Oxygen diffusion pathways in brownmillerite SrCoO2.5: Influence of structure and chemical potential

TL;DR

This study uses first-principles calculations to reveal highly anisotropic oxygen diffusion pathways in brownmillerite SrCoO2.5, highlighting the role of structure and defects in ionic transport relevant for energy applications like SOFCs.

Contribution

It provides detailed insights into the anisotropic diffusion pathways and activation energies for oxygen interstitials and vacancies in SrCoO2.5 using first-principles methods.

Findings

Interstitial diffusion is highly one-dimensional along vacancy channels.

Oxygen vacancy migration occurs mainly within the octahedral layers.

Activation energy for interstitial diffusion is approximately 0.62 eV.

Abstract

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.