IMPROVEMENT OF FLUX-PINNING BY THERMOMECHANICAL TREATMENT OF BI-2223 AG SUPERCONDUCTING TAPES/

Measurements of the transport critical current (I-c) in a magnetic fie ld (H), hysteresis loops and a.c. susceptibility were performed on Bi- 2223/Ag tapes that were subjected to different degrees of mechanical d eformation and subsequently sintered. I-c against H for some of the ta pes was also measured at different stages of thermo-mechanical treatme nt. All the measurements (the field of the peak of the pinning force, the irreversibility field obtained from hysteresis loops and the tempe rature of the peak of a.c. susceptibility for different d.c. fields) c learly show an increase of pinning with increase of the degree of mech anical deformation. Measurements of samples at different stages of the rmo-mechanical treatment indicate that the pinning depends not only on the degree of mechanical deformation, but also on the conditions of t he grain growth. Sintering can provide imperfect healing of micro- and nano-cracks, introduced upon mechanical deformation. It is proposed t hat the imperfections introduced by the healing are responsible for th e improvement in flux pinning, and not the dislocations introduced upo n mechanical deformation.