ENHANCEMENT OF CRITICAL CURRENT IN MELT PROCESSED BI2SR2CACU2O8 BY IRRADIATION WITH 400 MEV OXYGEN IONS

Dense melt processed Bi2S2CaCu2O8 superconductor was irradiated below Tc with 400 MeV oxygen ions up to a dose of 1.55 × 1015 cm-2. Nearly linear with the dose we found a drop in Tc of 7 K and an increase of resistivity of 37% which recovered partly during annealing at 300 K. Irradiation and annealing did not alter the transition width. After irradiation the irreversible magnetization showed a marked increase at low temperatures, while the adverse effect of Tc reduction seemed to prevail for T > 60 K. On the other hand the logarithmic time decay 1/M dM/d ln t was nearly unchanged. This indicates, that the irradiation induced defects act as additional pinning centers with an activation energy U close to that of the intrinsic defects. In contrast to magnetization currents, irradiation was found to enhance the critical transport current density jc(B,T) mainly at higher temperatures. In particular the marked decrease of jc with field, which was found before irradiation, was reduced. © 1990.