One-Dimensional Anti-Phase Structures Based on an Mg<SUB>12</SUB>Ce (Mn<SUB>12</SUB>Th-Type) Structure in an Mg<SUB>91</SUB>Ce<SUB>6</SUB>Zn<SUB>3</SUB> Alloy, Studied by High-Resolution Transmission Electron Microscopy and High-Angle Annular Detector Dark-Field Scanning Transmission Electron Microscopy

Abstract

The crystal structure of a new phase with an approximate composition of Mg 91 Ce 7 Zn 2 , which is formed as a main phase in an Mg 91 Ce 6 Zn 3 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 Mg 12 Ce (Mn 12 Th-type) structure with a tetragonal unit cell of a 0 = 1.03 nm and c 0 = 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 3.1c 0 . Also, a commensurate structure with an interval of 5.5c 0 is observed as a coexisting phase with the incommensurate structure.