Theoretical study of metal borides stability

Aleksey N. Kolmogorov and Stefano Curtarolo
Phys. Rev. B 74, 224507 – Published 26 December 2006

Abstract

We have recently identified metal-sandwich (MS) crystal structures and shown with ab initio calculations that the MS lithium monoboride phases are favored over the known stoichiometric ones under hydrostatic pressure [Phys. Rev. B 73, 180501(R) (2006)]. According to previous studies synthesized lithium monoboride (LiBy) tends to be boron deficient (y=0.81.0), however, the mechanism leading to this phenomenon is not fully understood. We use a simple model to simulate this compound with ab initio methods and discover that the boron-deficient lithium monoboride is a remarkable adaptive binary alloy: it has virtually no energy barriers to change its composition post synthesis within a small but finite range of y at zero temperature. Having demonstrated that the model well explains the experimentally observed off-stoichiometry, we next compare the LiBy and MS-LiB phases and find that the latter have lower formation enthalpy under high pressures. We also systematically investigate the stability of MS phases for a large class of metal borides. Our results suggest that MS noble-metal borides are less unstable than the corresponding AlB2-type phases but not stable enough to form under equilibrium conditions.

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  • Received 25 July 2006

DOI:https://doi.org/10.1103/PhysRevB.74.224507

©2006 American Physical Society

Authors & Affiliations

Aleksey N. Kolmogorov and Stefano Curtarolo

  • Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27708, USA

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Issue

Vol. 74, Iss. 22 — 1 December 2006

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