Electronic structure, phase formation, and defect distribution in the Ba(Ce,Fe,Acc)O3-d system investigated by density functional theory calculations

W. Sitte^a, R. Merkle^b, M. F. Hoedl^b, A. Chesnokov^c, D. Gryaznov^c, C. Nader^a, A. Egger^a, E. Bucher^a, E. A. Kotomin^b^,^c, J. Maier^b

^aMontanuniversitaet Leoben, Austria

^bMax Planck Institute for Solid State Research, Stuttgart, Germany, Germany

^cInstitute of Solid State Physics, University of Latvia, Riga, Latvia

Proceedings of 24th International Conference on Solid State Ionics (SSI24)

Emerging Materials for High-Performance Devices

London, United Kingdom, 2024 July 14th - 19th

Organizers: John Kilner and Stephen Skinner

Poster, W. Sitte, 316
Publication date: 10th April 2024

For protonic ceramic fuel and electrolysis cells (PCFC, PCEC), the oxygen electrode (positrode) needs electronic as well as proton conductivity. Since in single-phase triple-conducting Ba(Fe,Acc)O_3-_d perovskites electronic and proton conductivity are mutually conflicting properties,[1] composite materials which decouple proton and electron hole transport into separate phases are an interesting option.

The Ba(Ce,Fe,Acc)O_3-_d system with Acc = Y³⁺ or In³⁺ as dopants exhibits a separation into a Fe-rich and a Ce-rich perovskite phase. STEM-EDX analysis indicates a strong tendency of the acceptors to accumulate in the Fe-rich phase.[2,3] This strongly influences also the proton incorporation of these composites, as it decreases the proton uptake of the cerate phase.

In order to complement the experimental results, the elastic properties of BaFeO₃ and BaCeO₃, the energetics of the phase demixing, and the electronic structure of Ba(Ce_1-xFe_x)O₃ are investigated by DFT+U calculations. The driving forces for the distribution of Sc³⁺, Y³⁺, Ga³⁺, In³⁺ acceptors such as size mismatch of dopant to matrix and acid-base interactions are analysed. Also oxygen vacancies show a high tendency to accumulate in the ferrate phase. The implications of these defect distributions for an optimized design of composite positrode materials are discussed.

Acknowledgements: We thank the Austrian Research Promotion Agency FFG (grant no. 871659), the Latvian Council of Science (grant no. lzp-2021/1-0203) and M-Era.Net HetCat project for funding.

References:

[1] Merkle R., Hoedl M.F.; Raimondi G.; Zohourian R., J. Maier J. Oxides with mixed protonic and electronic conductivity, Ann. Rev. Mater. Res. 2021, 51, 461.

[2] Berger C.; Bucher E.; Merkle R.; Nader C.; Lammer J.; Grogger, Maier J.; Sitte W. Influence of Y-substitution on phase composition and proton uptake of self-generated Ba(Ce,Fe)O3-δ-Ba(Fe,Ce)O3-δ composites, J. Mater. Chem. A, 2022, 10, 2474.

[3] Nader C.; Lammer L.; Egger A.; Berger C.; Sitte W.; Grogger W.; Merkle R.; Maier J.; Bucher E. Phase composition and proton uptake of acceptor-doped self-generated Ba(Ce,Fe)O3-δ – Ba(Fe,Ce)O3-δ composites, Solid State Ionics, 2024, 406, 116474.

Acknowledgements:

We thank the Austrian Research Promotion Agency FFG (grant no. 871659), the Latvian Council of Science (grant no. lzp-2021/1-0203) and M-Era.Net HetCat project for funding.

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