  To design and discover new materials for next-generation energy materials
such as solid-oxide fuel cells (SOFCs), a fundamental understanding of their
ionic properties and behaviors is essential. The potential applicability of a
material for SOFCs is critically determined by the activation energy barrier of
oxygen along various diffusion pathways. In this work, we investigate
interstitial-oxygen (Oi) diffusion in brownmillerite oxide SrCoO2.5, employing
a first-principles approach. Our calculations indicate highly anisotropic ionic
diffusion pathways, which result from its anisotropic crystal structure. The
one-dimensional-ordered oxygen vacancy channels are found to provide the
easiest diffusion pathway with an activation energy barrier height of 0.62 eV.
The directions perpendicular to the vacancy channels have higher energy
barriers for Oint diffusion. In addition, we have studied migration barriers
for oxygen vacancies that could be present as point defects within the
material. This in turn could also facilitate the transport of oxygen.
Interestingly, for oxygen vacancies, the lowest barrier height was found to
occur within the octahedral layer with an energy of 0.82 eV. Our results imply
that interstitial migration would be highly one-dimensional in nature. Oxygen
vacancy transport, on the other hand, could preferentially occur in the
two-dimensional octahedral plane.
