Dresden 2014 – wissenschaftliches Programm
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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.