Naohiro Nishikawa

Enhanced Critical Current in Tl-Ba-Ca-Cu-O Superconductors Prepared by Diffusion Process with Fluorine Addition

In the Tl-Ba-Ca-Cu-O (TBCCO) diffusion composites, critical current (I c) at 77 K is significantly improved by fluorine (F) addition to the coating layer. The F addition decreases the degradation of I c under magnetic field at 77 K, and shifts the irreversibility lines to higher temperatures. The X-ray diffraction study reveals that F addition promotes the phase transformation from 2223 to 1223. Meanwhile, annealing in flowing O2 at 550° C-600° C also increases I c at 77 K. O2 annealing seems to improve the weak links between superconducting grains. The largest transport critical current density (J c) of the specimen with F addition and O2 annealing exceeds 10000 A/cm2 at 77 K. In the present TBCCO diffusion composites with F addition, the effect of phase transformation on I c performance has been clearly observed.