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Anisotropic Proton and Oxygen Ion Conductivity in Epitaxial Ba 2 In 2 O 5 Thin Films

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Fluri Aline, Gilardi Elisa, Karlsson Maths, Roddatis Vladimir, Bettinelli Marco, Castelli Ivano E., Lippert Thomas, Pergolesi Daniele,
Project The search for low temperature super protonic conductivity
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Original article (peer-reviewed)

Journal The Journal of Physical Chemistry C
Volume (Issue) 121(40)
Page(s) 21797 - 21805
Title of proceedings The Journal of Physical Chemistry C
DOI 10.1021/acs.jpcc.7b02497

Abstract

Solid oxide oxygen ion and proton conductors are a highly important class of materials for renewable energy conversion devices like solid oxide fuel cells. Ba2In2O5 (BIO) exhibits both oxygen ion and proton conduction, in a dry and humid environment, respectively. In a dry environment, the brownmillerite crystal structure of BIO exhibits an ordered oxygen ion sublattice, which has been speculated to result in anisotropic oxygen ion conduction. The hydrated structure of BIO, however, resembles a perovskite and the protons in it were predicted to be ordered in layers. To complement the significant theoretical and experimental efforts recently reported on the potentially anisotropic conductive properties in BIO, we measure here both the proton and oxygen ion conductivity along different crystallographic directions. Using epitaxial thin films with different crystallographic orientations, the charge transport for both charge carriers is shown to be anisotropic. The anisotropy of the oxygen ion conduction can indeed be explained by the layered structure of the oxygen sublattice of BIO. The anisotropic proton conduction, however, further supports the suggested ordering of the protonic defects in the material. The differences in proton conduction along different crystallographic directions attributed to proton ordering in BIO are of a similar extent as those observed along different crystallographic directions in materials where proton ordering is not present but where protons find preferential conduction pathways through chainlike or layered structures.
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