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O: Fachverband Oberflächenphysik

O 70: Poster Wednesday: Electronic Structure

O 70.10: Poster

Mittwoch, 3. April 2019, 17:45–20:00, Poster B2

Proton uptake in the mixed ionic and electronic conductor BaFeO3-x — •Maximilian F. Hoedl, Rotraut Merkle, Eugene A. Kotomin, and Joachim Maier — Max Planck Institute for Solid State Research, Stuttgart, Germany

Many solid oxides containing oxygen vacancies can dissociatively absorb water leading to mobile protonic defects (hydroxide ions on oxide ion sites) in the lattice. The magnitude of water uptake appears to be determined by the basicity of the oxide ions in the solid. However, recent experimental studies suggest that in ionic-electronic mixed conductors such as BaFeO3-x perovskites, the water uptake can be disfavored by an interaction between protons and electron holes.[1] We present the results of first-principles DFT+U and HSE06 calculations on the interplay between the complex electronic structure and the water uptake in BaFeO3-x. The strong correlation effects of Fe3d electrons lead to a significant energy separation of spin-up and spin-down sub-bands. The spin-up band eventually falls below the O2p states and thus triggers a negative charge transfer from the oxide ions to the iron ions, creating holes in the O2p valence band. This reduces the negative charge on the oxide ions and the oxide ion basicity. The calculated hydration enthalpies depend on the hole concentration varying between zero for BaFeO3 and about -1 eV for BaFeO2.6. [1] R. Zohourian et al., Adv. Funct. Mater. 2018, 28, 1801241