Relating tracer and chemical diffusion coefficients in intermetallic compounds taking the DO3 and A15 structures

In this article we employ computer simulation to explore the validity of the Darken/Manning relation between the chemical diffusion coefficient and the tracer diffusion coefficients of the components in stoichiometric intermetallic compounds A₃B taking the DO₃ and A15 structures at vanishingly small vacancy contents. The analysis centres on the validity of Manning’s random alloy expression for the vacancy wind factor. The models for both the DO₃ and A15 structures use eight atom-vacancy exchange frequencies. For the DO₃ structure it is found that the actual vacancy wind factor is usually somewhat larger than that predicted by Manning but overall the agreement is good. At worst the use of Manning’s expression would underestimate this factor by about 30 or 40%. For the A15 structure a similar result is found except when diffusion along the chains in the structure is rapid. Then Manning’s expression fails badly when a constant geometrical tracer correlation factor is employed. In both the structures if the geometrical correlation factor is varied to reflect the structure actually explored by the atoms (mainly the majority atoms A) the agreement is improved very dramatically.     

Phase separation in La-Pr manganites and its evolution in a magnetic field

The self-consistent harmonic oscillator model including the three-dimensional cranking term is extended to describe collective excitations in the random phase approximation. It is found that quadrupole collective excitations associated with wobbling motion in rotating nuclei lead to the appearance of two-or three-dimensional rotation.     

Isotope effect for transport and magnetic properties of La 0.35 Pr 0.35 Ca 0.3 MnO 3 thin films

The effect of ¹⁶ O → ¹⁸ O isotope substitution on electrical resistivity, magnetoresistance, and ac magnetic susceptibility was studied for La_0.35Pr_0.35Ca_0.3MnO₃ epitaxial thin films deposited onto LaAlO₃ and SrTiO₃ substrates. For the films on LaAlO₃, the isotope substitution resulted in the reversible transition from a metal-like to insulating state. The applied magnetic field ( H ≥ 2 T) transformed the sample with ¹⁸O back to the metallic state. The films on SrTiO₃ remained metallic at low temperatures for both ¹⁶O and ¹⁸O, but the shift of the resistivity peak corresponding to onset of metallic state exceeded 63 K after ¹⁶ O → ¹⁸ O substitution. The temperature dependence of both resistivity and magnetic susceptibility was characterized by hysteresis, especially pronounced in the case of the films on LaAlO₃. Such a behavior gives certain indications of the phase separation characteristic of interplay between ferromagnetism and charge ordering. Received 11 February 2000 and Received in final form 13 September 2000     

Correlated tracer diffusion in an ordered interface structure

In this paper, we postulate a simple two-dimensional structure that attempts to capture the character of many of the qualitative findings from computer simulations of diffusion paths in grain boundaries. We postulate two types of mechanism: those where single atom jumps occur and those where multiple atom jumps occur. We derive analytical expressions for the tracer correlation factors, including those correlation factors that appear in the analysis of the diffusion isotope effect. We also carry out Monte Carlo simulations of these correlation factors. We find very good agreement between the derived expressions for the correlation factors and the simulation results. We are able to show that, in the absence of knowledge about the kinetic energy factor ΔK, isotope effect experiments cannot differentiate between a simple atom-jump mechanism and multiple-atom-jump mechanism.     

Reaction of Chloro(chlorodimethyl)dimethylsilane with O-Silylurethanes and Nicotinic Hydrazide in the Presence of Hexamethyldisilazane

The reaction of chloro(chlorodimethyl)dimethylsilane and hexamethyldisilazane with O-silylurethanes and nicotinic hydrazide gives rise to products whose structure is determined by the composition, structure, and basicity of intermediate compounds. The reaction allowed synthesis of previously unknown linear and heterocyclic compounds.     

Synthesis and Structure of a New Ruthenium(II) Clathrochelate and the Use of a Highly Porous Ceramic Material with an Immobilized Complex in the Oxidative Conversion of Methane

Kinetics and Catalysis - A new ruthenium(II) cage complex with polar terminal groups in the apical substituents has been synthesized; the molecular design of the complex contributes to the...     

Pattern shape control for heat treatment purification of electron-beam-induced deposition of gold from the Me2Au(acac) precursor

Gold structures can be created in a scanning electron microscope (SEM) from the Me(2)Au(acac) precursor by direct writing with the electron beam. The as-deposited purity is usually poor, and a common purification approach is a post-annealing step that indeed is effective but also induces a volume reduction because of carbon loss and an undesirable reconfiguration of the gold structure, resulting in the loss of the original shape. We studied the shape change as a result of such purification, and to minimize this effect, the application of a tantalum and chromium buffer layer was investigated. These buffer materials are well-known for their good adhesion properties. We confirm by dedicated SEM, atomic force microscopy (AFM), and transmission electron microscopy (TEM) analysis that, for the creation of a uniform Au structure, tantalum is a better buffer layer material than chromium. Post-annealing of the Au electron-beam-induced deposition (EBID) patterns for 1 h at 600 °C in air resulted in a dramatic purity increase (from 8-12 atomic % Au to above 92 atomic % Au). The uncovered part of the tantalum layer can be easily etched away, resulting in a well-defined, high-purity, gold structure.     

Tautomeric and conformational properties of benzoylacetone, CH3-C(O)-CH2-C(O)-C6H5: gas-phase electron diffraction and quantum chemical study

Tautomeric and structural properties of benzoylacetone, CH(3)-C(O)-CH(2)-C(O)-C(6)H(5), have been studied by gas-phase electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation with different basis sets up to aug-cc-pVTZ). Analysis of GED intensities resulted in the presence of 100% enol tautomer at 331(5) K. The existence of two possible enol conformers in about equal amounts is confirmed by both GED and quantum chemical results. In both conformers the enol ring possesses C(s) symmetry with a strongly asymmetric hydrogen bond. The experimental geometric parameters are reproduced very closely by the B3LYP/cc-pVTZ method.     

Phonon-mediated heat dissipation in a monatomic lattice: case study on Ni

The recently introduced analytical model for the heat current autocorrelation function of a crystal with a monatomic lattice [Evteev et al., Phil. Mag. 94 (2014) p. 731 and 94 (2014) p. 3992] is employed in conjunction with the Green–Kubo formalism to investigate in detail the results of an equilibrium molecular dynamics calculations of the temperature dependence of the lattice thermal conductivity and phonon dynamics in f.c.c. Ni. Only the contribution to the lattice thermal conductivity determined by the phonon–phonon scattering processes is considered, while the contribution due to phonon–electron scattering processes is intentionally ignored. Nonetheless, during comparison of our data with experiment an estimation of the second contribution is made. Furthermore, by comparing the results obtained for f.c.c. Ni model to those for other models of elemental crystals with the f.c.c. lattice, we give an estimation of the scaling relations of the lattice thermal conductivity with other lattice properties such as the coefficient of thermal expansion and the bulk modulus. Moreover, within the framework of linear response theory and the fluctuation-dissipation theorem, we extend our analysis in this paper into the frequency domain to predict the power spectra of equilibrium fluctuations associated with the phonon-mediated heat dissipation in a monatomic lattice. The practical importance of the analytical treatment lies in the fact that it has the potential to be used in the future to efficiently decode the generic information on the lattice thermal conductivity and phonon dynamics from a power spectrum of the acoustic excitations in a monatomic crystal measured by a spectroscopic technique in the frequency range of about 1–20 THz.     

Numerical solution of navier-stokes equations for viscous gas by the semimarching method

Translated from Chislennye Metody Resheniya Obratnykh Zadach Matematicheskoi Fiziki, pp. 225–236.