COMPUTER-SIMULATION OF DOMAIN FORMATION IN CRYSTALS

The phase transitions and the annealing processes simulated by the mol ecular-dynamics technique for KSCN and YBCO crystals are presented. Th e KSCN and YBCO model crystals show co-elastic and ferroelastic phase transitions, respectively. On quenching from disordered phases and sub sequent annealing, tweed microstructures are obtained, which evolve to strip phases with well defined domain walls. Ln KSCN the antiphase bo undaries are arbitrarily oriented. A number of dielectric and ferroela stic crystals possess incommensurately modulated phases, which could b e seen as a sequence of discommensuration planes. The same simulation technique has been used to study the nucleation of topological defects responsible for creation of discommensurations. It is proved that the elastic domain walls favour nucleation of discommensuration planes.