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DF: Fachverband Dielektrische Festkörper

DF 12: Electric, Electromechanical and Optical Properties II

DF 12.6: Talk

Friday, March 30, 2007, 12:30–12:50, H11

Association of oxygen vacancies with impurity metal ions in lead titanate: first-principles calculations and kinetic modeling — Paul Erhart¹, R.-A. Eichel², Petra Träskelin³, and •Karsten Albe¹ — ¹TU Darmstadt, Institut für Materialwissenschaft — ²TU Darmstadt, Eduard-Zintl-Institut — ³University of Helsinki, Finland

Oxygen vacancies (V_O) and their associates are widely believed to play an important role in the ageing and the fatigue of ferroelectrics. Knowledge of their energetics is therefore instrumental in order to understand these processes. We have used DFT calculations in order to study the energy landscape for the formation and migration of free and complexed V_O in Cu and Fe doped PbTiO₃. It is found that nearest neighbor configurations are preferred and the migration barriers for V_O in the vicinity of metal impurities are significantly higher than for uncomplexed V_O. These insights permit us to review the assumptions underlying the Arlt-Neumann model for ageing. On the basis of our calculations we present a kinetic model which allows to study the redistribution of free and complexed oxygen vacancies in a tetragonal perovskite. It is shown that the conversion between free and complexed vacancies readily occurs during growth. In the absence of an electric field, one specific impurity atom–vacancy configurations is dominating. Upon application of an oscillating electric field near room temperature, however, a dynamic equilibrium between different impurity atom–vacancy configurations is installed. We propose that the fatigue of ferroelectric material is closely related to this dynamic balance.