MODIFICATION OF THE OXYGEN-ISOTOPE EFFECT IN HIGH-TEMPERATURE SUPERCONDUCTORS DUE TO TRANSITION-METAL DOPING

We have investigated the effect on the oxygen-isotope-effect parameter alpha0 of transition-metal substitutions at the Cu sites in YBa2Cu3O7 -delta (Y 1:2:3), YBa2Cu4O8 (Y 1:2:4), and Bi2Sr2CaCu2O8 compounds. Th e effects of the dopants are found to be quite diverse. In the case of Zn doping, alpha0 remains small in both Y 1:2:3 and Y 1:2:4 although T(c), is rapidly depressed. On the other hand, doping with Fe or Ni ha s quite different effects in Y 1:2:3 and in Y 1:2:4. Our results sugge st that the modification of the isotope effect depends upon the locati on of the dopant (Cu-O chains versus planes).