Incorporation of Pr in YBa₂Cu₃O_7−δ: electronic effects on superconductivity

Abstract

Considerable excitement has been generated by the report of superconductivity above 90 K in a multi-phase Y–Ba–Cu oxide¹. The superconducting phase was subsequently identified as YBa₂Cu₃O_7−δ^2,3. The complete replacement of Y 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^4–7. 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. Here we present the results of a study of the structure and transport properties of the series of compounds Y_1−xPr_xBa₂Cu₃O_7−δ (x = 0−1.0), in which we observe a monotonic decrease in T_c and eventually a metal–nsulator 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.