P(O/sub 2/)-T phase diagrams and properties of Ln/sub 2/Ba/sub 4/Cu/sub 7/O/sub 15-δ/ compounds (Ln=Dy,Er,Eu,Gd,Nd,Pr,Sm,Y and Yb)

Oxygen pressure-temperature phase diagrams for Ln/sub 2/Ba/sub 4/Cu/sub 7/O/sub 15-/spl delta// (Ln-247) compounds (Ln=Er,Eu,Gd,Y and Yb) in the pressure range 2-32 bars of oxygen and temperature range 900-990/spl deg/C were studied. The required pressures for Ln-247 single phase synthesis are much lower than was previously found. In addition, phase-pure Ln-247 (Ln=Dy,Nd,Pr and Sm) samples were prepared at high oxygen pressure. The temperatures of the superconducting transition (T/sub c/) for fully oxygen loaded Ln-247 samples are in the range 63-94 K, except for Pr-247 which is not superconducting at temperatures above 4.2 K. These transition temperatures are, for the wider range of rare earth, considerably higher than previously reported. Evidence is presented for progressive underdoping of carriers with increasing rare earth ionic radius, suggesting that T/sub c/ has not been maximized.