SUPPRESSION OF SUPERCONDUCTIVITY IN THE OXIDE SYSTEMS R1-XPRXBA2CU3O7-Y (R = SM, GD, AND TM)

Superconductivity in the 90-K range is observed in most of the orthorhombic RBa2Cu3O7-y compounds (R being rare-earth elements and Y). However, the isostructural Pr compound is not superconducting, either due to the 4+ state of Pr whereby the extra electron from Pr fills the Cu-O band, or due to the hybridization of the Pr 4f states with the O 2p-Cu 3d states, or due to a combination of the two. The compounds R1-xPrxBa2Cu3O7-y (R = Sm, Gd, and Tm; 0.0 less-than-or-equal-to x less-than-or-equal-to 1.0) have been prepared and examined for superconductivity. It is observed that the critical Pr concentration required to suppress superconductivity depends on the R ion, varying from x congruent-to 0.32 in the Sm-Pr system to x congruent-to 0.6 in the Tm-Pr system. Band filling due to Pr4+ is expected to be nearly the same in all the compounds and cannot solely account for the strong dependence of the critical Pr concentration on R. Instead, the hybridization mentioned above may explain these results. The T(c) data are analyzed on the basis of the Abrikosov-Gor'kov pair-breaking theory due to magnetic Pr3+ ions.