PNNL

Abstract

We investigate the formation mechanisms of vacancy-ordered phase and collective mass transport in epitaxial SrCrO3-d films using ab initio simulations within the density functional theory formalism. We show that as concentration of oxygen vacancies (VO’s) increases, they form one-dimensional (1D) chains that feature Cr-centered tetrahedra. Aggregation of these 1D VO-chains results in the formation of (111)-oriented oxygen-deficient planes (VO-planes) and an extended vacancy-ordered phase observed in recent experiments. We discuss atomic scale mechanisms enabling the quasi-2D VO 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 SrCrO3-d at low-temperatures and provide insights into transient behavior necessary to harness ionic conductive oxides for high performance and low-temperature electrochemical reactors.