Effect of Sr/Ba substitution in Gd1−xPrxBaSrCu3O7−δ

Tetragonal Gd1−xPrxBaSrCu3O7−δ (0 ⩽ x ⩽ 1) polycrystalline samples have been prepared by the standard solid-state reaction, and characterized by XRD and SEM. Resistance measurements and XRD patterns show site mixing between rare earth R and Sr is less than R and Ca. Contrary to Gd1−xPrxBa2Cu3O7−δ, a hump on the ρ(T) curve is observed at about 80 K. Based on the resistivity measurements, the effect of Pr substitution in the 1113 structure, in comparison with the 123 structure, on the increase of pseudogap temperature is investigated. The normal state resistivity has been analyzed by the two and three dimensional variable range hopping (2D-VRH and 3D-VRH) and Coulomb gap. For the low concentration of Pr (x < 0.5-0.6, corresponding to the metal-insulator transition), the 2D-VRH is the dominant mechanism, but with the increase of x, the 3D-VRH becomes dominant. The magnetic critical fields are investigated through resistance and magnetoresistance. Samples with Sr have higher pinning energy and critical field compared to the samples with Ca. Also, substitution of Ba by Sr or Ca, causes a strong increase in the superconducting granularity. The magnetoresistance measurements have been analyzed by the Ambegaokar and Halperin phase slip model. The field dependences of the pinning energy and critical current density have been studied for different amounts of Pr doping.