We studied the influence of the intermediate rolling deformation on the residual crack network and critical current density in multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes. Although an intermediate rolling step between heat treatment is generally beneficial in raising the critical current density, it also has the negative effect of causing cracking. Cracking was evaluated both by magneto optical imaging and by ultrasonic fracture of extracted filaments. We found that the characteristic fragment size was sensitive to both roll diameter and reduction percentage, decreasing from ~210 µm for a 10% reduction to ~115 µm for a ~20% reduction with 152 mm diameter rolls. At a constant 10% reduction, the fragment size decreased from ~210 µm to ~140 µm when changing from 152 mm to 38 mm diameter rolls. We conclude that intermediate deformation is positive in so far as it decreases the filament porosity, but that it cannot reduce this too much without introducing more cracking than can be healed in subsequent heat treatment. The critical current density thus maximizes at an intermediate deformation that counterbalances these two oppositely directed influences on the filament connectivity.
Abstract-A developed to two-layer electrodeposition process was deposit biaxially textured thallium-oxide superconductor films on Ag-coated, single-crystal substrates. Transport measurements for the electrodeposited, thalliumoxide-based superconductor films show values above lo6A/cm2 at 77K in zero field. In this paper we are reporting magneto-optical imaging data on electrodeposited 1223 thallium-oxide superconductor films. Magneto-optical imaging provides insight into the nature of current flow in the T1-oxide superconductor, and thus will help us to improve the critical current density in bulk high-temperature superconductor wire or tape.
Previously we reported on a two-layer electrodeposition process of thallium oxide superconductors that showed transport critical current density above 10 6 A/cm 2 at 77 K in zero field. In this article, we report our effort to convert an electrodeposited thick film of (Tl,Bi,Pb) 2 (Sr,Ba) 2 Ca 1 Cu 2 O x to (Hg,Bi,Pb) 2 (Sr,Ba) 2 Ca 1 Cu 2 O x by the cation-exchange process. We are also reporting magneto-optical imaging data on Tl oxide superconductor films, which are compared with YBCO. Magneto-optical imaging provides insight into the nature of current flow in the Tl oxide superconductor, and thus, will help us to improve the critical current density in bulk high-temperature superconductor wire or tape.
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