Structural and superconducting properties of Bi1.7Pb0.4Sr2 − xYbxCa1.1Cu2.1Oy system

The structural, electrical and superconducting properties of Bi1.7Pb0.4Sr2 − xYbxCa1.1Cu2.1Oy system has been studied for different Yb concentrations. The samples are prepared by solid state synthesis in the polycrystalline bulk form. Structural analysis by X-ray diffraction, microstructural examination by SEM and measurements of electrical and superconducting properties have been conducted to study the effects of Yb substitution at Sr site. The critical temperature (TC) and critical current density (JC) are found to increase drastically with Yb substitution. Maximum values of TC and JC are observed for x = 0.3 and x = 0.2 respectively. The increase in TC and JC is explained due to the substitution effect of Yb3+ in place of Sr2+ and consequent change in the hole concentration in the CuO2 planes. Above the optimum levels TC and JC begin to reduce due to secondary phase formation. A metal-insulator transition originating from the change of carrier concentration is found to occur at higher doping level (x > 0.5).