First-principles study of bismuth films at transition-metal grain boundaries

Recent experiments suggest that Bi impurities segregate to form bilayer films on Ni and Cu grain boundaries (GBs) but do not segregate in Fe. To explain these phenomena, we study the total energies of Bi films on transition-metal (TM) Σ3(111) and Σ5(012) GBs using density functional theory. Our results agree with the observed stabilities. We propose a model to predict Bi bilayer stability at Ni GBs which suggests that Bi bilayer is not stable on (111) twist CSL GBs but is stable in most (100) twist CSL GBs. We investigate the interaction and bonding character between Bi and TMs to explain the differences among TMs based on localization of orbitals and magnetism, as well as evaluating the contribution of interfacial phonons at high temperature.