| Abstract
|
:
|
The objectives of the present thesis were mainly directed towards the development of new preparative procedures, rather than to prepare altogether new high-Tc materials, and to study the effects of compositional variations using measurements such as X-ray Powder Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive X-ray-Spectroscopy (EDX), and Resistance versus Temperature. The conditions for co-precipitation, annealing, pulverization, effects of oxygen atmosphere, reaction with porcelain crucible and other processes were optimized for various compositions. The resistance versus temperature measurements indicate Sr was the best alkaline-earth metal among Ca, Ba and Sr for the ternary La-containing ceramics since substitution or doping of Ca and/or Ba for Sr decreased the Tc of these 21-structures. The XRD, SEM, EDX and Tc measurements for both superconducting and non-superconducting samples are discussed with respect to the cell parameters, grain sizes, morphology, peak intensities, peak positions, single phase and/or multi-phase systems, transition temperature (Tc) transition width and Tc (onset). These characteristics are further related to the compositional variation in the two series of samples studied. (Abstract shortened by UMI.)
|