First-principles study of the diffusion of Li in bcc Fe

Abstract

First-principles calculations based on density functional theory were performed to investigate the diffusion behavior of lithium atoms in bcc iron crystals. The site-preference was verified primarily. The interactions with vacancies and self-interstitial atoms were analyzed. Subsequently, the diffusion mechanisms including migration path, energy barrier and diffusion coefficient were evaluated and discussed. The results show that the substitutional site is the favorite of lithium atoms since lithium atoms are even larger than iron atoms. Among all the interstitial sites, <111> dumbbell position has the lowest formation energy. The binding effects of substitutional lithium atoms for both vacancies and self-interstitial atoms were confirmed by our calculations. The high binding energy and low migration barrier for vacancies suggest the diffusion through vacancy mechanism is plausible. The reaction between a substitutional lithium atom and a self-interstitial atom will form a mixed <111> dumbbell eventually. The diffusion of interstitial lithium atoms is accomplished by the rotation of the <111> dumbbell, which has a very low energy barrier of 0.063 eV.