Small size atoms like hydrogen, nitrogen, oxygen, and carbon form interstitial in transition metals. The solubility of oxygen in Ti, Zr, and Hf is up to 33, 29, and 20 at. % In the octahedral interstitial sites respectively, at room temperature [1]. High solubility is attributed to the small distortion oxygen interstitials exert on these metals [2]. Similarly higher solubility of C in FCC Fe compared to BCC Fe is attributed to a small amount of strain exerted by C on Fe. But C and N interstitials prefer to be at the tetrahedral position compared to the octahedral position in metals like Pt [3]. Although the lattice parameter of Pt is much smaller than that of Ti, N prefers to occupy an octahedral position in Ti while it prefers to occupy a tetrahedral position in Pt. This observation is counterintuitive to the established notion that distortion plays a major role in the stability of interstitials. In this work, we explore the role of the distortion and electronic binding energy of Boron, oxygen, nitrogen, and carbon interstitials and their relative stability in the octahedral and tetrahedral, and substitutional sites. We also study the role of charge transfer from interstitial atoms to surrounding metals. We hope to show that in addition to distortion, charge transfer plays an important role in controlling the stability of interstitials.

 

[1] R.W. Cahn, P. Haasen, Physical Metallurgy, fourth ed., North-Holland Publishing Company, Amsterdam, 1996.

[2] A. v. Ruban, V.I. Baykov, B. Johansson, V. v. Dmitriev, M.S. Blanter, Oxygen and nitrogen interstitial ordering in hcp Ti, Zr, and Hf: An ab initio study, Phys Rev B 82 (2010) 134110.

[3] Xiaohui Hu, Torbjö rn Bjö rkman, Harri Lipsanen, Litao Sun, Arkady V. Krasheninnikov, “Solubility of Boron, Carbon, and Nitrogen in Transition Metals: Getting Insight into Trends from First-Principles Calculations” J. Phys. Chem. Lett. 6, 3263−3268, 2015.