Structural analysis of the Y2BaCuO5 thermally treated

It is known the YBa2Cu3O7-δ (Y123) prepared by the solid reaction method coexists with a green phase Y2BaCuO5 (Y211). In this work we study the behavior of the Y211 (pure) overheated at 1100oC and 1300oC respectively. The starting sample was prepared by the conventional solid reaction method using appropriate amounts of Y2O3, BaCO3 and CuO; the initial sample was green in color. From the X ray diffractogram (XRD) and using the Rietveld refinement we found that the crystalline structure is orthorhombic and belong to the Pnma spatial group. This is the some structure as the one found by Michael and Raveau. The starting sample was overheated at 1100oC under oxygen pressure of 0.1 atm. According with the XRD, there are no significant variations on its structure. Nevertheless after an overheating of 1300oC in the same oxygen pressure, a new phase Y2O3 with a cubic symmetry together with the original orthorhombic phase is observed by X-ray measurement. In this case, some other impurity phases, which could not be indexed in terms of any phase thus far reported in the Y-Ba-Cu-O system, were detected as minor phases. A morphologic and chemical analysis using a scanning electronic microscope is added. (orig.)