Atomic Size Effect in Impurity Induced Grain Boundary Embrittlement

Bismuth segregated to the grain boundary in Cu is known to promote brittle fracture of this material. Schweinfest et al. [Nature 432 (2004) 1008-1011] reported first-principles quantum mechanical calculations on the electronic and structural properties of a Cu grain boundary with and without segregated Bi and argue that the grain boundary weakening induced by Bi is a simple atomic size effect. But their conclusion is incomplete for both Bi and Pb because it fails to distinguish the chemical and mechanical (atomic size) contributions, as obtained with our recently developed first-principles based phenomenological theory.