Abstract
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-y samples (R=Yb, Er, Dy, Gd, Eu, and Nd). We find a linear temperature dependence of the normal-state resistivity p u and the Hall number n H above T c . in these systems. At a constant temperature both p n and n H are linearly dependent on the ion-size of the rare earth, viz., the larger R 3+ ionic radius, the larger p n , but the lower n H . The cotangent of the Hall angle follows a universal T 2 dependence, i.e., cotθ H =αT 2 +C. Both the slope α 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 CuO 2 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.