Lucas, M. S. and Muñoz, J. A. and Mauger, L. and Li, Chen W. and Sheets, A. O. and Turgut, Z. and Horwath, J. and Abernathy, D. L. and Stone, M. B. and Delaire, O. and Xiao, Yuming and Fultz, B. (2010) Effects of chemical composition and B2 order on phonons in bcc Fe–Co alloys. Journal of Applied Physics, 108 (2). Art. No. 023519 . ISSN 0021-8979 http://resolver.caltech.edu/CaltechAUTHORS:20100831-094242871
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The phonon density of states (DOS) gives insight into interatomic forces and provides the vibrational entropy, making it a key thermodynamic function for understanding alloy phase transformations. Nuclear resonant inelastic x-ray scattering and inelastic neutron scattering were used to measure the chemical dependence of the DOS of bcc Fe–Co alloys. For the equiatomic alloy, the A2→B2 (chemically disordered→chemically ordered) phase transformation caused measurable changes in the phonon spectrum. The measured change in vibrational entropy upon ordering was −0.02±0.02 k_B/atom, suggesting that vibrational entropy results in a reduction in the order–disorder transition temperature by 60±60 K. The Connolly–Williams cluster inversion method was used to obtain interaction DOS (IDOS) curves that show how point and pair variables altered the phonon DOS of disordered bcc Fe–Co alloys. These IDOS curves accurately captured the change in the phonon DOS and vibrational entropy of the B2 ordering transition.
|Additional Information:||© 2010 American Institute of Physics. Received 5 April 2010; accepted 24 May 2010; published online 29 July 2010; corrected 6 August 2010. The portions of this work conducted at Oak Ridge National Laboratory were supported by the Scientific User Facilities Division and by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, DOE. This work was supported by the Department of Energy through the Basic Energy Sciences Grant Nos. DE-FG02- 03ER46055 and BES-MS, W-31-109-ENG-38. Portions of this work were performed at HPCAT (Sector 16), Advanced Photon Source (APS), Argonne National Laboratory. Use of the HPCAT facility was supported by DOE-BES, DOENNSA (CDAC), NSF, DOD–TACOM, and the W. M. Keck Foundation. Use of the APS was supported by DOE-BES under Contract No. DE-AC02-06CH11357. This work benefited from DANSE software developed under NSF Grant No. DMR-0520547.|
|Subject Keywords:||cobalt alloys, entropy, ferromagnetic materials, iron alloys, nuclear chemical analysis, order-disorder transformations, phonon-phonon interactions, X-ray scattering|
|Classification Code:||PACS: 81.30.Hd; 64.70.K-; 63.20.kg; 65.40.gd; 78.70.Ck; 82.80.-d|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||01 Sep 2010 20:47|
|Last Modified:||26 Dec 2012 12:22|
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