PRECIPITATION AND PINNING IN CA AND SR-RICH HIGH-T-C SUPERCONDUCTING BI2SR2CACU2O8 CERAMICS

From a consideration of the phase equilibrium diagram of the system Bi 2O3-SrO-CaO-CuO, a simple annealing procedure was developed to precipi tate Bi2+xSr2-xCuO6+d, Sr-14 Cu-24 O-41-x, and Bi2Sr3O6 in high-temper ature superconducting Sr-rich ''Bi2Sr2CaCu2O8'' ceramics and Ca2CuO3 a nd a liquid in Ca-rich ''Bi2Sr2CaCu2O8'' ceramics. The transformation results in an increase of the critical current density of which is bel ieved to express improved pinning properties of the superconducting cr ystals, in particular an increased pinning energy, which reduces the p robability for thermally activated depinning. Possible pinning centers which were introduced during precipitation of the second phases are t he surface of the precipitates.