The effect of Bi2201 phase on the intergranular critical field and current density in Bi2223 superconductors

The phase equilibria between Bi2201, Bi2212 and Bi2223 were established relative to the sintering temperature. By improving the sintering conditions (temperature, intermediate grindings), a procedure was determined to prevent the formation of Bi2201 phase and also to obtain nearly pure Bi2223 powder. It was found that the residual Bi2201 phase is an important limiting factor of superconducting properties-samples rich in the Bi2201 phase exhibited almost no intergranular critical currents and fields, while the highest superconducting values were found in the samples free of the phase. Magnetic and transport measurements showed that the transport behaviour of the grain boundaries becomes semiconducting in samples sintered at high temperature, in which an increase of the Bi2201 phase content is observed. (C) 2002 Elsevier Science B.V. All rights reserved.