Growth of the Bi-2223 phase after a short nucleation stage at high temperature

A new two-step annealing procedure is investigated in order to accelerate the kinetics of transformation and reaction: a short stage at high temperature (870 degreesC), to induce nucleation of the high-transition temperature phase "2223", is followed by a second stage at lower temperature (830 degreesC) to promote its growth. Magnetic susceptibility measurements on fibres submitted to this heat treatment cycle show a transition onset to superconductivity state at temperatures higher than that observed for samples annealed without nucleation stage. The increase of T-c values are due to the early development of the "2223" phase. Electrical resistance measurements corroborate that this new two-step procedure is an alternative process to develop the "2223" phase without the detrimental effect of liquid-phase formation. (C) 2001 Elsevier Science B.V. All rights reserved.