Local Structure and Its Impact on Ionic Conductivity in Cubic Perovskite Protonic Conductor, an Ab-Initio Based cluster Expansion Study

Abstract

Cubic perovskite of ceramics are typical parent structures for proton conducting electrolyte in intermediate-temperature solid oxide fuel cells, e.g. BZCYYb1. Proton conductivity within this type of materials is well known to be affected by hydration capability, as well as proton mobility. Although a few previous experimental characterizations2-5have unveiled a few pieces of information regarding local structures of proton, dopant and vacancy, a systematic and comprehensive understanding of the underline driving-force for local structure evolution is lacking. Similarly, typical ab-initioDFT calculations assume a fixed dopant concentration with very limited configurations in consideration6-12. Atomically, local structure is the fundamental building-block that constitutively determines macroscopic hydration and mobility of ions. By carrying out ab-initiocalculations, with cluster expansion and Monte-Carlo simulations, competition between entropic-driven defect randomization and enthalpic-driven defect agglomeration is discovered. A temperature vs. dopant-concentration phase diagram is generated. Conductivity is a consequence of dopant, vacancy and proton interactions. Although trapping effects acting on vacancy and proton vary among dopants, a statistical average of ionic mobility is generated through the above approach. By using BaHfO3 as the prototype, representative dopants such as In, K, Sc, Y, Gd, Lu are taken as examples. REFERENCES Yang, L.; Wang, S. Z.; Blinn, K.; Liu, M. F.; Liu, Z.; Cheng, Z.; Liu, M. L., Enhanced Sulfur and Coking Tolerance of a Mixed Ion Conductor for SOFCs: BaZr0.1Ce0.7Y0.2-xYbxO3-delta. Science 2009, 326(5949), 126-129. Mburu, C. W.; Gaita, S. M.; Knee, C. S.; Gatari, M. J.; Karlsson, M., Influence of Yttrium Concentration on Local Structure in BaZr1–xYxO3−δ Based Proton Conductors. The Journal of Physical Chemistry C 2017, 121(30), 16174-16181. Noferini, D.; Koza, M. M.; Rahman, S. M. H.; Evenson, Z.; Nilsen, G. J.; Eriksson, S.; Wildes, A. R.; Karlsson, M., Role of the doping level in localized proton motions in acceptor-doped barium zirconate proton conductors. Phys Chem Chem Phys 2018, 20(20), 13697-13704. Blanc, F.; Sperrin, L.; Lee, D.; Dervisoglu, R.; Yamazaki, Y.; Haile, S. M.; De Paepe, G.; Grey, C. P., Dynamic Nuclear Polarization NMR of Low-gamma Nuclei: Structural Insights into Hydrated Yttrium-Doped BaZrO3. J Phys Chem Lett 2014, 5(14), 2431-6. Giannici, F.; Shirpour, M.; Longo, A.; Martorana, A.; Merkle, R.; Maier, J., Long-Range and Short-Range Structure of Proton-Conducting Y:BaZrO3. Chemistry of Materials 2011, 23(11), 2994-3002. Hermet, J.; Bottin, F.; Dezanneau, G.; Geneste, G., Thermodynamics of hydration and oxidation in the proton conductor Gd-doped barium cerate from density functional theory calculations. Physical Review B 2012, 85(20). Hermet, J.; Torrent, M.; Bottin, F.; Dezanneau, G.; Geneste, G., Hydrogen diffusion in the protonic conductor BaCe1−xGdxO3−x2from density functional theory. Physical Review B 2013, 87(10). Bévillon, É.; Geneste, G., Hydration properties of BaSn0.875M0.125O3−δ substituted by large dopants (M=In, Y, Gd, and Sm) from first principles. Physical Review B 2008, 77(18). Bévillon, É.; Hermet, J.; Dezanneau, G.; Geneste, G., How dopant size influences the protonic energy landscape in BaSn1−xMxO3−x/2(M = Ga, Sc, In, Y, Gd, La). J. Mater. Chem. A 2014, 2(2), 460-471. Geneste, G.; Amadon, B.; Torrent, M.; Dezanneau, G., DFT+U study of self-trapping, trapping, and mobility of oxygen-type hole polarons in barium stannate. Physical Review B 2017, 96(13). Geneste, G.; Dezanneau, G., Competition between elastic and chemical effects in the doping, defect association, and hydration of barium stannate. Solid State Ionics 2017, 308, 121-132. Geneste, G.; Ottochian, A.; Hermet, J.; Dezanneau, G., Proton transport in barium stannate: classical, semi-classical and quantum regimes. Phys Chem Chem Phys 2015, 17(29), 19104-18.