State of iron atoms in SiO2·xFe2O3 gels

Mössbauer studies are made of ⁵⁷Fe nuclei in dry SiO₂·xFe₂O₃ gels at low temperatures in external magnetic fields. It is shown that the state of the iron atoms in the gels depends significantly on their concentration. In dry gels with an iron content exceeding 0.01Fe₂O₃, the Fe atoms belong to finely dispersed particles of the oxide with maximum sizes of ～80 Å in a superparamagnetic state. For lower iron contents, the Fe atoms are in the form of a highly diluted paramagnetic impurity of trivalent ions in a diamagnetic matrix. It is assumed that clusters develop from a small number of iron and oxygen ions dispersed in the gel matrix. Here spin-lattice relaxation of the magnetic moments of the iron atoms is observed.     

Synthesis and conversions of metallocycles. 22. NMR studies of the mechanism of Cp2ZrCl2-catalyzed cycloalumination of olefins with triethylaluminum to form aluminacyclopentanes

The mechanism of cycloalumination of olefins under the action of AlEt₃ in the presence of Cp₂ZrCl₂ giving rise to aluminacyclopentanes was investigated by dynamic ¹H and ¹³C NMR spectroscopy. The bimetallic complex Cp₂ZrEtCl–AlEt₃ is formed initially and is converted into the bridged complex Cp₂Zr(Cl)CH₂CH₂AlEt₂ as a result of beta-hydride shift and elimination of the ethane molecule. The resulting complex adds a molecule of the initial olefin yielding aluminacyclopentanes. Under the action of Et₂AlCl in the presence of an excess of AlEt₃, zirconacyclopentanes give rise to intermediate bimetallic complexes stable at -70 °C. Under the reaction conditions, the latter compounds are converted into aluminacyclopentanes.     

Requirements to the accuracy of the Burnett transport coefficients

Some effects in gases are completely or partially determined by the Burnett terms of the stress tensor and the heat flux vector. Usually, approximate values of the Burnett transport coefficients for a monatomic gas are used to calculate the above-mentioned quantities. “Exact” expressions for these coefficients correct to values less than one percent are obtained for elastic-sphere molecules. The results of calculations of certain such effects are compared with one another using the approximate and exact Burnett transport coefficients for a monatomic gas consisting of elastic-sphere molecules.     

Probe Mössbauer Diagnostics of Charge Ordering in Manganites CaCuxMn7–xO12 (0 ≤ x ≤ 1)

Journal of Experimental and Theoretical Physics - We present the results of our 57Fe probe Mössbauer study in manganites CaCuxMn6.96–x57Fe0.04O12 (0 ≤ x ≤ 1). We have...     

Mössbauer and Magnetic Study of Lanthanum Manganite La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20): Nonstoichiometric and Stoichiometric Composition

Crystallography Reports - Mössbauer and magnetic study of calcium-doped lanthanum manganites La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20)...     

Comparison of Transmission Electron Microscopy and X-Ray Reflectometry Data in the Study of the Structure of Silicon-Carbon Nanocomposite Films

Crystallography Reports - Vanadium-doped diamond-like silicon-carbon films have been studied by X-ray reflectometry and transmission electron microscopy. A comparison of the data obtained has shown...     

Changes in the Magnetic Structure of Multiferroic BiFe0.80Cr0.20O3 with Temperature

Physics of the Solid State - The results of a Mössbauer study of the magnetic structure of multiferroic BiFe0.80Cr0.20O3 in the temperature range of 5–550 K are presented. It is found...     

Physical Methods for Determining the Phase Composition of Gallstones

Crystallography Reports - Gallstones with a zonal morphological structure have been studied using X-ray microtomography, X-ray diffraction analysis, Raman spectroscopy, and elemental analysis....     

Structure of the local environment and hyperfine interactions of <Superscript>57</Superscript>Fe probe atoms in DyNiO<Subscript>3</Subscript> nickelate

The local structure of DyNiO₃ nickelate at both sides of the insulator (T < T _im) ? metal (T > T _im) phase transition was studied by probe ⁵⁷Fe Mössbauer spectroscopy. The character of change in the hyperfine parameters of probe iron atoms specifically near the phase-transition temperature (T ≈ T _im) was analyzed.