Effect of 3d-metal sulfide doping on the superconducting properties of Bi-2212 superconductors

In the present work, we have studied the effect of 3d metal sulfide doping on the superconducting properties of the Bi-2212 superconductors with the nominal composition Bi_2.1Sr_2.1Ca_0.8[(CuO)_1-x(MS)_x┐<span>2/O_6+δ, where M = Ni, Cu, Zn, Ti. The samples were synthesized by solid state reaction process. Structural and magnetic characterization was carried out using x-ray diffractometry and magnetic susceptibility measurements. All the samples exhibited stabilization of superconducting Bi-2212 phase and reduction of superconducting transition temperature T_c. ZnS and TiS₂ substitution for CuO planes and modification of oxygen content due to S substitution on O places jointly produce strong localization of charge carriers and at the same time improve the hole concentration of the system. These combined phenomena are responsible for the deterioration of superconductivity of ZnS and TiS₂ doped Bi-2212 superconductors.