Selective laser spectroscopy of Mn4+-Mn4+ pair centers in SrTiO3 crystal

Zero-phonon lines of a pair center of Mn⁴⁺ ions are observed in the luminescence and luminescence-excitation spectra of SrTiO₃:Mn crystal. Based on the experimental data, the energy-level structure of the ground state ∣⁴ A _2g ,⁴ A _2g 〉 and excited state ∣⁴ A _2g ,² E _g 〉 of the Mn⁴⁺-Mn⁴⁺ pair center is constructed. It is shown that the exchange interaction in the ground state of the Mn⁴⁺-Mn⁴⁺ pair is antiferromagnetic. Energies of the levels are calculated assuming that the pair is formed by Mn⁴⁺ ions occupying neighboring octahedral positions of Ti⁴⁺ ions along the [110] axis. Experimental values of the exchange integral in the ground state ∣⁴ A _2g ,⁴ A _2g 〉 and energies of spin multiplets in the excited state ∣⁴ A _2g ,² E _g 〉 agree well with calculation of the exchange interaction carried out within the framework of the channel model with the parameters J _ξη = 32 cm^4-1 and J _ζζ = ?45.5 cm^4-1. Experimental data and calculations unambiguously demonstrate that zero-phonon lines in the luminescence and luminescence-excitation spectra have magnetic-dipole nature.     

Microscopic structures of the B7 phase: AFM and electron microscopy studies

A wide variety of morphologies, such as screw-like filaments, ribbons, etc., have been observed in polarizing microscopy studies of the B₇ phase in a melt or with free surface. In this paper, we present the results of AFM and scanning electron microscopy measurements of structures formed by a columnar-type B₇ phase. These measurements are aimed at elucidating the three-dimensional structure of the observed patterns.     

Relationship between strict and approximate models in the problem of transformation of evanescent waves

The transformation of evanescent waves near a layered substrate is considered. A comparative analysis of results obtained on the basis of rigorous and approximate approaches is performed. It is shown that the use of approximate models may lead to erroneous results.     

Incomplete block factorization methods for complex-structure matrices

Two classes of SSOR-type incomplete block factorization methods are proposed for preconditioning of linear algebraic systems of equations with block banded matrices of complex structure. Correctness conditions are derived for these methods in application to M-matrices and their efficiency is demonstrated by numerical experiments with linear algebraic systems obtained by discretization of the three-dimensional Poisson equation using quadratic and cubic serendipity finite elements. Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 159, pp. 5–22, 1987.     

Chiral ordering in the nematic and an optically isotropic mesophase of bent-core mesogens with a halogen substituent at the central core

Two new homologous series of bent-core compounds have been synthesized. Their mesophase behaviour has been investigated by polarizing microscopy, differential scanning calorimetry, X-ray diffraction, NMR spectroscopy, and by dielectric and electro-optical measurements. It was found that, with one exception, all the chlorine-substituted compounds form a nematic phase and an optically isotropic 'banana phase'. The latter phase shows spontaneously chiral domains of opposite handedness. This phase may be considered as a type of smectic blue phase. The mesophase behaviour of the homologous bromine-substituted compounds is more complicated. Depending on the chain length, B₆, columnar, nematic or the isotropic 'banana phase' occur.     

Preparative Procedure for the Reduction of Substituted Nitroarenes with Hydrazine Hydrate in the Presence of a Nickel–Cobalt Nanocatalyst

A preparative procedure has been proposed for the reduction of substituted nitroarenes with hydrazine hydrate in the presence of a nanocatalyst based on cobalt–nickel nanoparticles, which ensured selective formation of the corresponding anilines in 78–80% yield in 20–45 min.     

Binuclear Ruthenium(III) μ-Oxocarboxylates of the Nonelectrolyte Type. Molecular Structure of the Complex [Ru

Binuclear ruthenium μ-oxocarboxylates of the nonelectrolyte type [Ru ₂ ^III (μ-O)(μ-O₂CR)₂Py₄(O₂CR)₂] (R = C(CH₃)₃, CH₃, Ph, CH₂Cl, CCl₃, and CF₃) were obtained and studied by electronic absorption and IR spectroscopy and FAB mass spectrometry. The carboxylate ions RCO ₂ ⁻ are symmetrically arranged (trans with respect to the bridging μ-O atom) and coordinated in a monodentate fashion. According to X-ray diffraction data, the crystals of [Ru ₂ ^III (μ-O)(μ-O₂CCF₃)₂Py₄(O₂CCF₃)₂] ⋅ (CH₃)₂CO are monoclinic; the unit cell parameters are a = 11.705(2) Å, b = 16.166(3) Å, c = 20.917(4) Å, β = 103.47(3)°, space group C2/c, Z = 4. The RCO ₂ ⁻ groups that are trans to the μ-O atom can be easily replaced by pyridine or acetonitrile. __________ Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 11, 2005, pp. 803–809. Original Russian Text Copyright ? 2005 by Eremin, Belyaev, Simanova.