Direct Atomic Observation in Powdered 4H-Ba0.8Sr0.2Mn0.4Fe0.6O2.7

A new hexagonal polytype in the BaMn1‑x Fe x O3‑δ system has been stabilized. Powdered Ba0.8Sr0.2MnIV 0.4FeIII 0.6O2.70 crystallizes in the 4H hexagonal polytype (space group P63/mmc) according to X-ray diffraction. HAADF images and chemical maps with atomic resolution have been obtained by combining Cs-corrected electron microscopy and EELS spectroscopy. The structure is formed by dimers of face-sharing octahedra linked by corners. EELS data show a random distribution of the transition metals ions identified by Fe and Mn-L2,3 chemical maps. A systematic difference in contrast observed in the O–K signal mapping suggests that anion deficiency is randomly located along the hexagonal layers in agreement with ND data. The magnetic structure consists of ferromagnetic sheets with the magnetic moments aligned along the x-axis and coupled antiferromagnetically along the c-axis.