INCORPORATION OF PR IN YBA2CU3O7-DELTA - ELECTRONIC EFFECTS ON SUPERCONDUCTIVITY

The complete replacement of Y in Y-Ba-Cu-O superconductors by the trivalent rare-earths La-Lu, with the exception of Ce, Pr and Tb, yields a superconducting phase with a critical temperature (T//c) almost identical to that reported for the yttrium compound. This is somewhat surprising as most of these ions carry significant magnetic moments, the presence of which rapidly decreases T//c in ordinary superconductors. The three exceptions noted, Ce, Pr and Tb, are the rare-earth ions which have a stable tetravalent state. In this paper, the authors present the results of a study of the structure and transport properties of the series of compounds Y//1// minus //xPr//xBa//2Cu//3O//7// minus // delta (x equals 0-1. 0), in which they observe a monotonic decrease in T//c and eventually a metal-insulator transition with increasing Pr concentration. To date, this is the only rare-earth ion which has been found substantially to alter T//c upon partial substitution for Y.