One-Dimensional Anti-Phase Structures Based on an Mg12Ce (Mn12Th-Type) Structure in an Mg91Ce6Zn3 Alloy, Studied by High-Resolution Transmission Electron Microscopy and High-Angle Annular Detector Dark-Field Scanning Transmission Electron Microscopy

The crystal structure of a new phase with an approximate composition of Mg91Ce7Zn2, which is formed as a main phase in an Mg91Ce6Zn3 alloy, has been determined by atomic-scale observations of high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). The structure of this phase can be described as a one-dimensional incommensurate structure with an orthorhombic unit cell of a=1.03 nm, b=1.03 nm and c= 3.7 nm, formed by insertion of anti-phase boundaries in the fundamental Mg12Ce (Mn12Th-type) structure with a tetragonal unit cell of a0=1.03 nm and c0=0.60 nm. The anti-phase boundaries are parallel to the (001) plane of the fundamental tetragonal structure, and an average interval of the boundaries along the [001] direction is about 3.1c0. Also, a commensurate structure with an interval of 5.5c0 is observed as a coexisting phase with the incommensurate structure.