Study of the superconducting transition at high pulsed current of bulk Bi-2223 sintered and textured by hot forging

In this study, the transition of Bi1.8Pb0.4Sr2Ca2.2Cu3O10.3+x ceramics in the form of both textured and sintered bars is investigated at 77 K using high pulsed currents with a duration varying from 1.25 to 20 ms, Two types of behaviour are observed: (i) When the average temperature T of the sample is lower than T-c = 110 K, a critical current is recovered at the end of the pulse, probably because of good thermal exchange between the sample surface and the bath and because the critical current density exists up to 110 K; (ii) above this temperature, the sample remains normal after the pulse because the energy dissipated is too high. No deterioration in the sample is observed and experiments can be reproducibly repeated. The maximum instantaneous power applied to the material is 140 GW/m(3) and the maximum energy per unit volume transmitted to the sample after a 20 ms pulse is 925 MJ/m(3). V(I) curves for sintered and textured samples are compared. At 15 times I-c, the measured electric fields are 1000 V/m and 400 V/m for textured and sintered samples, respectively. Using specific heat data and assuming adiabatic heating, the average temperature reached after pulse is calculated. Resistivity curves are obtained for sintered and textured materials which are in good agreement with classical measurements on small samples. (C) 1997 Elsevier Science B.V.