Berlin 2015 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 6: Poster Session DF

DF 6.5: Poster

Montag, 16. März 2015, 19:00–21:00, Poster C

Dynamics of Oxygen Vacancies in TiO2 — •Michael Wehlau, Jan M. Knaup, and Thomas Frauenheim — BCCMS Universität Bremen, Germany

Resistive switching materials like titania (TiO2) are potentially capable for applications in next-generation semiconductor devices or as components of artificial neurons. Resistive switching effect of metal oxides is based on phase-change mechanisms induced by accumulation of oxygen vacancy defects (VO) and following transformation of insulating TiO2 into substoichiometric conductive phases. For this reason the VO migration is a crucial mechanism for resistive switching. In this work we investigate the dynamics of oxygen vacancies in two ways. We involve thermodynamics in calculations of the free energy surface by metadynamics and obtain accurate minimum energy paths (MEP) for rutile and anatase. We calculate free energy profiles for the VO diffusion using metadynamics, employing a modified version of the PLUMED code, coupled to DFTB+, which implements a permutation invariant vacancy tracking (PIVOT) collective variable. This method provides a technique for rare event sampling without specifying reaction paths. Furthermore, we also perform nudged elastic band calculations to find the MEP for essential VO transitions using the ab-initio DFT method provided by the vasp code. We find free energy barriers and MEP in good agreement. We also find a strong dependency of the activation energy on the crystallographic direction, the crystal structure and the material density.