Abstract
Acceptor-doped barium zirconate is a promising proton-conducting oxide for various applications, for example, electrolysers, fuel cells or methane-conversion cells. Despite many experimental and theoretical investigations there is, however, only a limited understanding as to how to connect the complex microscopic proton motion and the macroscopic proton conductivity for the full range of acceptor levels, from diluted acceptors to concentrated solid solutions. Here we show that a combination of density functional theory calculations and kinetic Monte Carlo simulations enables this connection. At low concentrations, acceptors trap protons, which results in a decrease of the average proton mobility. With increasing concentration, however, acceptors form nanoscale percolation pathways with low proton migration energies, which leads to a strong increase of the proton mobility and conductivity. Comparing our simulated proton conductivities with experimental values for yttrium-doped barium zirconate yields excellent agreement. We then predict that ordered dopant structures would not only strongly enhance the proton conductivities, but would also enable one- or two-dimensional proton conduction in barium zirconate. Finally, we show how the properties of other dopants influence the proton conductivity.
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Data availability
The data that support the findings of this study are available from M.M. upon reasonable request.
Code availability
The self-written codes iCon and MOCASSIN for the KMC simulations are available from M.M. upon reasonable request.
Change history
09 March 2020
A Correction to this paper has been published: https://doi.org/10.1038/s41563-020-0654-3
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Acknowledgements
The authors gratefully acknowledge the computing time granted by the JARA Vergabegremium and provided on the JARA Partition part of the supercomputer CLAIX at RWTH Aachen University within the projects jara0141 and rwth0189.
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M.M. led the development of the concept and supervised the research. F.M.D. performed the DFT and KMC calculations, collected the data and analysed them. C.A. also performed DFT calculations and contributed data. J.P.A., S.E. and S.G. developed the program MOCASSIN and delivered technical support. J.P.A. also created the simulation cells for the superstructures. S.Y. provided critical suggestions concerning the analytical procedure. M.M. and F.M.D. wrote the paper with contributions from all the authors.
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Draber, F.M., Ader, C., Arnold, J.P. et al. Nanoscale percolation in doped BaZrO3 for high proton mobility. Nat. Mater. 19, 338–346 (2020). https://doi.org/10.1038/s41563-019-0561-7
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DOI: https://doi.org/10.1038/s41563-019-0561-7
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