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Cluster expansion Monte Carlo study of phase stability of vanadium nitrides

Ravi, C. and Sahu, H. K. and Valsakumar, M. C. and van de Walle, Axel (2010) Cluster expansion Monte Carlo study of phase stability of vanadium nitrides. Physical Review B, 81 (10). Art. No. 104111. ISSN 1098-0121.

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Phase stability of stable and metastable vanadium nitrides is studied using density functional theory (DFT) based total-energy calculations combined with cluster expansion Monte Carlo simulation and supercell methods. We have computed the formation enthalpy of the various stable and metastable vanadium nitride phases considering the available structural models and found that the formation enthalpies of the different phases decrease in the same order as they appear in the experimental aging sequence. DFT calculations are known to show stoichiometric V2N to be polymorphic in ϵ-Fe_2N and ζ-Fe2_N structures within a few meV and VN to be more stable in WC(B_h) phase than in the experimentally observed NaCl(B1) structure. As these nitrides are known to be generally nonstoichiometric due to presence of nitrogen vacancies, we used cluster expansion and supercell methods for examining the effect of nitrogen vacancies on the phase stability. It is found that nitrogen vacancies, represented by ◻, stabilize ϵ-Fe_2N phase of V_2N_(1−x◻x) and NaCl(B1) phase of VN_(1−x◻x) compared to ζ-Fe_2N and WC(B_h) phases respectively, rendering the computed phase stability scenario to be in agreement with experiments. Analysis of supercell calculated electronic density of states (DOS) of VN_(1−x◻x) with varying x, shows that the nitrogen vacancies increase the DOS at Fermi level in WC phase, whereas they decrease the DOS in NaCl phase. And this serves as the mechanism of enhancement of the stability of the NaCl phase. Monte Carlo simulations were used for computing the finite temperature formation enthalpies of these phases as a function of nitrogen-vacancy concentration and found close agreement for NaCl(B1) phase of VN_(1−x◻x) for which measured values are available.

Item Type:Article
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van de Walle, Axel0000-0002-3415-1494
Additional Information:© 2010 The American Physical Society. Received 27 November 2009; revised 27 January 2010; published 18 March 2010. One of the authors, C. Ravi, thanks B. K. Panigrahi for the discussion and support for the work. Axel van de Walle acknowledges that this research was supported by the U.S. National Science Foundation through TeraGrid resources provided by NCSA under Grant No. DMR050013N, through the U.S. Department of Energy, National Energy Research Initiative Consortium (NERI-C) under Grant No. DE-FG07- 07ID14893.
Funding AgencyGrant Number
National Center for Supercomputing Applications (NCSA)DMR050013N
U. S. Department of Energy, National Energy Research Initiative Consortium (NERI-C)DE-FG0707ID14893
Issue or Number:10
Classification Code:PACS: 61.50.Lt, 64.75.Ef, 71.20.Be
Record Number:CaltechAUTHORS:20100611-141703456
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18654
Deposited By: Tony Diaz
Deposited On:13 Jun 2010 04:22
Last Modified:09 Mar 2020 13:19

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