Rare earth substituted 124 and 247 superconductors

Abstract

Rare earth substitution has given a series of superconducting compounds in which Tc can be correlated with lattice parameters. Eight rare earth compounds with 124 structure, and five with 247 structure, are easily synthesized in oxygen at pressures between 10 and 70 bar. The 247 compounds are stable only within a narrow range of oxygen pressures bounded by the stability regions of the 124 and 123 phases. The Tc's of the 124 and 247 phases vary inversely with ion size. Surprisingly, the 247 compounds have much lower Tc's (45–55 K) than the 124 or 123 parent compounds. The basal plane areas of 247 are larger and orthorhombic distoritions smaller than the corresponding 123 and 124, suggesting weaker bonding in the CuO2 layers.