Effect of Yb addition on the superconducting properties of (Bi,Pb)-2212 superconductor

The effects of Yb addition on the phase evolution and superconducting properties of (Bi,Pb)-2212 superconductor prepared by solid state synthesis in the polycrystalline form were studied. Yb content of the samples was varied (x = 0-0.5) on a general stoichiometry of Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1YbxOy. Phase analysis by XRD, microstructural examination by SEM, measurements of density and superconducting properties were done to evaluate the relative performance of the samples. A Yb containing secondary phase could be distinguished from XRD analysis from Yb > 0.3 in the stoichiometric level. Microstructural examination showed clear and distinct morphological variation with Yb stoichiometry and a secondary phase with round edged grains was observed in the microstructure of Yb added samples. The critical current density (JC) and superconducting transition temperature (TC) of all the Yb added samples were found to be higher than that of the pure sample. A maximum TC-onset of 94.5 K and a maximum JC 688 A/cm2 has been observed for the sample with Yb = 0.2 in the stoichiometric level. Above this level TC and JC began to reduce, may be due to secondary phase formation.