PROBING OXYGEN ORDERING IN YBCO BY IN-SITU HIGH-TEMPERATURE RESISTIVITY AND X-RAY-DIFFRACTION STUDIES

In the high temperature superconducting material yttrium barium copper oxide (YBCO) the basal plane oxygen plays a dominant role in determin ing the superconducting properties of the material. We have carried ou t in situ high temperature measurements of(a) electrical resistivity a nd (b) X-ray diffraction in vacuum as well as in helium atmospheres to probe the nature of ordering of oxygen atoms. While published phase d iagram of temperature vs oxygen concentration in different partial pre ssures allow only a tetragonal phase for the annealing temperatures we have investigated, the experiments point to the coexistence of orthor hombic (OII) and tetragonal phases.