Nature of the surface layer in ABO3-type perovskites at elevated temperatures

X-ray diffraction measurements showed that in the surface layer of perovskite structure BaTiO₃, SrTiO₃, PbTiO₃ and KNbO₃ crystals at elevated temperatures (500–1000°C) reactions take place in the solid phase, associated with segregation in the direction to the surface of AO complexes, leading to the formation of a whole homologue series of crystalline compounds with the general formula AO · (ABO₃) _n ,n = l, 2,....., 10, Lowered oxygen partial pressure may inhibit the segregation processes and in the range of temperatures for which vaporisation of the AO complexes from the surface does not yet take place a suitable choice of oxygen pressure may lead to resynthesis of the compound.     

The electronic structure of ordered Cu3Au(001)

The electronic structure of the (001) face of ordered Cu₃Au was studied using synchrotron radiation at BESSY, in the photon energy range 22–80 eV. The Cu 3d-derived bands in Cu₃Au look like the foldedd-bands of fcc Cu metal. Three Au 5d-derived bands were observed at 5.0, 6.1 and 7.0 eV below the Fermi level, which showed no dispersion with change in photon energy. The Cu 3d- and the Au 5d-derived bands are found to be separated in energy. We have calculated self-consistent energy bands along the (001) direction using the fully relativistic LMTO method. Comparison of these bands with those experimentally determined shows good agreement. From the calculated bands along –X the direction dependent densities of states were determined, which give a consistent account for the non-dispersive Au-bands.     

Supported metals and metal oxides as promoters for the metal dimer and cluster catalysed co substitution reaction

Promotional effects due to PtO₂, PdO, Pd/C and Pd/CaCO₃ on the metal dimer or cluster (e.g. [(η⁵-C₅H₅)Fe(CO)₂]₂, Ru₃(CO)₁₂, Ir₄(CO)₁₂) catalysed reaction between metal carbonyls and isonitriles are shown to lead to enhanced reaction rates for the metal carbonyl substitution reaction.     

Identification of surface states on finely divided supported palladium catalysts by means of inelastic incoherent neutron scattering

The purpose of the present investigation was to utilize the inelastic incoherent neutron scattering (INS) technique to reveal changes at the surface of technical catalysts under the influence of hydrogen in gas/solid interactions and during chemical reactions in a liquid-phase process. The formation and the properties of supported palladium hydride and changes of the hydrogen-related surface chemistry of the corresponding activated carbon supports in 20% Pd/C catalysts after short-term and long-term hydrogen cycling at different hydrogen pressures and temperatures were studied. The spectra indicate that hydrogenation of the activated carbon support by hydrogen spillover occurs to, partly, give a material that strongly resembles a-C:H (amorphous hydrogenated carbon). Indications for different relaxation phenomena and long-range phase coherence inside of supported particles of palladium hydride compared to hydrogenated palladium black were obtained. A 5% Pd/C catalyst after use in C-C coupling reactions, the Heck reaction of bromobenzene and styrene to stilbenes, was also studied after subsequent solvent extraction. Evidence for a preferential adsorption and accumulation of cis-stilbene at the catalyst surface was obtained. INS allows identification of a certain isomer from a complex reaction mixture preferentially adsorbed at the surface of a finely divided industrial heterogeneous catalyst.     

Dimeric ruthenium(II) complexes containing bridging carboxylato and aquo ligands. The crystal structure of μ-aquobis(μ-trifluoroacetato)bis[(η4-cycloocta-1,5-diene)(trifluoroacetato)ruthenium(II)]

Protonation of [Ru(μ³-C₃H₄R)₂(C₈H₁₂)] (R = H, Me; C₈H₁₂ = cycloocta-1,5-diene) with haloacetic acids gives the dimers [Ru₂(C₈H₁₂)₂(O₂CR′)₂(μ-O₂CR′)₂-(μ-OH₂)] (R′ = CF₃, CCl₃ and CH₂Cl), which are precursors for a range of monomeric and dimeric ruthenium carboxylate complexes. The complex [Ru₂(C₈H₁₂)₂-(O₂CCF₃)₂(μ-O₂CCF₃)₂(μ-OH₂)] has been characterized by X-ray analysis.     

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