Publication detail
Point defects stabilise cubic Mo-N and Ta-N
KOUTNÁ, N. HOLEC, D. SVOBODA, O. KLIMASHIN, F. MAYRHOFER, P.
English title
Point defects stabilise cubic Mo-N and Ta-N
Type
journal article in Web of Science
Language
en
Original abstract
We employab initio calculations to investigate energetics of point defects in metastable rocksalt cubic Ta-N and Mo-N. Our results reveal a strong tendency to off-stoichiometry, i.e. defected structures are predicted to be more stable than perfect ones with 1:1 metal-to-nitrogen stoichiometry, in agreement with previous literature reports. While Ta-N significantly favours metal vacancies, Mo-N exhibits similar energies of formation regardless of the vacancy type (V Mo , V N ) as long as their concentration is below ?15at.\% . The overall lowest energy of formation were obtained for Ta 0.78 N and Mo 0.91 N , which are hence predicted to be the most stable compositions. To account for various experimental condition during synthesis, we further evaluated the phase stability as a function of chemical potential of individual species. The proposed phase diagrams reveal four stable compositions, Mo 0.84 N , Mo 0.91 N , MoN 0.69 and MoN 0.44 , in the case of Mo-N and nine stable compositions in the case of Ta-N indicating the crucial role of metal under-stoichiometry, since Ta 0.75 N and Ta 0.78 N significantly dominate the diagram. These results are important for understanding and designing experiments using non-equilibrium deposition techniques. Finally, we discuss a role of defects ordering and estimate a cubic lattice parameter as a function of a defect contents.
English abstract
We employab initio calculations to investigate energetics of point defects in metastable rocksalt cubic Ta-N and Mo-N. Our results reveal a strong tendency to off-stoichiometry, i.e. defected structures are predicted to be more stable than perfect ones with 1:1 metal-to-nitrogen stoichiometry, in agreement with previous literature reports. While Ta-N significantly favours metal vacancies, Mo-N exhibits similar energies of formation regardless of the vacancy type (V Mo , V N ) as long as their concentration is below ?15at.\% . The overall lowest energy of formation were obtained for Ta 0.78 N and Mo 0.91 N , which are hence predicted to be the most stable compositions. To account for various experimental condition during synthesis, we further evaluated the phase stability as a function of chemical potential of individual species. The proposed phase diagrams reveal four stable compositions, Mo 0.84 N , Mo 0.91 N , MoN 0.69 and MoN 0.44 , in the case of Mo-N and nine stable compositions in the case of Ta-N indicating the crucial role of metal under-stoichiometry, since Ta 0.75 N and Ta 0.78 N significantly dominate the diagram. These results are important for understanding and designing experiments using non-equilibrium deposition techniques. Finally, we discuss a role of defects ordering and estimate a cubic lattice parameter as a function of a defect contents.
Keywords in English
Mo-N;Ta-N;point defects;vacancies;stability;DFT
Released
22.08.2016
Publisher
IOP PUBLISHING LTD
Location
TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND
ISSN
0022-3727
Volume
49
Number
37
Pages from–to
1–8
Pages count
8
BIBTEX
@article{BUT127123,
author="Nikola {Koutná} and David {Holec} and Ondřej {Svoboda} and Fedor {Klimashin} and Paul {Mayrhofer},
title="Point defects stabilise cubic Mo-N and Ta-N",
year="2016",
volume="49",
number="37",
month="August",
pages="1--8",
publisher="IOP PUBLISHING LTD",
address="TEMPLE CIRCUS, TEMPLE WAY, BRISTOL BS1 6BE, ENGLAND",
issn="0022-3727"
}