Suppression of superconductivity in the oxide systems R_1-xPr_xBa₂Cu₃O_7-y (R=Sm, Gd, and Tm)

Abstract

Superconductivity in the 90-K range is observed in most of the orthorhombic RBa₂Cu₃O_7-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 R_1-xPr_xBa₂Cu₃O_7-y (R=Sm, Gd, and Tm; 0.0≤x≤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 0.32 in the Sm-Pr system to x 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.