AN ENHANCEMENT OF TC, FROM 45-K TO 70-K, VIA CD SUBSTITUTION IN (PB,CU)SR2(CA,Y)CU2O7-DELTA

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 (Pb0.5Cd0.5)Sr2(Ca0.5Y0.5)Cu2O7-delta derived from the lead cuprate superconductor (Pb0.7Cu0.3)Sr2(Ca0.5Y0.5)Cu2O7-delta. 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 (Pb0.67(2)Cd0.33(5))Sr2.1(1) (Cd0.20(3)Ca0.33(3)Y0.48(4))Cu2O7-delta. Thus, we propose substitution of Cd both for Cu, in the rock salt-type (Pb, Cu)O layers, and Ca, in the Ca0.5Y0.5 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.