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Oxygen octahedral tilts underpin the functionality of a large number of perovskite-based materials and heterostructures with competing order parameters. We show how a precise analysis of atomic column shapes in Z-contrast scanning transmission electron microscopy images can reveal polarization and octahedral tilt behavior across uncharged and charged domain walls in BiFeO(3). This method is capable of visualizing octahedral tilts to much higher thicknesses than phase contrast imaging. We find that the octahedral tilt transition across a charged domain wall is atomically abrupt, while the associated polarization profile is diffuse (1.5-2 nm). Ginzburg-Landau theory then allows the relative contributions of polarization and the structural order parameters to the wall energy to be determined.

Abnormal behavior of supercooled liquid region in bulk-forming metallic glasses

The origin of the irreversible capacity of O3type NaFeO 2 charged to high voltage is investigated by analyzing the oxidation state of Fe and phase transition of layered NaFeO 2 cathodes for sodium-ion batteries during the charging process. In-situ X-ray absorption spectroscopy results revealed that charge compensation does not occur through the Fe 3+ /Fe 4+ redox reaction during sodium extraction as no significant shift to high energy was observed in the Fe K-edge. These results were reinforced with ex-situ near-edge X-ray absorption spectroscopy, which suggests that oxygen redox activity is responsible for charge compensation. Formation of Fe 3 O 4 product occurs because of oxygen release at high voltage when more than 0.5 Na is extracted from the structure; this is observed by transmission electron microscopy. NaFeO 2 irreversibility is due to the formation of Fe 3 O 4 with oxygen release, which inhibits Na insertion into the structure.