Diamagnetic substitution in LaSCO and YBCO superconductors: study of Cd- and Sn- systems

Substitutions of diamagnetic Cd 2 + and Sn 4+ in YBCO and LaSCO structures have been investigated with the aim of clarifying the reported "anomalous" effects of such elements with respect to other ions with similar electronic structure on the superconductive transition of perovskites. X-ray diffraction, electrical resistivity measurements and EDX analysis were used to investigate the doping-induced structural and resistive effects and to identify secondary phases. Our results indicate that Cd and Sn have a limited solubility in LaSCO and they do not substitute in YBCO. Small Cd-induced effects on LaSCO Tc are explained by assuming a Cd substitution for La, rather than for Cu. Sn, substituting for Cu up to 4 at.%, is as effective as Zn in deteriorating the resistive characteristics of LaSCO.