Publications

Preparation of modified ruthenium molecular sieves has been investigated in two steps deposition of ruthenium and modifying of ruthenium molecular sieves in presence of ligands. As support sieve there were used two molecular sieves with large pore apertures and low acidity strength (zeolite L and APO-34). Correlation of in situ W-VIS ruthenium deposition measurements with catalyst characterisation revealed that ruthenium deposition takes place not only through ionic exchange but also through adsorption of ruthenium hydrolysed species. Modifying of the ruthenium molecular sieves catalysts with ligands has as effect a diminution of electronic charge on metal. The experimental data indicate that the presence of ligand favours an enantioselective hydrogenation of D-fructose to D-mannitol even if the yields are not very high.

A sequential algorithm, leading to three-dimensional polytetrahedral dense random packing structures is employed to simulate the atom-by-atom growth of relatively small clusters, under a large variety of physical assumptions. The computer model developed can provide information about the influence of experimental growth conditions on the topological and energetical parameters of the cluster : average coordination number, atomic pair distribution function, the degree of local tetrahedral perfection and specific bonding energy as a function of cluster size. The degree of icosahedral order built-in during the simulated growth process can be estimated from the pair distribution function and is of particular interest, due to its relevance to quasicrystalline thin films investigation.

Films of C-60, at different stages of annealing of T-c = 200 degrees and 300 degrees C have been electrical characterized over the temperature domain from -130 degrees C to T-c. X-ray diffraction revealed a random polycrystalline fee structure with stacking defects of an intrinsic nature, due to deposition conditions. The value of room-temperature conductivity was found to be in the range (6.3-1.0)*10(-10) (Omega cm)(-1). In the stable annealed state the conductivity showed an activated temperature dependence above 423 K and a non-activated dependence below 330-280 K. The activation energies E(2) 0.8 eV (film thickness 0.70 mu m) and E(2) = 1.0 eV (film thickness 2.40 mu m) were in good agreement with the energy gap values (1.63 eV and 2.08 eV) which were deduced from the al;sorption spectral dependence. Annealing decreased the non-activated contribution to conduction, extending the intrinsic conduction temperature range.

We report on the first simultaneaous investigation of the behavior of ligand field and charge transfer bands in doped Bi12GeO20 (BGO) under various illumination and thermal conditions. This was made possible through MCD measurements in both the near IR and the visible spectral regions. The [MnO4](3-) ion is clearly identified in the thermally bleached state. Illumination with blue light leads to the reduction of Mn5+ while the antisite (Bi-Ge(3+) + h) defect is formed. Finally EGO is an interesting host for the popular d(2) ions in a tetrahedral site.

High T-c bulk superconductors Y(Tm)Ba2Cu3O7-x and YSryBa2-yCu3O7-x were pre pared following new synthesis routes by the method of thermal decomposition of polynuclear coordination complexes. The best superconducting samples were obtained using oxalic and malic acids as ligands. The effect of substituting of Pa by Sr nas a decrease of T-c with increasing the Sr:Ba ratio. Electrical resistance, magnetic susceptibility and structural measurements have been performed on the superconducting samples.