A direct view at excess electrons in TiO${}_2$ rutile and anatase

Abstract

A combination of Scanning Tunneling Microscopy/Spectroscopy and Density Functional Theory (DFT+U) is used to characterize excess electrons in TiO${}_2$ rutile and anatase, two prototypical materials with identical chemical composition but different crystal lattices. In rutile, excess electrons can localize at any lattice Ti atom, forming a small polaron, which can easily hop to neighboring sites. In contrast, electrons in anatase prefer a free-carrier state, and can only be trapped near oxygen vacancies or form shallow donor states bound to Nb dopants. The present study conclusively explains the differences between the two polymorphs and indicates that even small structural variations in the crystal lattice can lead to a very different behavior.

References in corpus (3)

• Reaction of O2 with Subsurface Oxygen Vacancies on TiO2 Anatase (101)
• Calculations of Hubbard U from first-principles
• (Sub)surface mobility of oxygen vacancies at the TiO${}_2$ anatase (101) surface

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