COMPUTER-SIMULATION OF THE TWEED MICROSTRUCTURE IN HIGH-TC SUPERCONDUCTORS

The tweed microstructure in the non-stoichiometric crystal of YBa2Cu3O7-delta is studied by computer simulation. A two-dimensional model of 99 x 99 unit cells represents a layer of this crystal with an oxygen deficit and exhibits a ferroelastic tetragonal-orthorhombic phase transition. The simulation allows us to determine the temperature-oxygen-concentration phase diagram. Below the transition temperature the strain fluctuations form a grid of needle-shaped domains, the density of which increases with increasing degree of non-stoichiometry. On quenching, the tweed texture orders through the intermediate stripe phase, to a single orthorhombic domain. Oxygen vacancies, appearing due to non-stoichiometric oxygen concentration, gather along the domain walls, and hence slow down the kinetics of the annealing process.