The influence of long reaction time on various properties of monocore Bi-2223/Ag tapes

The mechanisms leading to a maximum of j(c) as a function of reaction time in (Bi,Pb)(2)Sr2Ca2Cu3Ox monofilamentary. tapes are investigated. Various p roperties of tapes previously. reacted 40 hours in air at 837 degrees C, ro lled, and submitted to additional reaction during times varying from 40 to 240 hours were measured. The evolution of morphology, phase assembly, stoic hiometry, weight, critical temperature, critical current and irreversibilit y line is described. XRD and SEM analysis reveal no decomposition of the Bi (2223) phase and no noticeable grain growth in the time window under invest igation. Pb losses as function of reaction time up to 40 % were detected by means of thermogravimetry and EDS, while an increase of T-c from 107.25 to 109.1 K was observed, Transport and magnetic measurements show that the ob served maximum of j(c) at about 180 hours is the result of two competing ef fects: a) an improvement of the quality of grains boundaries and b) a decre ase of the pinning efficiency in the grains.