Upper critical field and normal-state properties of single-phase Y1−xPrxBa2Cu3O7−γ compounds

Abstract

Substitution of Pr for Y in the ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ system depresses $T_c$, with superconductivity disappearing for x≥0.5. The origin of this $T_c$ depression is still controversial, as is the valence state of the Pr ion. In order to study these problems, single-phase materials were prepared with x=0.0, 0.1, 0.2, 0.3, 0.35, 0.4 0.45, 0.5, 0.6, 0.7, 0.9, and 1.0. Under certain annealing conditions, these types of samples will phase separate into ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{Y}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Pr}}_{\mathit{x}}$ ${\mathrm{Ba}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\gamma }$, showing two transitions in the magnetization, but will still appear single phase from x-ray diffraction. We have overcome this problem through specific annealing conditions of time, temperature, and atmosphere. We find that the superconductivity is strongly suppressed as a function of Pr concentration, with a behavior which is consistent with the classical Abrikosov-Gor’kov pair-breaking theory. The critical fields versus T show a ‘‘bell’’-shaped behavior, which is consistent with the presence of magnetic pair-breaking interactions. The measured temperature dependence of the critical field, $H_{c2}$ near $T_c$, and the Pauli susceptibility, are used to estimate the physical parameters ${\lambda }_{\mathrm{GL}}$, ${\xi }_{\mathrm{GL}}$, and γ.