Abstract: Superconducting Cu mixed oxyfluoride, Sr,Cu(O, F)(4+delta), was Obtained via fluorination of Sr2CuO3 by XeF2 in the 100-250 degrees C temperature range in a closed Ni container. The prepared samples exhibited a lower T-c in comparison with earlier reported values. Different samples in the Sr-Cu-O-F system were prepared by a solid-state reaction at 220-400 degrees C, but no formation of the oxyfluoride was detected even with an addition of xenon difluoride. These data allow one to draw conclusions on the metastability of the oxyfluoride under the conditions used, Electron microscopy and X-ray powder diffraction studies revealed large amounts of badly crystallized SrF2; this could be a reason for the small superconducting volume fraction as well as for the inhomogeneous distribution of the anions.

Abstract: A hot dip aluminizing process to simulate the continuous galvanizing line (CGL) was carried out in three successive steps by a hot dip simulator: the pre-treatment for removing scales on the 200 x 250 mm(2) and 1mm in thickness cold rolled steel sheet, the dipping in 660 degrees C Al-Si melt for 3s and the cooling. In a pre-treatment, the steel specimen was partly coated by Au to confirm the mechanism of intermetallic compound (IMC) formation. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) analyses were followed to observe the cross-section and the distribution of the elements. The specimen was analyzed in the boundary of the dipped-undipped part to see the formation mechanism of the aluminized steel. An intermetallic compound (IMC) is rapidly developed and grown in the steel-liquid interface. It has been usually reported that the IMC was formed by the dissolution of iron in the steel substrate toward the melt and the diffusion of aluminum in an opposite direction. The specimen is covered with aluminum-10 wt.% silicon, forms the IMC in the part that was not Au coated. However, IMC is not formed in the Au-coated part. The interface of the dipped-undipped is also analyzed by EDX. At the interface of the steel-IMC, it is clearly shown that the IMC is only formed in the dipped part and exists in the steel substrate as well, and contributes by iron, aluminum and silicon. The result clearly shows that only aluminum diffuses into the steel substrate without the dissolution of iron and forms the IMC between the steel substrate and the melt. Au coating and the short dipping time prevent the iron from dissolving into the aluminum melt. By TEM combined with focused ion beam (FIB) sample preparation, the IMC is confirmed as Fe2SiAl8, a hexagonal structure with space group P6(3)/mmc.

Abstract: The influence of the amount of catalyst and the reaction time on the quantity and quality of catalytically grown single wall carbon nanotubes (SWNT) was investigated. The aim was to optimize some of the SWNT growth parameters using TEM and HRTEM. The thickness of catalyst layer influences the synthesis of the nanotube because the gas composition can differ between top and bottom. Microscopic investigation of the grown SWNT samples showed that the thicker the catalyst layer the lower relative nanotube content, so the deeper parts of the catalyst layer are less effective: The optimum time for the reaction was found to be 10 minutes. This may be understood assuming that nanotube growth needs an initial incubation time while the activity of the catalyst decreases steadily until the nariotube growth stops.

Abstract: A model for superstructure ordering in the <<chain>> layers of Ga (Co) substituted YBCO intergrowths with general formula (REO2)NSr2MCu2O5 (M = Co, Ga; n = 1, 2, ...) is proposed. By Ga or Co substitution for Cu, the structure of the <<chain>> layer changes : instead of the CuO4 planar squares, the chains consist of MO4 tetrahedra (M = Ga, Co) running along the [110] perovskite direction. The existing model for the Ga substituted <<123>> implies that all the chains are the same. Our new model is based on the results of Electron diffraction and High-resolution electron microscopy investigations. The model reveals the occurrence of two types of chains as a consequence of <<opposite>> ordering between neighbouring tetrahedra. The comer linked tetrahedra in each chain appear as alternatingly rotated in opposite sense, and a chain itself, as being displaced with respect to the underlying structure in one of two senses ; either forth (right) or back (left) along the chain direction. The regular alternation of chains of opposite type doubles the periodicity within a layer and induces the possibility for intrinsic disorder in the chain layer stacking sequence. The planar superstructure and a staggered stacking of the tetrahedral chain layers is found irrespective of the rest of the intergrowth structure. Superstructure ordering in the case of Co substitution is more perfect than for the Ga substitution.