes in the chemical composition, the crystal structure of Bi12MxO20 ± δ compounds, absorption, circular dichroism, and optical rotation spectra of sillenites have been established. A model taking into account the contribution of the electronic transitions of optically active tetrahedral [MO4]n− complexes to the total optical rotation in sillenites is suggested. The data on the state (oxidation degree) and the recharging processes of 3d-elements in sillenites are systematized. The models of optical centers responsible for the photochromic effect in sillenites are critically analyzed.

Crystal-structure refinement, thermal expansion, and chemical distortion of Bi2Ga4O9

Single crystals of Bi2Ga4O9 are grown from a solution in a bismuth oxide melt. The structure (orthorhombic, space group Pbam, a = 7.918(2) Å, b = 8.299(2) Å, c = 5.894(2) Å, Z = 2) is refined to R = 0.052 in the anisotropic approximation based on single-crystal X-ray diffraction data. The structure is a framework. The bismuth(III) atoms are sixfold coordinated; gallium(III) exists in both tetrahedral and octahedral coordinations. The thermal expansion of Bi2Ga4O9 is studied by high-temperature X-ray powder diffraction method and is found to be sharply anisotropic. A structural interpretation of the anisotropy is proposed. Chemical distortion in the Bi2M4O9 compounds with M = Fe(III), Al, or Ga is analyzed and compared with the thermal expansion of Bi2Ga4O9.

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.

High-temperature heat capacity and thermodynamic properties of Tb2Sn2O7

Tb2Sn2O7 has been prepared by solid-state reaction in air at 1473 K over a period of 200 h and its isobaric heat capacity has been studied experimentally in the range 350–1073 K. The Cp(T) data for this compound have no extrema and are well represented by the classic Maier–Kelley equation. The experimental Cp(T) data have been used to evaluate the thermodynamic properties of terbium stannate (pyrochlore structure): enthalpy increment H°(T)–H°(350 K), entropy change S°(T)–S°(350 K), and reduced Gibbs energy Ф°(Т).

Properties of three-dimensional composites based on opal matrices and magnetic nanoparticles

Three-dimensional nanocomposites consisting of an opal matrix and a metal have been prepared by the interaction of salts and oxides of different elements (Ni, Co, Fe, etc.) embedded in an opal matrix with isopropanol in the range of supercritical state parameters of the alcohol. According to X-ray powder diffraction analysis and transmission electron microscopy data, the composites consist of an X-ray amorphous opal matrix with pores filled by nanoparticles of Co (or CoOx), metallic Ni, or Fe3O4 with a magnetite structure of various morphology. The sizes of the nanoparticles do not exceed the diameter of the pores in the opal matrix. A complex investigation of the nanocomposites has been performed using the electron magnetic resonance and vibrating magnetometry methods. All the studied samples at room temperature exhibit a ferromagnetic behavior. The coercive force of the samples lies in the range from 150 Oe for iron-containing nanocomposites to 565 Oe for cobalt-containing nanocomposites.

Preparation of bismuth nanoparticles in opal matrices through reduction of bismuth compounds with supercritical isopropanol

Bismuth nanoparticles have been produced in pores of opal matrices by reducing bismuth salts and oxide compounds with supercritical isopropanol. According to transmission electron microscopy data, the diameter of the SiO2 spheres in the opal matrices is about 260 nm, and that of the bismuth nanoparticles does not exceed 80 nm.

Growth and characterization of bismuth borate crystals

Optical quality single crystals and epitaxial films of Bi24B2O39 compound crystallized in sillenite-type structure have been fabricated by TSSG and liquid-phase epitaxy methods, respectively. A deviation of power rotation vs. wavelengths in visible is recorded. The important characteristics, such as: absorption, circular dichroism, photoinduced absorption, photoconductivity and dark conductivity are studied. Comparison of these characteristics is done for diAerent sillenites. ” 1999 Elsevier Science B.V. All rights reserved.

Synthesis and cathodoluminescence characteristics of europium-doped Ca-sialons

Using solid-state reactions and a combination of carbothermal reduction-nitridation with solgel processing, we have synthesized a number of oxynitride phases: Eu2+-doped Ca-sialons. We have measured the pulsed cathodoluminescence spectra of the synthesized powders under pulsed electron beam excitation and determined their emission parameters, including temporal emission characteristics.