Temperature dependence of diffusion and structural defects in a molecular-dynamics model of amorphous Ni 81B 19

Abstract

The temperature dependence of atomic diffusion and the distribution of interatomic voids in Ni 81B 19 is studied by molecular-dynamics (MD) simulations, at temperatures less than and greater than the glass transition temperature. The voids can be classified according to the number of surrounding atoms and, for each class, the void volumes are log-normally distributed. This type of distribution is also observed in crystalline fcc Ni and Ni 3B models at room temperature. With increasing temperature, the number of larger voids increases, because of the thermal expansion and as a result of the coalescence of smaller voids. Voids with a volume larger than the activation volume for diffusion are considered to be defects. The defect concentration at room temperature is ≈10 −5 and shows an Arrhenian temperature dependence. This classification of the interatomic empty space leads to a plausible identification of sites in the structure that act as diffusion catalysts.