Comprehensive Study of Pr-Doped GdBa2Cu3O7—y System

Abstract

An extensive study of the magnetic, electrical transport, and structural properties of the normal and superconducting states of Gd1—xPrxBa2Cu3O7—y (GdPr−123) is presented. Ceramic compounds have been synthesized by the solid state reaction technique, and characterized by XRD, SEM, TGA, and DT techniques. The parent compound GdBa2Cu3O7—y (Gd−123) is a high-Tc superconductor and the endpoint compound, PrBa2Cu3O7—y (Pr−123) is a magnetic insulator, both having the crystal structures isomorphic to the 123 phase structure. The superconducting transition temperature is reduced with increasing Pr content in a non-linear manner, in contrast to the Abrikosov-Gorkov pair breaking theory. A metal–insulator transition is observed at the critical Pr content, xcr ≈︂ 0.45, at which superconductivity completely disappears. Magnetic susceptibility measurements show that the nominal Pr valence is 3.86+, independent of the Pr content. The metal–insulator transition in this system is similar to that in the oxygen-deficient RBa2Cu3O7—y (R−123) system. Based on this resemblance, we suggest that Pr doping reduces the carrier concentration (either by hole filling/localization or changes in the band structure) similar to the deoxygenated case. Hence, the environment surrounding the Cu–O layers is important to high-Tc superconductivity (HTSC). In this sense, HTSC cannot completely be two dimensional feature. A chain–plane correlation (CPC) effect is plausible. The normal state conduction mechanism has been interpreted by the quantum percolation theory based on localized states. Localization is probably caused by the Pr valence fluctuations in the GdPr−123 system.