Atomically Resolved Short-Range Order at the Nanoscale in the Ca-Mn-O System

The elucidation of the reaction mechanisms involving redox processes in functional transition-metal oxides, which usually start in areas of very few nanometers in size, is yet a challenge to be satisfactorily achieved. Atomically resolved HAADF and EELS have provided both chemical and structural information at the nanoscale, which reveal the preservation of short-range cationic order in areas of 2-3 nm length as the driving force behind the reversibility of the Ca₂Mn₃O₈-Ca₂Mn₃O₅ redox process. Oxygen evolution is accommodated by cationic diffusion along the Ca and Mn layers of the cation-deficient Ca₂Mn₃O₈ delafossite related structure, whereas Mn remains octahedrally coordinated.