OXYGEN ORDERING IN NONSTOICHIOMETRIC YBCO STUDIED BY MOLECULAR-DYNAMICS TECHNIQUE

A two-dimensional model describing the oxygen ordering in the CuO1-del ta basal plane of YBa2Cu3O7-delta is studied using the molecular-dynam ics technique. The temperature - oxygen-concentration phase diagram is found to consist of a tetragonal phase and two orthorhombic phases, O I and OII. The OII phase occurs in a wide range of oxygen concentratio n. At concentrations greater or lower than 0.5 and at low temperature the OII phase is accompanied by OI and tetragonal precipitates. The co mpeting OI and OII domains slightly disturb the coarsening of the twee d microstructure which is formed after the fast quench from the tetrag onal phase to the low-temperature orthorhombic phase.