Computer simulation of the structure and dynamical properties of grain boundaries in a nanocrystalline model material

Molecular dynamics simulations have been used to synthesize and characterize a fully dense, three-dimensional nanocrystalline material with an average grain size of 43 Å by crystallization from the melt. The structures and energies of the highly constrained grain boundaries in this material are found to be more isotropic than those of extended boundaries in bicrystals. Based on this observation, a simple structural model that combines a realistic treatment of the grain boundaries with a finite grain size—and yet permits a comparison with the structures of unconstrained boundaries in bicrystals—is developed. The low temperature thermal behavior of such a model material is shown to be dominated by low frequency phonon modes due to the grain boundaries and grain junctions.