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DF: Fachverband Dielektrische Festkörper

DF 19: Poster 2

DF 19.2: Poster

Mittwoch, 13. März 2013, 15:00–17:30, Poster B2

Free energy barriers of oxygen vacancy migration in TiO₂ — Michael Wehlau, •Jan Michael Knaup, and Thomas Frauenheim — BCCMS, Universität Bremen, Germany

To understand the memristive effect in reduced TiO₂, it is of supreme importance to understand the migration behavior of oxygen vacancy (V_O) defects in the material. A basic building block of this understanding are the free energy barriers of (V_O) migration and the influence of various external driving forces on these barriers. Previous results show that due to the immense dielectric constant of titania, the thermodynamic effect of external electric fields is very small even close to dielectric breakdown. However, since the ionic shifts causing this high permeability may influence the migration barriers, these must be analyzed in detail. We perform meta dynamics simulation of the migration of single (V_O) defetcs in rutile TiO₂, based on the Density-Functional based Tight-Binding (DFTB) method. To this end, we develop generally applicable collective variables that allow drive the dynamics of the vacancy rather than attempting to achieve this effect indirectly by driving surrounding atoms. Our results show that using the right kind of collective variables, meta dynamics is well suited to explore the migration mechanisms point defects in solids. Our findings on the free diffusion of (V_O) are in good agreement with previous results.