RELATION OF CRITICAL CURRENT-DENSITY TO DIAMAGNETIC MAGNETIZATION IN POLYCRYSTALLINE BIPBSRCACUO

The relation of the critical current density J(c) to the lower critical field H(g) of bulk granular superconductors is quantitatively described. H(g) is the critical field of the full shielding effect of the weak link network and represents the magnetization characteristics of the entire bulk superconductor. The maximum self-field produced by transport critical current in a granular superconductor was found to be approximately equal to H(g). D.c. magnetization measurements show that H(g) less-than-or-equal-to 12 Oe at 77 K for BiPbSrCaCuO superconducting materials prepared by the cast-annealing method. It is a linearly decreasing function of temperature: dH(g)/dT almost-equal-to 0.34 Oe K-1. Many experiments show that the critical current density derived from H(g) for sintered samples with rectangular section agrees with the real transport J(c). This procedure for evaluating J(c) is also suitable for other high T(c) polycrystalline materials.