Structural characterization of superconducting materials

The activities within the framework of the project centered on finding methods of preparing the various materials of the systems La2xBaxCuO4 in such a manner that by pinpointed variations of the materials' compositions, the transition from the ''hole-based'' superconducting phase to the ''electron-based'' superconducting phase is possible. The results achieved considerably enhance the insight into the crystal chemistry of these systems: The mechanisms of insertion of ions of the alkaline earths (Mg, Ba, Sr, Ca) and the limits of substitution are now fully understood and it was possible to synthesize some compounds of the systems with alkaline earths oxides and copper oxide, their structures having been analysed in monocrystals. In the system YBa2Cu3O7, doping with M=Co, Cu, Al.. achieved microstructures and kinetically produced tweed modulations which have been investigated by a combination of electron microscopy with high-resolution X-ray diffraction. The phase transition from the superconducting, orthorhombic to the tetragonal phase, which is a function of the substitution, could thus be shown in detail and could be correlated with microstructures. Neutron diffraction in powder materials was the technique applied to detect and localize the surplus oxygen in the bismuth - oxide layers in the system of the bismuth containing superconducting materials. Finally, analyses using highly resolved synchrotron radiation combined with neutron diffraction revealed a much refined structural representation of all three structures of the bismuth system. (orig./MM)