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

Abstract

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 (T-C) and critical current density (J(C)) are found to increase drastically with Yb substitution. Maximum values of T-C and J(C) are observed for x=0.3 and x=0.2 respectively. The increase in T-C and J(C) 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 T-C and J(C) 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)