Atomic-scale graded structure formed by sedimentation of substitutional atoms in a Bi–Sb alloy

An atomic-scale graded structure was formed by the sedimentation of component atoms in an all-proportional miscible alloy under a strong gravitational field of 1 million g in maximum acceleration at high temperature. Continuous composition gradients of Sb (about 20–0 wt. %) and Bi (about 80–100 wt. %) and the resultant continuous change in the lattice constants were observed in the ultracentrifuged Bi–Sb (70:30 in mol %) alloy bulk body. Crystal growth in the direction of acceleration field was also observed. It must be noted that the substitutional solute atoms with component level rate acted in the sedimentation of this system, while interstitial solutes (Au) at an impurity level rate acted in some elemental metals with low melting temperature in the previous studies. It is expected that the sedimentation of substitutional atoms can be used to control the compositions and structure of alloys or compounds.