Superconductivity, intergrain, and intragrain critical current densities of materials

Bulk sintered and powdered samples of the high-temperature superconductive compounds ${\mathrm{Tl}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{1+\mathrm{\delta }}$ (Tl-2:2:2:3) and ${\mathrm{Tl}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_2$ ${\mathrm{O}}_{8+\mathrm{\delta }}$ (Tl-2:1:2:2) have been synthesized with phase purity of approximately 90%. The materials were characterized by x-ray-diffraction, metallographic, and electron microprobe analyses. The electronic and superconductive properties were investigated through measurement of the electrical resistivity and the critical current density $J_c$ using transport methods and by extensive magnetization measurements. Primary results and conclusions are that (1) the intragrain $J_c$ values were large, much larger than the transport values; (2) both sintered and powdered materials exhibited large flux creep; (3) and the $J_c$ decreased exponentially with temperature. These features are qualitatively very similar to those found in the corresponding ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathrm{z}}$ (with z≊7) series of compounds.