Influence of the defect structure on the electrical conductivity of Pb5Ge3O11 single crystals at high temperatures

The impedance spectra of Pb₅Ge₃O₁₁ single crystals are measured in the frequency range from 5 Hz to 13 MHz at temperatures of 600 to 800 K in dry air and in a dry or wet nitrogen gas. It is found that the temperature and the gas composition significantly affect the electrical properties of the compound. The data obtained are used to discuss the origin of crystal lattice defects and their influence on charge transfer. It is concluded that the conduction is mixed in character (p-type electronic and ionic due to oxygen ions). The proton conduction is shown experimentally to be feasible. The possible mechanisms of proton transport in Pb₅Ge₃O₁₁ are discussed.     

Influence of concentration on the activation energy for diffusion in polymer-solvent systems

The self-diffusion of benzene, toluene, and ethylbenzene in polystyrene have been analyzed using the Vrentas/Duda free-volume diffusion model. Diffusion coefficient predictions suggest an exponential concentration dependence of the activation energy required to overcome attractive forces, E. Without the use of any diffusion data approximating E as zero over the entire concentration range yields self-diffusion coefficient predictions which are in good agreement with experimental data. © 1992 John Wiley & Sons, Inc.     

Liquid-vapor interface of square-well fluids of variable interaction range

Properties of the liquid-vapor interface of square-well fluids with ranges of interaction lambda=1.5, 2.0, and 3.0 are obtained by Monte Carlo simulations and from square-gradient theories that combine the Carnahan-Starling equation of state for hard spheres with the second and third virial coefficients. The predicted surface tensions show good agreement with the simulation results for lambda=2 and for lambda=3 in a temperature range reasonably close to the critical point, 0.8相似文献   

Cycloaddition mit ungesättigten Zuckern,VI Die Synthese Diastereomerer 4H-Pyrano [3, 4-d] Isoxazol-4-One

Abstract

By 1, 3-dipolar cycloaddition of benzonitrile oxide to 4, 6-di-O-acetyl-2, 3-dideoxy-D-erythro-hex-2-enono-1, 5-lactone (1), [3aR- (3aα, 6β,7α, 7aα)] - (2) and [3aS-(3aβ, 6β, 7α, 7aα)] -7- (acetyloxy) -6- (acetyloxymethyl) -3a, 6, 7, 7a-tetrahydro-3-phenyl-4H-pyrano [3, 4-d] isoxazole-4-one (3) were prepared in 58 and 7% yield respectively. From 2, [1′ R, 3aR-(3aα, 6β, 6aα)] -6-(1′, 2′-dihydroxymethyl)-6, 6a - dihydro-3-phenyl-furano [3, 4-d] isoxazole-4 (3aH) -one (5) was prepared by deacetylation. The structure of 3 was determined by X-ray analysis.     

Synthesis of highly substituted quinolines via heterocyclization of fluorinated acetylenephosphonates with ortho-aminoaryl ketones

A synthetic route to a series of 4-alkyl- or arylquinolines, bearing in 2- and 3-position fluorinated and phosphonate functions at the same time, is reported for the first time. These compounds are synthesized via regioselective heterocyclization of XCF₂-alkynylphosphonates (X=F, Cl, Br, H, CF₃) with ortho-aminoaryl ketones (R=CH₃, CF₃, Ph) in the presence of K₂CO₃ or Li₂CO₃/TMEDA as mediators. 2-Fluoro- and 3-phosphorus-containing 4-Me, 4-CF₃ or 4-Ph quinolines are obtained in good to excellent yields. The influence of substituents in the aromatic ketone, the XCF₂-group in the alkyne as well as mediators and the reaction medium on the reactivity and specificity of the reaction is also investigated.