S. Glenis et al., Comparing the effects of oxygen content on the superconducting properties of YBa2Cu3Ox and RBa2Cu3Ox with R = Nd, Eu and Gd, PHYSICA C, 318, 1999, pp. 624-626
Previous studies have shown that a Josephson weak link transition occurs in
some YBa2Cu3Ox samples at very low fields, H < H-Cl. This transition is di
stinct from the vortex glass-fluid transition which of course occurs for H
> H-Cl. The Josephson weak link transition for YBa2Cu3Ox was observed only
in samples annealed in oxygen. Moreover, the transition temperature T-c of
YBa2Cu3Ox 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 RBa2Cu3Ox samples with R = Nd, Eu and Gd. Li
ke the Y-based systems, all three show the Josephson weak link transition b
ut only for oxygen-annealed samples. Unlike the Y-based system, the values
of T-c for RBa2Cu3Ox are not sensitive to oxygen content with T-c being 95
K for all samples. Moreover, the Y- and R-based systems show different spec
ific 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. (C) 1999 Elsevier Science B.V. All rights
reserved.