Berlin 2008 – wissenschaftliches Programm
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DF: Fachverband Dielektrische Festkörper
DF 7: Point defect spectroscopy and engeneering
DF 7.1: Hauptvortrag
Dienstag, 26. Februar 2008, 10:00–10:40, EB 107
Modelling of Point Defects in Ferroelectric Materials — •Karsten Albe1 and Paul Erhart2 — 1Institut f. Materialwissenschaft, Petersenstr. 23, TU Darmstadt — 2Lawrence Livermore National Laboratory, Materials Science Division, USA
The properties of ferroelectric materials and their behavior in the presence of electric fields are intimately related to the presence of defects. Oxygen vacancies, for instance, play a key role in aging and fatigue impeding domain wall motion or by acting as local disturbances of the polarization Experimental investigations of point defect properties either provide averaged bulk data or very localized information and can therefore be ambiguous. Quantum mechanical calculations based on density functional theory (DFT), on the other hand, are capable of providing fundamental insights into the energetics of defects as well as their kinetic and electronic properties. In this contribution, two examples will be discussed. For the prototype material barium titanate (BT), DFT calculations are used for verifying established defect models which have been employed to explain the experimental observations (in particular, conductivity and diffusivity measurements). Moreover, the formation of di-vacancies is explored which is an important ingredient for understanding the deterioration of ferroelectric switchability. In the second part, the energy surface of unbound oxygen vacancies and oxygen vacancies complexed with Fe or Cu in lead titanate (PT) is studied. The results are utilized to interpret recent electron spin resonance experiments and discussed in the context of existing defect models.