Comparing the effects of oxygen content on the superconducting properties of YBa 2Cu 3O x and RBa 2Cu 3O x with R=Nd, Eu and Gd

Abstract

Previous studies have shown that a Josephson weak link transition occurs in some YBa 2Cu 3O x samples at very low fields, H< H C1. This transition is distinct from the vortex glass–fluid transition which of course occurs for H> H C1. The Josephson weak link transition for YBa 2Cu 3O x was observed only in samples annealed in oxygen. Moreover, the transition temperature T c of YBa 2Cu 3O x is also sensitive to oxygen content. T c is 93 K for air-sintered and vacuum-annealed samples but only 90 K for oxygen-annealed samples. We have extended these studies to RBa 2Cu 3O x samples with R=Nd, Eu and Gd. Like the Y-based systems, all three show the Josephson weak link transition but only for oxygen-annealed samples. Unlike the Y-based system, the values of T c for RBa 2Cu 3O x are not sensitive to oxygen content with T c being 95 K for all samples. Moreover, the Y- and R-based systems show different specific heat behavior. C/ T vs. T for both oxygen and vacuum-annealed RBa 2Cu 3O x samples show a single peak at 95 K. Vacuum-annealed YBa 2Cu 3O x samples also show a single C/ T peak at 93 K, but oxygen-annealed YBa 2Cu 3O x samples show two peaks in C/ T at 90 and 93 K.