An enhancement of T_c, from 45 K to 70 K, via Cd substitution in (Pb, Cu)Sr₂(Ca, Y)Cu₂O_7-δ

An enhancement in the superconducting transition temperature, T_c, from 45 K to 70 K, has been discovered during the course of our investigation of Cd-doping of the Pb-based 1212 superconductors. Specifically, we have attempted to synthesize a material with nominal composition (Pb_0.5Cd_0.5)Sr₂(Ca_0.5Y_0.5)Cu₂O_7-δ, derived from the lead cuprate superconductor (Pb_0.7Cu_0.3)Sr₂(Ca_0.5Y_0.5)Cu₂O_7-δ. From X-ray and electron diffraction, coupled with energy-dispersive X-ray emission spectrometry, we can identify the phase responsible for the 70 K superconductivity to be (Pb_0.67(2)Cd_0.33(5))Sr_2.1(1)(Cd_0.20(3)Ca_0.33(3)Y_0.48(4))Cu₂O_7-δ. Thus, we propose substitution of Cd both for Cu, in the rock salt-type (Pb, Cu)O layers, and Ca, in the Ca_0.5Y_0.5 lattice sites. No superlattice spots or streaks were observed in the electron diffraction experiments along the a^*, b^* and c^* directions in the Cd-substituted material.