Praeparation hochtexturierter Keramiken. Teilvorhaben: Praeparation, chemische Physik, Charakterisierung und Analyse von supraleitenden duennen Schichten und hochtexturierten Keramiken Abschlussbericht

The high T_c-superconductors YBa_2Cu_3O_7 (YBCO) and BSCC 2212 and 2223 as well as material systems with similar electronic structure such as (LiNi)O were investigated. Sintered or partially melted bulk samples of YBCO on the one hand, wires and tapes of BSCC on the other hand were produced. In the latter case, powder in tube method and sputtering were used. In coorperation with Villeroy and Boch, textured wires were received by extrusion method. But also the experiments with powder in tube technology and with sputtering of BSCC onto Ni/NiO/foils, lead to samples of an extreme texture. In these cases critical currents of more than 10"4 A/cm"2 could be obtained. Concerning bulk samples, it was possible by use of water-free slurry, to produce partially melted HTSC in every geometry. With the aid of physico-chemical methods, the importance of one-and two-dimensional faults for the production process of BSCC 2223 could be confirmed. The investigation of model-systems with an electronic structure similar to the HTSC gives numerous interesting physical results, but unfortunately no evidence for new HTSC-systems. Crystallographic methods are handicapped by the insufficient quality of HTSC-single crystals. But nevertheless, it can be supposed that for YBCO a 3-dimensional X-Y-model holds and that in the temperature range above T_c, - at least locally - some non-centrosymmetry exists. Finally, by theoretical investigations, stability and phase transitions in the fluxoid-system and the dynamics of the flux lines were studied. (orig.)Available from TIB Hannover: F95B2177+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Forschung und Technologie (BMFT), Bonn (Germany)DEGerman