On atomic structure of Guinier-Preston Zone in Mg-Zn-Gd alloy

The atomic structure of Guinier-Preston (G.P.) zone in an Mg-Zn-Gd alloy has been determined by combining atomic resolution high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) and first-principles calculation. The G.P. Zone consists of three atomic layers paralleling to (0001) plane of Mg matrix, where two outer layers enrich with Gd while the middle layer enriches with Zn. Moreover, it is found that most of the structures reported previously are unstable and should converge to the present result after atomic relaxation, even though the atomic species and positions in the middle layer vary in those models.