Superconductivity of (R_0.4Pr_0.6)_0.5Ca_0.5Ba₂Cu₃O_7-δ (R= La, Pr, Nd, Sm, Eu, Gd and Y) Prepared Under High Pressure

The nearly single phase (R_0.4Pr_0.6)_0.5Ca_0.5Ba₂Cu₃O_7-δ compounds (R= La, Pr, Nd, Sm, Eu, Gd and Y) with T_c about 100 K were prepared under high pressure and high temperature using the cubic anvil apparatus. The T_c is much higher than that of the traditional R-123 superconductors without doping Ca on the rare-earth site. For various rare earths with different ionic radius, the (R_0.4Pr_0.6)_0.5Ca_0.5Ba₂Cu₃O_7-δ compounds have almost the same critical temperature. This is different from the result of the ion-size effect of rare-earth ions in R_1-xPr_xBa₂Cu₃O_7-δ compounds. Our results show that Pr has the same properties as other rare earths in the 123-phase compounds due to the doping of Ca.