Suppression of superconductivity in the $R({\mathrm{Ba}}_{1-z}{R}_z{)}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7+\delta }$ ($R$=Pr,Nd) system

Structural and superconducting behavior of samples prepared with the nominal compositions of Nd${}_{1.05}$(Ba${}_{1-z}$Pr${}_z{)}_{1.95}$Cu${}_3$O${}_{7+\delta }$ 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 $\mathrm{}\left(R\right)\mathrm{}$ ions with a substantial fraction of the Pr going to the normal $R$ site in the $R$Ba${}_2$Cu${}_3$O${}_{7+\delta }$-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${}_{1+x}$Ba${}_{2-x}$Cu${}_3$O${}_{7+\delta }$ (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 $R$123ss. 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.