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O: Fachverband Oberflächenphysik

O 81: Oxide and Insulator Surfaces III

O 81.9: Vortrag

Donnerstag, 3. April 2014, 18:00–18:15, PHY C 213

Small and Large Polarons in TiO₂ Rutile and Anatase — •Martin Setvin¹, Cesare Franchini², Xianfeng Hao¹, Benjamin Daniel¹, Michael Schmid¹, Georg Kresse², and Ulrike Diebold¹ — ¹TU Wien, Vienna, Austria — ²Universität Wien, Viena, Austria

TiO₂ is a prototypical metal oxide and used in photocatalysis, photoelectrochemical (Grätzel) solar cells, and transparent optical conductors. Industrially two forms of TiO₂ are used, rutile and anatase. The behavior of charge carriers is of key importance in virtually all applications of these materials. When excess electrons are added to the conduction band of an oxide, the electron-phonon interaction may result in electron trapping – the formation of either localized (small) or delocalized (large) polarons.

We used a combination of STM, STS and DFT+U to investigate the nature of electron polarons in rutile and anatase. The excess electrons in rutile can localize at any lattice Ti atom, forming a small polaron. The polarons in rutile can easily hop to neighboring sites. Electrons in a perfect anatase lattice prefer delocalized (band-like) solution, while small polarons can only be formed at defects. Large polarons were observed in Nb-doped anatase in vicinity of subsurface Nb dopants. Our results help to understand the different behavior of TiO₂ rutile and anatase in applications.

Work supported by ERC Advanced Research Grant Oxide Surfaces.