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O: Fachverband Oberflächenphysik
O 20: Oxides II: Structures, Interactions and Reducibility
O 20.4: Vortrag
Montag, 16. März 2020, 16:30–16:45, WIL B321
ZrO2−δ thin films: Oxygen-deficient, but not reduced — Peter Lackner, Sabrina Mayr, Josef Redinger, Ulrike Diebold, and •Michael Schmid — Institute of Applied Physics, TU Wien, Vienna, Austria
Zirconia (ZrO2) has a wide range of applications, as an engineering material, in solid-state electrochemistry (gas sensors, solid oxide fuel cells), and as a catalyst support. We have studied thin films (≈ 5 ML) sputter-deposited in ultrahigh vacuum on metal substrates [1]. As-deposited films are slightly oxygen-deficient, which leads to a pronounced core level shift in x-ray photoelectron spectroscopy (XPS). This is caused by positively charged oxygen vacancies (VO••) shifting the electrostatic potential [2]. The XPS results indicate a preference for vacancy formation near the interface, in agreement with density functional theory (DFT) calculations. Full oxidation of the films is possible via oxygen spillover from a metal [2]. The positive VO••s present in the vicinity of the metal support have much lower formation energies than neutral VOs. Thus, oxygen-deficient films can form on a metal under conditions where bulk ZrO2 would remain stoichiometric. Due to charge transfer from the VO••s to the substrate, Zr can retain its preferred 4+ charge state. In other words, the Zr in metal-supported, oxygen-deficient ZrO2−δ films is not reduced.
[1] P. Lackner et al., Surf. Sci. 679, 180 (2019).
[2] P. Lackner et al., Phys. Chem. Chem. Phys. 21, 17613 (2019).