Ion-size effect on normal-state transport properties in R(0.8)Pr(0.2)Ba(2)Cu(3)O(7-gamma) systems (R=Yb, Er, Dy, Gd, Eu, and Nd)

We report detailed studies of the normal-state resistivity and the Hall-effect in bulk R(0.8)Pr(0.2)Ba(2)Cu(3)O(7-delta) samples (R=Yb, Er, Dy, Gd, Eu, and Nd). We find a linear temperature dependence of the normal-state resistivity rho(u) and the Hall number n(H) above T-c in these systems. At a constant temperature both rho(n) and n(H) are linearly dependent on the ion-size of the rare earth, viz., the larger R(3+) ionic radius, the larger rho(n) but the lower n(H). The cotangent of the Hall angle follows a universal T-2 dependence, i.e., cot theta(H)=alpha T-2+ C. Both the slope cu and the quantity C is insensitive to the R ion and remains almost constant. On the basis of our data we propose a T-c-n(H) diagram which manifests an ''underdoping'' behavior of R(0.8)Pr(0.2)Ba(2)CU(3)O(7-y) systems. We suggest that the strong hybridization between the 4f states of the Pr ion and the conduction-band states in CuO2 planes, leading to hole localization and pair breaking, are the mechanism for the suppression of superconductivity in R(1-x)Pr(x)Ba(2)Cu(3)O(7-y) systems.