Superconducting coupling nature at grain boundaries in BizSrzCaCuzO, glass-ceramics consisting mainly of the low-T, phase was first examined by measuring superconducting properties and temperature or ac field dependence of ac complex susceptibility. It was found from the ac loss peaks that superconducting coupling at grain boundaries was basically characterized by three types of weak links. The weak-link behaviors at grain boundaries depended strongly on cooling conditions after annealing and annealing time and temperature. Particularly, it was found that the weak links at grain boundaries were improved by prolonged annealing at 840°C. The furnace-cooled glass-ceramics obtained by annealing at 820" or 840°C for about 200 h exhibited a critical transport current density (77 K, zero magnetic field) of about 200 A/cmZ. [

We prepared superconducting Bi0.8Pb0.2SrCaCu2O y ceramics using the melt quenching method and examined the effect of annealing conditions on the formation of high-T c phases. It was found from the changes in inductance and X-ray powder diffraction analyses that prolonged annealing at 830°C was very effective in increasing the volume fraction of high-T c phases. The samples annealed at 830°C for 200 h and 250 h in air exhibited superconductivity with a T c(zero)=100 K and critical current densities (77 K, zero magnetic field) of 35∼50 A/cm2.

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