Rare-earth ionic radius dependence of superconductivity in Pr-substituted and oxygen deficient R1-xPrxBa2Cu3O7-y

The suppression effect of superconductivity by Pr substitution correlates s trongly with that by oxygen deficiency in the R1-xPrxBa2Cu3O7-y system, whe re R is Yb, Y, Ho, Dy, Gd and Nd. The larger the value of x(C), the Pr cont ent at which superconductivity disappears, the larger the value of y(C), th e oxygen deficiency at which superconductivity disappears. The decreasing r ate in T-C by Pr substitution ( -dT(C)/dx) decreases with decreasing ionic radius of a rare-earth ion for the Ortho-I phase (T-C > 90 K for x = 0) and also with decreasing oxygen concentration (7 - y) The - dT(C)/dx for the s maller rare-earth ions (R = Yb, Y, Ho and Dy) are nearly independent of ion ic radius for the Ortho-II phase (T-C = 60 K for x = 0). The Pr content dep endence of T-C in (Y0.625La0.375)(1-x)PrxBa2Cu3O7- y, average rare-earth io nic radius of which is equal to that of Gd, coincides well with that in the Gd1-xPrxBa2Cu3O7 -y. The weakened T-C-suppression by Pr in the case of the smaller rare-earth ions is explained by considering the hole transfer effe ct from the Cu(1)O chain toward the Cu(2)O-2 plane according to the differe nce in ionic radius between the rare-earth ions and Pr ion. (C) 2000 Elsevi er Science B.V. All rights reserved.