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Dynamic and structural stability of cubic vanadium nitride
University of Illinois, IL 61801 USA; University of Illinois, IL 61801 USA.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology. CALTECH, CA 91125 USA.
Chalmers, Sweden.
Argonne National Lab, IL 60439 USA.
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2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 5, 054101- p.Article in journal (Refereed) Published
Abstract [en]

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-c = 250 K, 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 proportional to (T-c - T)(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 F-2(tr)(h omega), the product of the phonon density of states F(h omega) and the transport electron/phonon coupling strength alpha(2)(tr)(h omega), is determined and used in combination with AIMD renormalized phonon dispersion relations to show that anharmonic vibrations stabilize the NaCl structure at T greater than T-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.

Place, publisher, year, edition, pages
American Physical Society , 2015. Vol. 91, no 5, 054101- p.
National Category
Physical Sciences
URN: urn:nbn:se:liu:diva-114566DOI: 10.1103/PhysRevB.91.054101ISI: 000348872600001OAI: diva2:791634

Funding Agencies|Swedish Research Council (VR) program [637-2013-7296, 2014-5790, 2009-00971, 2013-4018]; Swedish Government Strategic Research Area Grant in Materials Science [SFO Mat-LiU 2009-00971]; DOE Office of Science by Argonne National Laboratory [DE-AC02-06CH11357]

Available from: 2015-03-02 Created: 2015-02-26 Last updated: 2016-08-31

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Hellman, OlleSangiovanni, DavideAlling, BjörnHultman, LarsPetrov, IvanGreene, Joseph E
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