Sedimentation process for atoms in a Bi-Sb system alloy under a strong gravitational field: a new type of diffusion of substitutional solutes

Abstract

Abstract An atomic-scale graded structure had been formed by the sedimentation of substitutional solute atoms in a 70 mol∼ Bi-30 mol∼ Sb alloy under a strong gravitational field of over 106 g level at maximum acceleration according to previous work of Mashimo et al. In this study, a simulation of the sedimentation process in the Bi-Sb alloy was performed using a self-consistent theory to discuss the diffusion mechanism. The simulation was performed first in an infinite radius range to confirm the validity of the simulation program. We simulated the sedimentation process in a finite radius range by changing the ratio between the diffusion coefficients for sedimentation and the internal chemical potential for comparison with the experimental results. The simulation result suggested that the diffusion coefficient for sedimentation was very large compared with that for conventional diffusion, even though substitutional solutes acted in this system. This indicated that the diffusion mechanism for sedimentation was different from the vacancy mechanism.