Superconductivity in Layerd Cuprate (RuI-x_Nbx)Sr2GdCu2O8

A series of layered cuprate (Ru 1_x Nbx)Sr2GdCu2o3 (RuI212) for 0 (less than) x (less than) 1has been synthesized by the solid state reaction method. Powder X-ray diffraction analysis indicates that oxygen flow is important in the formation of the Ru1212 phase and superconductivity in the system. Samples with nominal composition (Ru 1_x Nbx)Sr2GdCu2o3 can be indexed as a tetragonal structure with space group P4/ mmm. The undoped compound exhibits the highest superconducting transition with T e onset 65 k. and T c zero 55 k. Our results also show that c o nse t c zero doping with Nb decreases the normal state conductivity and suppresses superconductivity in the system.