Granular metals and superconductors are very interesting, because of their unique properties and applications. One of the methods of preparing such materials is a glass-ceramics route, that is, by annealing of an amorphous solid in the way leading to partial crystallisation. In this work we present the influence of annealing conditions on superconducting properties of (Bi,Pb)-Sr-Ca-Cu-O high T_c superconductors prepared by a glass-ceramic method.
Superconducting (Bi,Pb)-Sr-Ca-Cu-O glass-ceramic samples were obtained by annealing of amorphous (Bi_0.8Pb_0.2)₄Sr₃Ca₃Cu₄O_x at temperatures between 750C and 865C for time intervals from 1 minute to 43 hours. The measurements of the temperature dependence of resistivity in annealed samples were carried out between 3 K and 300 K. Critical current densities were determined from magnetic measurements.
The electrical and superconducting properties of the material change during annealing because oxide superconductors belonging to the bismuth family (Bi,Pb)₂Sr₂CuO_x (2201), (Bi,Pb)₂Sr₂CaCu₂O_x (2212) and (Bi,Pb)₂Sr₂Ca₂Cu₃O_x (2223) crystallise forming a granular metal and superconductor. Low temperature resistivity and magnetic measurements show that during the growth of crystalline phases superconducting properties develop rapidly. Measurements of magnetisation reveal that isolated grains of superconducting 2212 phase form in the first minute of annealing at 850 C. Further development of superconducting phases leads to subsequent improvement of superconducting properties. Properties of the material (e.g. room temperature resistivity, critical temperature, critical current) and kinetics of changes depend on the temperature and time of annealing. The highest critical current densities (10⁶ A/cm² at 5 K in 1 T) were obtained for samples annealed at 850 C for 43 h.