Suppression of superconductivity in the R(Ba_1-zR_z)₂Cu₃O_7+δ (R=Pr,Nd) system

Abstract

Structural and superconducting behavior of samples prepared with the nominal compositions of Nd_1.05(Ba_1-zPr_z)_1.95Cu₃O_7+δ has been investigated by neutron-diffraction and dc magnetization measurements. Neutron data refined by the Reitveld method showed that there is mixing of the rare-earth (R) ions with a substantial fraction of the Pr going to the normal R site in the RBa₂Cu₃O_7+δ-type structure and a corresponding fraction of the Nd going to the Ba site. Structural changes due to the trivalent R ions going to the Ba site are very similar to those observed in the Nd_1+xBa_2-xCu₃O_7+δ(Nd123ss), indicating that Pr behaves like other trivalent R's on the divalent Ba site. Magnetization measurements show that the depression in T_c is more pronounced for the Pr bearing samples than that for Nd123ss for the same number of trivalent ions on the Ba site. However, by correcting the changes in T_c for the depression associated with the fraction of Pr on the R site, the depression in T_c per trivalent ion on the divalent site is found to be identical to that in other light R123ss. Thus the depression in superconductivity in this series of samples is due to two independent effects: (1) Pr on the R site and (2) hole localization due to trivalent R ions on the Ba site. In this respect, Pr on the Ba site appears to behave like all the other trivalent R ions.