TRANSPORT AND STRUCTURAL-PROPERTIES OF PR1-XCAXBA2CU3O7-DELTA THIN-FILMS GROWN BY PULSED-LASER DEPOSITION

We have studied the transport and structural properties of Pr1-xCaxBa2 Cu3O7-delta thin films grown by pulsed-laser deposition, focusing on C a substitution levels x greater-than-or-equal-to 0.3 for which the bul k material is metastable Films with 0.4 less-than-or-equal-to x less-t han-or-equal-to 0.5 exhibit a superconducting transition due to divale nt cation doping on the rare-earth site. Pr0.5Ca0.5Ba2Cu3O7-delta epit axial thin films exhibit a superconducting onset temperature as high a s 47 K with T(c)(R = 0) = 35 K. X-ray-diffraction and electrical-trans port data suggest that Ca doping levels greater than x = 0.5 are possi ble, although disorder is introduced as the divalent to trivalent cati on ratio becomes large. This work demonstrates that 1:2:3-phase superc onductivity can be achieved by substituting Ca for Pr, without the pre sence in the alloy of Y or any other rare-earth element, R, for which RBa2Cu3O7-delta is superconducting. This result supports the view that hole localization, due to hybridization of the Pr 4f electronic level s with the O 2p orbitals, contributes substantially to the suppression of superconductivity by Pr in PrBa2Cu3O7-delta, and demonstrates that this suppression can be partially compensated by appropriate hole dop ing with Ca.