Fig. 1. Schematic illustration of a PB, a GB, and a CB.

(A) PB, a boundary between two grains of different lattice type. (B) GB, a boundary between two grains of the same lattice type but with different crystallographic orientations. (C) CB, defined by a sharp discontinuity of at least one elemental concentration inside a lattice-continuous region, e.g., a very sharp chemical gradient. Note that our CBs do not involve any change in crystal structure or lattice orientation. The different colors represent atoms of different element type.