Comparing the effects of oxygen content on the superconducting properties of YBa2Cu3Ox and RBa2Cu3Ox ith R = Nd, Eu and Gd

Abstract

Previous studies have shown that a Josephson weak link transition occurs in some YBa2Cu3Ox samples at very low fields, H < HC1. This transition is distinct from the vortex glass-fluid transition which of course occurs for H > HC1. The Josephson weak link transition for YBa2Cu3Ox was observed only in samples annealed in oxygen. Moreover, the transition temperature Tc of YBa2Cu3Ox is also sensitive to oxygen content. Tc is 93 K for air-sintered and vacuum-annealed samples but only 90 K for oxygen-annealed samples. We have extended these studies to RBa2Cu3Ox 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 Tc for RBa2Cu3Ox are not sensitive to oxygen content with Tc 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 RBa2Cu3Ox samples show a single peak at 95 K. Vacuum-annealed YBa2Cu3Ox samples also show a single C/T peak at 93 K, but oxygen-annealed YBa2Cu3Ox samples show two peaks in C/T at 90 and 93 K. © 1999 Elsevier Science B.V. All rights reserved