Identification of a bilayer grain boundary complexion in Bi-doped Cu

Using aberration-corrected scanning transmission electron microscopy, we have directly observed a bilayer grain boundary complexion in Bi-doped Cu, akin to that observed in Ni–Bi [Science, 333: 1730 (2011)]. In comparison with the Ni–Bi bilayer, the Cu–Bi bilayer appears to exist in a much narrower chemical potential window attributable to the fact that Cu–Bi and Ni–Bi have different pair-interaction potentials. Furthermore, these bilayers often form in conjunction with nanoscale faceting. This study demonstrates that direct imaging of the atom columns provides a more accurate understanding of the structure, chemistry and distribution of the adsorbates in a grain boundary and their role in embrittlement.