The hole concentration per unit cell (p) was measured by using an iodometric titration technique for bulk Gd1-xPrxBa2Cu3O7-y (x = 0.1-0.9) and R0.8Pr0.7Ba2Cu3O7-y (R = Yb, Er, Dy, Gd and Nd) samples. These data were compared with the Hail number per unit cell (nH) at 100 K and superconducting transition temperature (Tc) reported in the literature. We suggest that the hybridization between 4f states of the Pr ion and the conduction band states in CuO2 planes, leading to the hole localization are the mechanism for the suppression of superconductivity in these systems. The correlation between Tc and p cannot be described by the empirical relation observed in many high-Tc oxides.
Physica C: Superconductivity and its Applications 292, pp.53-58