Influences of sinter-forging parameters and texture on the critical transport current density of Bi-Pb-Sr-Ca-Cu-O (2223) superconductors

It is well established that the critical temperature and current density of bulk 2223 superconductors are drastically limited by the presence of low-T -C phases, misalignment of the grains and weak intergranular junctions in t he (a, b) planes. Herein, an optimization of the sinter-forging process of the Bi-Pb-Sr-Ca-Cu-O (2223) superconducting ceramic, synthesized by a rapid sol-gel method, has been performed. The kinetics of formation of the Bi-22 23 phase, which are strongly dependent on the calcination and sintering con ditions, were optimized with a goal to raise the purity of the material up to 95% Bi-2223. The precursor powder was pressed at 1.5 t cm(-2), placed un der uniaxial stress up to 46.8 MPa and then heated, between 830 and 850 deg reesC, remaining below the melting temperature. This process resulted in la rge, well textured samples displaying disorientation of less than 4.8 degre es with respect to the (a, b) plane for 50% of the grains. The sinter-forgi ng parameters (temperature, stress and time under load) and the resulting t exture of the samples were correlated with the critical transport current d ensity, J(c), at 77 K, and self-field. Maximum J(c) values up to 8000 A cm( -2) and critical temperatures, T-C of 108 K were achieved through an optimi zation of the stress and the heat treatment schedules. The results indicate that annealing under a 7.5% O-2/92.5% N-2 atmosphere leads to higher J(c) values.