Isothermal aggregation of Bi atoms embedded in a soda borate glass: Coarsening of liquid nanodroplets and atomic diffusion

Abstract

The process of nucleation and growth of liquid Bi nanodroplets embedded in a soda borate glass submitted to isothermal annealing at different temperatures was studied by small-angle x-ray scattering (SAXS) and transmission-electron microscopy. The experimental results indicate that the formation and growth of Bi droplets occur in two successive stages after a short incubation period. The first is characterized by the nucleation and growth of spherical droplets promoted by atomic diffusion and aggregation of isolated Bi atoms and the second one by a subsequent droplet coarsening. The experimental functions describing the time variation of the droplet average radius and density number at advanced stages of the growth process agree with the classical Lifshitz-Slyozov-Wagner (LSW) theory. However, the radius distribution was demonstrated to be well described by a log-normal function thus differing from the prediction of the LSW model. The atomic diffusion coefficient of Bi was determined from SAXS results for several annealing temperatures and, from it, the activation energy for the diffusion process was inferred.