Structural and superconducting properties of Bi 1.7Pb 0.4Sr 2 − xYb xCa 1.1Cu 2.1O y system

Abstract

The structural, electrical and superconducting properties of Bi 1.7Pb 0.4Sr 2 − x Yb x Ca 1.1Cu 2.1O y 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 Yb 3+ in place of Sr 2+ and consequent change in the hole concentration in the CuO 2 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).