EFFECT OF ZN DOPING ON THE SUPERCONDUCTIVITY OF RBA2CU3-XZNXO7-Y (R = YB, ER, Y, DY, GD, EU, SM AND ND)

Zn, having a definite valence state and filled 3d levels, is used for substituting Cu sites in RBa2Cu3-xZnxO7-y (R=Yb, Er, Y, Dy, Gd, Eu, Sm and Nd). Substitution of Zn for Cu in these systems causes a rapid nearly linear suppression of the superconducting transition temperature T(c). All the RBa2Cu3-xZnxO7-y samples are essentially single phase and retain the orthorhombic structure in the range of substitution (0 less-than-or-equal-to x less-than-or-equal-to 0.1). The reduction of T(c) by Zn doping in RBa2Cu3-xZnxO7-y was found to be strongly dependent on the ionic radius of the rare-earth element R. The superconducting-nonsuperconducting transition accompanied by a transition into the semiconducting phase in these systems is interpreted in terms of a Mott transition.