Structure and energetics of β-diketonates. IX. Molecular structure of Sr(DPM)2 according to gas phase electron diffraction data

Simultaneous electron diffraction and mass spectrometric investigation of overheated vapor of strontium dipivaloyl methanate was carned out. It was found that at 437(5)°C one molecular form, Sr(DPM)₂, prevails in the vapor. The r_a, r_g, and r_α structural parameters of the Sr(DPM)₂ monomeric molecule were determined; the molecule was found to have D_2d symmetry. The structural characteristics are compared in the series Ca(DPM)₂—Sr(DPM)₂—Ba(DPM)₂.     

Application of ion implantation for the modification of silicon-on-sapphire epitaxial systems,their structure,and properties

Articles devoted to methods for improving the structural quality of epitaxial films, which utilize the high-temperature interaction between hydrogen and silicon as well as solid-phase recrystallization process, are reviewed. A correlation between the quality of the epitaxial layer and the radiation resistance of the microcircuits obtained thereon is also considered. A method for creating capture/recombination centers in sapphire during the implantation of helium ions is proposed, yielding high-quality radiation-resistant silicon-on-sapphire films.     

Molecular dynamics study of phonon-mediated thermal transport in a Ni50Al50 melt: case analysis of the influence of the process on the kinetics of solidification

The phonon-mediated contribution to the thermal transport properties of liquid NiAl alloy is investigated in detail over a wide temperature range. The calculations are performed in the framework of equilibrium molecular dynamics making use of the Green–Kubo formalism and one of the most reliable embedded-atom method potentials for the intermetallic alloy. The phonon-mediated contribution to the thermal conductivity of the liquid alloy is calculated at equilibrium as well as for the steady state. The relative magnitude of the thermal conductivity decrease induced by the transition to the steady state is estimated to be less than 2% below 2000 K and less than 1% at 3000 and 4000 K. It is also found that the phonon-mediated contribution to the thermal conductivity of the liquid alloy can be accurately estimated (well within 1%) on the basis of an approximation which invokes the straightforwardly accessible microscopic expression for the total heat flux without demanding calculations of the partial enthalpies needed for the precise evolution of the reduced heat flux (pure heat conduction). On the basis of these calculations, the correspondence between the experimentally observed and modelled kinetics of solidification due to a difference in thermal conductivity is discussed.     

Investigation of addition mechanism of diazoles to vinylorganosilanes by methods of quantum chemistry

The behavior of pyrazole and imidazole in the reactions with vinyltrimethoxysilane and vinylsilatrane in the presence of the catalytic amount of lithium was studied by the B3LYP/6-311G(d,p) method. It is established that these processes are accompanied by the formation of lithium salts of diazoles. These substances exist in the planar and pyramidal forms in which lithium atom is bound with all atoms of the aromatic ring. Thermodynamic parameters of the process are considered, and the transition states and potential barriers are found in the approximation of isolated molecules.     

Analysis of interdiffusion via vacancy-pairs in strongly ionic solids

In this paper, we analyse chemical interdiffusion via Schottky vacancy-pairs in strongly ionic crystals for diffusion couples (AY–BY), where A and B take the same valence. We derive a sum-rule relating the phenomenological coefficients that is based on an earlier sum-rule derived by Moleko and Allnatt (Phil. Mag. A, 58 () 677) for diffusion in the multicomponent random alloy via the agency of isolated vacancies. With this sum-rule and other relationships derived by us, we show that the ratio of the intrinsic diffusivities can be expressed in exactly the same simple form as the case for diffusion via isolated vacancies. The functional form for the interdiffusion coefficient when expressed in terms of atom-vacancy exchange frequencies for diffusion is found to be essentially the same as that for isolated vacancies. The difference centres only on the relative differences of the local jump coordination of the vacancies in each case.     

Diffusion correlation effects of molybdenum and silicon in molybdenum disilicide

Diffusion data for both principal directions of silicon and molybdenum as well as germanium are briefly summarised. Analysis is performed of the defect formation energies (available from previous ab initio calculations and experimental measurements) for diffusion mechanisms via home and foreign sublattices. The home sublattice mechanism is shown to be the preferred one for both silicon and molybdenum. Tracer correlation factors for silicon and molybdenum diffusion via sublattice vacancies in the respective sublattices of the tetragonal C11_b structure of molybdenum disilicide are calculated by a direct Monte Carlo simulation technique. Correlation factors for Si diffusion on its sublattice are compared with literature values that were calculated using a more complicated Monte Carlo method based on the matrix approach. It is shown that there is no need for this complicated approach and that the direct Monte Carlo simulation technique gives highly accurate correlation factors. Correlation factors and anisotropy ratios of vacancy-mediated diffusion in both sublattices are deduced and compared with experimental data. Tracer correlation in the tetragonal direction is shown to contribute 0.40?eV (i.e. over 55%) of the migration energy of the corresponding Si diffusivity. Two possible jump rates for Si diffusion are separately estimated. Mo diffusion correlation factors are calculated using the direct Monte Carlo technique. A comparison with experiment is made and the ratio of two possible jump rates is also estimated.     

The Harrison diffusion kinetics regimes in solute grain boundary diffusion

Knowledge of the limits of the principal Harrison kinetics regimes (Types A, B and C) for grain boundary diffusion is very important for the correct analysis of depth profiles in a tracer diffusion experiment. These regimes for self‐diffusion have been extensively studied in the past by making use of the phenomenological lattice Monte Carlo (LMC) method with the result that the limits are now well established. However, the relationship of these self‐diffusion limits to the corresponding ones for solute diffusion in the presence of solute segregation to the grain boundaries remains unclear. In the present study, the influence of solute segregation on the limits was investigated with the LMC method for the well‐known parallel grain boundary slab model by showing the equivalence of two diffusion models. It is shown which diffusion parameters are useful for identifying the limits of the Harrison kinetics regimes for solute grain boundary diffusion. It is also shown how the measured segregation factor from the diffusion experiment in the Harrison Type‐B kinetics regime may differ from the global segregation factor.     

Alkynylsulfenylation of alkenes activated by phosphorus oxohalide

Russian Chemical Bulletin -     

Chemistry of Ketoacetals: II. β,β′-Ketodiacetal and β,β′-Hydroxydiacetals in Reactions with Amminia and Amines

β,β′-Ketodiacetal and β,β′-hydroxydiacetals react with ammonium acetate in acetic acid to afford substituted pyridine, and with aromatic amines in the presence of hydrochloric acid form substituted pentamethine salts.