Reversible nano-structuring of SrCrO3-δ through oxidation and reduction at low temperature

Oxygen vacancies are often present in complex oxides as point defects, and their effect on the electronic properties is typically uniform and isotropic. Exploiting oxygen deficiency in order to generate controllably novel structures and functional properties remains a challenging goal. Here we show that epitaxial strontium chromite films can be transformed, reversibly and at low temperature, from rhombohedral, semiconducting SrCrO2.8 to cubic, metallic perovskite SrCrO3-δ. Oxygen vacancies in SrCrO2.8 aggregate and give rise to ordered arrays of {111}-oriented SrO2 planes interleaved between layers of tetrahedrally coordinated Cr4+ and separated by ~1 nm. First-principle calculations provide insight into the origin of the stability of such nanostructures and, consistent with the experimental data, predict that the barrier for O2− diffusion along these quasi-two-dimensional nanostructures is significantly lower than that in cubic SrCrO3-δ. This property is of considerable relevance to solid oxide fuel cells in which fast O2− diffusion reduces the required operating temperature.