Abstract
We have investigated the Sr doping effect on the electronic transport behaviour in PrBa2-xSrxCu3Oy and PrBa2-xSrxCu2.7Mo0.3 Oy. With the increase of the doping level, the low-temperature resistivity exhibits a rapid drop at x = 1.0 and, accordingly, the localization radius of carriers (holes) increases significantly. However, a further increase in the doping level does not result in the occurrence of a metallic or superconducting state in the Pr system, although the resistivity still decreases slowly with the increasing doping level. Our results show that Sr doping at the Ba site in PrBa2Cu3Oy plays a role in releasing the holes, which are localized in the Fehrenbacher-Rice states, switching the system from a highly localized state to a modest localized state. Our results also suggest that the superconductivity cannot be restored in PrBa2Cu3Oy by merely using Sr doping at the Ba site.