Low-Dimensional Oxygen Vacancy Ordering and Diffusion in SrCrO_3-δ

We investigate the formation mechanisms of vacancy-ordered phase and collective mass transport in epitaxial SrCrO_3-δ films using ab initio simulations within the density functional theory formalism. We show that as the concentration of oxygen vacancies (V_O) increases, they form 1D chains that feature Cr-centered tetrahedra. Aggregation of these 1D V_O chains results in the formation of (111)-oriented oxygen-deficient planes and an extended vacancy-ordered phase observed in recent experiments. We discuss atomic-scale mechanisms enabling the quasi-2D V_O aggregates to expand along and translate across (111) planes. The corresponding lowest activation energy pathways necessarily involve rotation of Cr-centered tetrahedra, which emerges as a universal feature of fast ionic conduction in complex oxides. These findings explain reversible oxidation and reduction in SrCrO_3-δ at low temperatures and provide insights into transient behavior necessary to harness ionic conductive oxides for high-performance and low-temperature electrochemical reactors.