Modelling of point defects in anisotropic media with an application to ferroelectrics

Ferroelectric materials are used in a wide field of applications and can be found in actuators, sensors and in electromechanical devices with great precision. Because of high cyclic loading during life time, fatigue phenomena occur, involving material degradation and a decrease of the electromechanical coupling capability. The causes are assumed to be ionic and electronic charge carriers, which interact with each other, with microstructural elements in the bulk and with interfaces. Accumulation of defects can primarily lead to degradation, or finally to mechanical damage and dissociation reactions.In order to get a better understanding of the defect accumulation processes, the defect accumulation can be described in continuum models, e.g. phase field formulations. The aim of this paper is to obtain the defect parameters used by comparing the results of molecular dynamics (MD) simulations with the continuous spatial fields. Transferring data from the atomic to the continuum level is a field of active research. On the atomic level, Coulomb–interaction causes a displacement field incompatible to an elastic solution. In order to circumvent this difficulty, the volume expansion or contraction of a volume around the defect is used to determine defect parameters.