Affiliation: | a Kernforschungszentrum Karlsruhe, Institut für Technische Physik, W-7500, Karlsruhe, Germany b Kernforschungszentrum Karlsruhe, Institut für Nukleare Festörperphysik, W-7500, Karlsruhe, Germany c Universität Karlsruhe, Fakultät für Physik, W-7500, Karlsruhe, Germany |
Abstract: | X-ray diffraction, resistivity, AC and DC magnetization data on high-quality single crystals of YBa2Cu3O7−δ are presented. We demonstrate that for δ<0.08, the (0 0 l) diffraction lines are split into two, indicating that at these high oxygen concentrations the crystals are no longer single phase but actually consist of two (or more) different phases with slightly different c-axis parameters. In the two-phase region, the electrical resistivity and the AC and DC magnetic susceptibilities show a broadening of the superconducting transition. This broadening is thought to be due to the proximity effect or strains in two finely dispersed phases with slightly different transition temperatures. |