Influence of chemical substituents on the superconductivity of the system Bi4Ca3Sr3Cu4Oy

The effect of the partial replacement of Bi by Eu, Gd, K and Pb, and Cu by Ni, on the superconducting transition temperature (Tc) of Bi4Ca3Sr3Cu4Oy (y=undetermined) is investigated by DC resistivity (R) and AC susceptibility ( chi ) measurements. Tc is not significantly altered by Eu and Gd substituents (Tc close to 65 K); however, K and Pb substituents tend to enhance the fraction of a phase superconducting around 110 K. Interestingly, for nickel specimens, Tc of a large fraction, as suggested by AC chi data, initially decreases to 40 K with increasing concentration of nickel, followed by an increase, whereas R data shows no appreciable variation of Tc.