Magnetization, Transport and Structural Studies of Tl-Ca-Ba-Cu-O: Bulk Ceramics, Single Crystals, and Polycrystalline Thin Films.

摘要

A detailed investigation of the Tl-Ca-Ba-Cu-O system of high temperature superconductors is presented including static magnetization, electrical transport, structural and processing data for sintered and melted bulk ceramics, single crystals, and polycrystalline thin films. This system is shown by x-ray diffraction and energy dispersive x-ray analysis to have at least five distinct superconducting phase containing either two or three Cu-O sheets separated by one or two Tl-O planes. Bulk ceramic Tl-2223 has a Meissner effect up to 124 K and zero resistance up to 120 K, but transition temperatures are found to be a strong function of processing even for single crystals. Magnetization versus field data suggest weak flux pinning in all samples above 30 K. Melt processed bulk ceramics of Tl-2223 have transport critical current densities >5000 A/cm sup 2 at 76 K with modest magnetic field dependence, indicating strong intergranular links which are not present in Y-123. This is also observed for unoriented polycrystalline thin films. Tl-2223 films have critical current densities at 76 K up to 240,000 A/cm sup 2 with a modest dependence on in-plane magnetic fields, implying negligible effects of grain boundary Josephson junctions. 29 refs., 9 figs., 1 tab. (ERA citation 14:004748)