The bipolaron model in the normal state of Pr-doped GdBa2Cu3O7 superconductors

The normal state resistivities of single phase polycrystalline Gd(Ba2 − xPrx)Cu3O7 + δ and (Gd1 − xPrx)Ba2Cu3O7 − δ samples with x = 0.0, 0.05, 0.10, and 0.15 were investigated. The bipolaron model can explain properly the normal state resistivity of the samples. Gd(Ba2 − xPrx)Cu3O7 + δ samples for the special cases x = 0.1 and 0.15 show different behavior. Based on some previous evidence, this behavior could originate from mis-substitution of Ba atoms at rare earth sites. In Gd(Ba2 − xPrx)Cu3O7 + δ samples, the number of localized carriers increases faster than in (Gd1 − xPrx)Ba2Cu3O7 − δ samples with Pr doping. This shows that the superconductivity suppression by Pr at the Ba site is more destructive than by Pr at the rare earth site.