Regensburg 2013 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

DF: Fachverband Dielektrische Festkörper

DF 19: Poster 2

DF 19.15: Poster

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

Simulation of the melting temperature reduction of TiO₂ by oxygen deficiency — •Jason Marx, Jan Michael Knaup, and Thomas Frauenheim — BCCMS, Universität Bremen, Germany

The memristive effect in TiO₂ is governed by the externally driven migration of oxygen in a reduced bulk oxide. In the unipolar switching regime, this defect migration leads to the formation and dissolution of metallic Ti₄O₇ nanofilaments through the insulating bulk TiO_2−x. The mechanism of this phase transition is so far not understood at all. One possibility is the local melting of the bulk titania which is usually either amorphous or in the rutile structure followed crystallization into the Ti₄O₇ Magnéli phase upon cooling. As an initial step towards understanding the formation of Magnéli phase nanofilaments, we perform Density-Functional based Tight-Binding (DFTB) modeluclar dynamics (MD) simulations of bulk TiO_2−x at defect concentrations ranging from 0 to the equivalent of Ti₄O₇ stoichiometry at constant cell volume. From the particle trajectories we deduce the melting point by analyzing the RDF, the self-diffusion coefficient and the Linemann index. Special care is taken to analyze the actual dynamics properties of the material, instead of thermostat artifacts. We find a significant lowering of the the melting temperature with rising defect concentration. This lowering is larger than can be explained by the reduction in excluded volume alone. The results indicate that local variations in defect concentration leading to local melting point variations play an important role in the filament formation process.