ANNEALING OF TWEED MICROSTRUCTURE IN HIGH-TC SUPERCONDUCTORS STUDIED BY A COMPUTER-SIMULATION

The development of tweed texture during annealing is investigated using computer simulation. The model is a two-dimensional one corresponding to an oxygen deficit layer of a higher temperature superconducting crystal of YBa2Cu3O7. The model may be taken as generic, including three dimensional systems, with regard to its semiquantitative behaviour and shows a ferroelastic phase transition due to local strains connected with the oxygen ordering. After quenching from a high temperature, a pronounced {1, 1} micro-twinning appears. It starts from a fine irregular tweed-like pattern, with the spacing between domain walls becoming more regular while coarsening during the anneal. Annealing at lower temperatures, but not near T(c), produces an intermediate stripe structure before annealing to a single domain. From the rate at which the distance between domain walls increases, a temperature-time-transition (T-T-T) diagram has been constructed which shows strong similarities to those obtained from experiments. So do the other features mentioned.