Structure, site occupancies and superconductivity in NdBa2-xPrxCu3 O7+δ system

Structural and superconducting studies have been carried out on the system NdBa2-xPrxCu3O7+δ (0 ≤ x ≤ 0.6). The system transforms from orthorhombic to tetragonal for x ≥ 0.1 and the oxygen content progressively increases beyond 7 to charge balance the replacement of Ba2+ by Pr3+. The superconducting transition temperature, Tc, decreases faster in this system compared to that in RBa2-xRxCu3O7 system with R Nd, Sm, Eu and Gd. Neutron diffraction studies suggest that Pr has a preference for the Ba site in NdBa2-xPrxCu3O7+δ, but there is some occupancy of Pr at the Nd site also. It is known that Pr suppresses Tc when substituted at the site in RBa2Cu3O7-δ system. Thus in the NdBa2-xPrxCu3O7+δ system, Tc suppression has two contributions: one from Pr at the Nd site and the other from Pr/Nd at the Ba site. This may be responsible for the faster decrease in Tc in the present system. (author)