First-principles phase stability in the Ti-V alloy system

[摘要] Phase stability in the transition metals are mostly dictated by the bonding of the d electrons and is believed to be fairly well understood from either a canonical-band picture or a tight-binding model. These models are related and capture the fact that as one proceeds through the nonmagnetic d-transition series one encounters the hexagonal close-packed (hcp), body-centered cubic (bcc), hcp, and face-centered cubic (fcc) phases. This structural sequence depends on the gradual filling of the d band (roughly one electron per atomic number increase) that is altered when magnetism is present simply due to the spin polarization of the d band. However, recent more careful experimental and theoretical studies have shown that the aforementioned appealing models do not entirely explain the bonding and phase stability in the transition metals. First, there is a destabilization of the bcc phase due to pressure in the Group Vb metals (V, Nb, and Ta) and second, a temperature-induced stabilization of the bcc phase in the Group IVb (Ti, Zr, and Hf) metals even though at low temperatures it is strongly unstable. Here we address the latter phenomenon and study the influence of alloying titanium with its next neighbor vanadium by applying the recently developed self-consistent ab initio lattice dynamics (SCAILD) approach that has heretofore never been utilized for an alloy system. (C) 2013 Elsevier B.V. All rights reserved.

[发布日期] 2013-12-25

[关键词] Transition metals;Phase stability;Alloys;Phonons;Density-functional theory