Sonderforschungsbereich 595

Micromechanical Simulation on Interaction of Point Defects with Domain Structure in Ferroelectrics

J. Prof. B. Xu (Div. Mechanics of functional materials)

In this subproject the interaction of point defects with micro-domain structures in perovskite ferroelectrics will be numerically investigated, in purpose of revealing the fatigue and aging mechanisms related to point defects on a micro-mechanical level. A phase field model will be revised to further incorporate different aspects of point defects and the semiconductor feature of the materials. As the depolarization field will be different in the presence of space charges, for instance, due to ionized point defects and electronic charge carriers, the space charge distribution will be first formulated and considered in the simulations. The influence on the domain structures and their stability will be investigated. Further, migration of point defects was also claimed to be a possible important issue in aging and fatigue. Models will be developed to take into account the transport theory of point defects. A consistent simulation should demonstrate the interaction between point defects and the domain walls, and thus further shed light on the aging and fatigue mechanism. Meanwhile, defect dipoles may be formed when e.g. an oxygen vacancy and an impurity cation are located at one of the faces and the center of a single perovskite unit cell, respectively. Even though oxygen vacancies in defect dipoles are expected to have very low mobility, such defect dipoles induce an extra dipolar electric field in addition to the depolarization fields. As another major work program, the influence of reoriented defect dipoles will be simulated.

In this work cooperation is planned with the subprojects C5, B7 and C1 concerning parameter and formulation and with the subprojects B3, D1 and B7 in terms of result verification.