Abstract:
Prompted by a literature report that thin films of Pr0.5Ca0.5Ba2Cu3O7-δ are superconducting, the structure and bulk properties of orthorhombic Pr1-xCaxBa2Cu3O7-δ and tetragonal PrBa2-xLaxCu3O7-δ have been investigated. Both these systems do not show superconductivity. Tetragonal Pr1-xCaxBaLaCu3O7-δ, on the other hand, shows superconductivity when x=1.0 and 0.8 with onset Tc's of 66 K and 46 K respectively; compositions with x < 0.6 are semiconducting. Since the hole concentration in PrBa2Cu3O6.9, PrBaLaCu3O7.42 and CaBaLaCu3O6.9 are comparable, the absence of superconductivity in the first two cuprates is likely to be due to the location of the 4f level of Pr3+ in the vicinity of the Cu-O band.
