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Dynamic and structural stability of cubic vanadium nitride

Mei, A. B. ; Hellman, O. ; Wireklint, N. ; Schlepütz, C. M. ; Sangiovanni, D. G. ; Alling, B. ; Rockett, A. ; Hultman, L. ; Petrov, I. ; Greene, J. E.

Physical review. B, Condensed matter and materials physics, 2015-02, Vol.91 (5), p.054101, Article 054101 [Periódico revisado por pares]

United States: American Physical Society

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  • Título:
    Dynamic and structural stability of cubic vanadium nitride
  • Autor: Mei, A. B. ; Hellman, O. ; Wireklint, N. ; Schlepütz, C. M. ; Sangiovanni, D. G. ; Alling, B. ; Rockett, A. ; Hultman, L. ; Petrov, I. ; Greene, J. E.
  • Assuntos: Anharmonicity ; Condensed matter ; Electrical resistivity ; Joining ; Molecular structure ; Phonons ; Reflection ; Transport ; X-ray diffraction
  • É parte de: Physical review. B, Condensed matter and materials physics, 2015-02, Vol.91 (5), p.054101, Article 054101
  • Notas: ObjectType-Article-1
    SourceType-Scholarly Journals-1
    ObjectType-Feature-2
    content type line 23
    AC02-06CH11357
    USDOE
  • Descrição: Structural phase transitions in epitaxial stoichiometric VN/MgO(011) thin films are investigated using temperature-dependent synchrotron x-ray diffraction (XRD), selected-area electron diffraction (SAED), resistivity measurements, high-resolution cross-sectional transmission electron microscopy, and ab initio molecular dynamics (AIMD). At room temperature, VN has the B1 NaCl structure. However, below T sub(c) = 250K, XRD and SAED results reveal forbidden (00l) reflections of mixed parity associated with a noncentrosymmetric tetragonal structure. The intensities of the forbidden reflections increase with decreasing temperature following the scaling behavior I [is proportional to] (T sub(c)-T) super(1/2). Resistivity measurements between 300 and 4 K consist of two linear regimes resulting from different electron/phonon coupling strengths in the cubic and tetragonal-VN phases. The VN transport Eliashberg spectral function alpha super(2) sub(tr) F ([Planck's over 2pi] omega ), the product of the phonon density of states F ([Planck's over 2pi] omega ) and the transport electron/phonon coupling strength alpha super(2) sub(tr) ([Planck's over 2pi] omega ), is determined and used in combination with AIMD renormalized phonon dispersion relations to show that anharmonic vibrations stabilize the NaCl structure at T > T sub(c). Free-energy contributions due to vibrational entropy, often neglected in theoretical modeling, are essential for understanding the room-temperature stability of NaCl-structure VN, and of strongly anharmonic systems in general.
  • Editor: United States: American Physical Society
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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