Structural and superconducting properties of Bi1.7Pb0.4Sr2−xGdxCa1.1Cu2.1Oy system

The effect of substitution of the rare earth ion Gd at Sr site of (Bi, Pb)-2212 superconductor has been studied by varying Gd in the stoichiometric level. The samples were prepared by solid-state synthesis route in the polycrystalline bulk form. Phase analyses of the samples by XRD, microstructural examination by SEM, elemental analysis by EDAX and measurements of electrical and superconducting properties have been carried out to assess the effects of substitution. Both the critical temperature (TC) and critical current density (JC) are found to increase with Gd substitution at Sr site and the maximum TC was observed for x = 0.3 in the initial composition Bi1.7Pb0.4Sr2−xGdxCa1.1Cu2.1Oy and the maximum JC for x = 0.2. The increase in TC and JC is explained due to the substitution of Gd3+ in place of Sr2+ and consequent change in chemical and electronic inhomogenities. Above these level TC and JC begin to reduce and a metal–insulator (MI) transition occurs at higher doping levels (x > 0.5).