Retrieval of T-c in Y0.9Ca0.1Ba2Cu2.85Re0.15Oz

Combined effect of Ca and Re substitution, respectively, at Y and Cu-sites in YBa2Cu3Oz has been investigated. X-ray photoelectron spectroscopy (XPS) measurements reveal that Re ion exists in hexavalent state in these samples . In this study, we are able to show that the suppression of superconductin g transition temperature (T-c) in YBa2Cu2.85Re0.15Oz (T-c = 63 K) is attrib uted to reduced amount of charge transfer from Cu(I)-chain sites to Cu(II) planes caused by Re6+ ions and the revival of T-c upon Ca-substitution in Y 0.9Ca0.1Ba2Cu2.85Re0.15Oz (T-c = 89 K) is due to the favorable hole inducti on mechanism. (C) 1999 Elsevier Science Ltd. All rights reserved.