RARE-EARTH ION SIZE EFFECT ON RESISTIVITY, SUSCEPTIBILITY, AND SUPERCONDUCTIVITY OF RBA(2)CU(3-X)ZN(X)O(7-Y) (R=YB, ER, Y, DY, GD, EU, SM, AND ND)

A systematic study of Zn doping on the resistivity rho, dc susceptibil ity chi, and superconducting T-c of RBa(2)Cu(3-x)Zn(x)O(7-y) systems ( R=Yb, Er Y, Dy, Gd, Eu, Sm, and Nd, and 0 less than or equal to x less than or equal to 0.3) is reported. X-ray powder diffraction (XRD) sho ws that all samples consist essentially of a single phase and retain t he orthorhombic structure in the range of 0 less than or equal to x le ss than or equal to 0.3 (except for R=Yb in the range of 0 less than o r equal to x less than or equal to 0.15). By analyzing our Raman spect ra and XRD data, Zn atoms are found more likely to substitute on Cu(2) sites. Doping with Zn on the Cu site in these systems causes a rapid nearly linear decrease of T-c as Zn content increases. The reduction o f T-c for RBa(2)Cu(3-x)Zn(x)O(7-y), is found to depend strongly on the ionic radius of the rare-earth element R. This effect resembles the i on size effect on T-c in R(1-x)Pr(x)Ba(2)Cu(3)O(7-y), where Pr substit utes on the R site, and in RBa(2)Cu(3-x)Ga(x)O(7-y), where Ga substitu tes on the Cu(1) sites in Cu-O chains, although in the RBa(2)Cu(3-x)Zn (x)O(7-y) systems Zn is found to be more likely to substitute on the C u(2) sites in Cu-O-2 planes. The suppression of superconductivity by z inc and the rare-earth ion size effect on T-c in these systems is inte rpreted in terms of a Mott spin bipolaron model.