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Mass transport properties of quasiharmonic vs. anharmonic transition-metal nitrides
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Ruhr Univ Bochum, Germany.ORCID iD: 0000-0002-1379-6656
2019 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 688, article id 137297Article in journal (Refereed) Published
Abstract [en]

I present a development of the color-diffusion algorithm, used in non-equilibrium (accelerated) ab initio molecular dynamics simulations of point-defect migration in crystals [Sangiovanni et al., Phys. Rev. B 93, 094305 (2016)], to determine the temperature dependence of anion vacancy jump frequencies in rocksalt-structure (B1) TiN and VN characterized by quasiharmonic (TiN) vs. strongly anharmonic (VN) lattice dynamics. Over a temperature range [ 0.6"Tm amp;lt; T amp;lt; 0.9 T-m] relatively close to the materials melting points Tm, the simulations reveal that anion vacancy migration in TiN and VN exhibits an Arrhenius-like behavior, described by activation energies EJN = 4.2 0.3 eV and EZN = 3.1 0.3 eV, and attempt frequencies vTN = 8.1015 0.7 s-1 and vvN = 2.1017 c).8s-1. A comparison of activation energies E extracted by Arrhenius linear regression at elevated temperatures with ab initio E,,ca values calculated at 0 Kelvin reveals that, while the nitrogen migration energy amp;ills varies modestly with temperature {AEPN = [E-a(T-m)- Ea(0 K)1/Ea(0 K) 0.1}, the changes in EavN vs. T are considerable (AEavN 1). The temperature-induced variations in vacancy migration energies and diffusivities are discussed in relation to the TiN and VN vibrational properties determined via ab initio molecular dynamics at different temperatures. It is argued that static 0-K calculations, which account for thermal expansion effects within the framework of quasiharmonic transition-state theory, accurately reproduce the finite-temperature mass transport properties of TiN. Conversely, the use of molecular dynamics simulations, which explicit treat lattice vibrations at any temperature of interest, is necessary to achieve reliable atomic diffusivities in B1 VN, a crystal phase dynamically stabilized by anharmonic vibrations [Mei et al., Phys. Rev. B 91, 054101 (2015)].

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA , 2019. Vol. 688, article id 137297
Keywords [en]
Nitrides; Diffusion; Ab initio; Molecular dynamics; Vacancies; Lattice dynamics; Anharmonicity; Transition-state theory
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-160975DOI: 10.1016/j.tsf.2019.05.016ISI: 000485256500027OAI: oai:DiVA.org:liu-160975DiVA, id: diva2:1370230
Note

Funding Agencies|Olle Engkvist Foundation; VINN Excellence Center Functional Nanoscale Materials (FunMat-2) [2016-05156]

Available from: 2019-11-14 Created: 2019-11-14 Last updated: 2020-01-13

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The full text will be freely available from 2021-05-08 11:27
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