title: Direct imaging of layered O3- and P2-NaxFe1/2Mn1/2O2 structures at the atomic scale.
abstract: Using aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques, the atomic-scale structures of the O3 and P2 phases of NaxFe1/2Mn1/2O2 are investigated systematically. The Na, transition metal M (Fe and Mn) and O columns are well revealed and precisely assigned to the O3 and P2 phase layered structures. The O3 phase sample demonstrates larger atomic site fluctuations along [001] direction but with less structural imperfections (e.g. interlayer structure and stacking defaults) than the P2 phase sample. Furthermore, a clear surface with a regular structure is observed for the O3-NaFe1/2Mn1/2O2 sample, while a surface with a large amount of Na-M antisites is observed for the P2-Na2/3Fe1/2Mn1/2O2 sample.
authors.affiliation: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing, 100190, China. yshu@aphy.iphy.ac.cn l.gu@iphy.ac.cn.
authors.forename: Xia
authors.initials: X
authors.lastname: Lu
authors.forename: Yuesheng
authors.initials: Y
authors.lastname: Wang
authors.forename: Pin
authors.initials: P
authors.lastname: Liu
authors.forename: Lin
authors.initials: L
authors.lastname: Gu
authors.forename: Yong-Sheng
authors.initials: YS
authors.lastname: Hu
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.forename: George P
authors.initials: GP
authors.lastname: Demopoulos
authors.forename: Liquan
authors.initials: L
authors.lastname: Chen