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Nonharmonic phonons in α-iron at high temperatures

Mauger, L. and Lucas, M. S. and Muñoz, J. A. and Tracy, S. J. and Kresch, M. and Xiao, Yuming and Chow, Paul and Fultz, B. (2014) Nonharmonic phonons in α-iron at high temperatures. Physical Review B, 90 (6). Art. No. 064303. ISSN 1098-0121. https://resolver.caltech.edu/CaltechAUTHORS:20141121-135832086

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Abstract

Phonon densities of states (DOS) of bcc α−^(57)Fe were measured from room temperature through the 1044 K Curie transition and the 1185 K fcc γ-Fe phase transition using nuclear resonant inelastic x-ray scattering. At higher temperatures all phonons shift to lower energies (soften) with thermal expansion, but the low transverse modes soften especially rapidly above 700 K, showing strongly nonharmonic behavior that persists through the magnetic transition. Interatomic force constants for the bcc phase were obtained by iteratively fitting a Born–von Kármán model to the experimental phonon spectra using a genetic algorithm optimization. The second-nearest-neighbor fitted axial force constants weakened significantly at elevated temperatures. An unusually large nonharmonic behavior is reported, which increases the vibrational entropy and accounts for a contribution of 35 meV/atom in the free energy at high temperatures. The nonharmonic contribution to the vibrational entropy follows the thermal trend of the magnetic entropy, and may be coupled to magnetic excitations. A small change in vibrational entropy across the α−γ structural phase transformation is also reported.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.064303PublisherArticle
http://dx.doi.org/10.1103/PhysRevB.90.064303DOIArticle
http://arxiv.org/abs/1404.4998arXivDiscussion Paper
http://journals.aps.org/prb/abstract/10.1103/PhysRevB.90.064303#supplementalPublisherSupplemental Material
ORCID:
AuthorORCID
Fultz, B.0000-0002-6364-8782
Additional Information:© 2014 American Physical Society. Published 20 August 2014. Received 19 April 2014. Revised 7 July 2014. This work benefited from important discussions with Drs. W. Sturhahn, F. Körmann, B. Grabowski, T. Hickel, and J. Neugebauer. This work was supported by the Department of Energy through the Carnegie-DOE Alliance Center, funded by the Department of Energy through the Stewardship Sciences Academic Alliance Program. This work benefited from DANSE software developed under NSF Grant No.DMR-0520547. Portions of this work were performed at HPCAT (Sector 16),Advanced Photon Source (APS),Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA under Award No. DE-NA0001974 and DOEBES under Award No. DE-FG02-99ER45775, with partial instrumentation funding by NSF. The Advanced Photon Source is a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DEAC02-06CH11357.
Funders:
Funding AgencyGrant Number
Carnegie-DOE Alliance CenterUNSPECIFIED
Department of Energy (DOE) National Nuclear Security AdministrationUNSPECIFIED
NSFDMR-0520547
Department of Energy (DOE)DE-NA0001974
Department of Energy (DOE)DE-FG02-99ER45775
Department of Energy (DOE)DE-AC02-06CH11357
Issue or Number:6
Classification Code:PACS: 63.20.dd, 65.40.gd, 75.50.Bb, 63.20.kk
Record Number:CaltechAUTHORS:20141121-135832086
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20141121-135832086
Official Citation:Nonharmonic phonons in α-iron at high temperatures Mauger, L. and Lucas, M. S. and Muñoz, J. A. and Tracy, S. J. and Kresch, M. and Xiao, Yuming and Chow, Paul and Fultz, B., Phys. Rev. B, V.90, no.6, pages 064303, 2014 American Physical Society, (10.1103/PhysRevB.90.064303), {http://link.aps.org/doi/10.1103/PhysRevB.90.064303}
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52052
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:21 Nov 2014 22:36
Last Modified:03 Oct 2019 07:38

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