On the effect of Cd doping and Cd-La codoping in YBa 2Cu 3O 7 − δ

Abstract

Phase stability and superconducting properties of ceramic samples of nominal composition Y 1 − x Cd x Ba 2Cu 3O 7 − δ (Cd doped) and Y 1 − x Cd x Ba 2 − x La x Cu 3O 7 − δ (Cd-La codoped) were investigated for 0.0 ≤ x ≤ 1.0. The formation of secondary phases was observed for all samples containing Cd. The impurity peaks in the XRD patterns of Cd doped samples with x ≤ 0.15 disappeared upon annealing above 800 °C in argon and appeared on re-annealing above 700 °C in oxygen. However, the disappearance of the impurity peaks did not ascertain single phase formation. The electrical properties of Cd doped and Cd-La codoped samples are presented. Semi-quantitative energy dispersive X-ray (EDX) analyses on Y 1 − x Cd x Ba 2 − x La x Cu 3O 7 − δ samples showed that Cd substitution occurs only to a limited extent in La rich ( x > 0.6) samples. This partial incorporation of Cd appears to be related to the occupancy of La at the Y-site in a subtle manner. It is shown that the present results on Cd doped samples, concerning the solubility of Cd, are in contrast with the earlier reports.