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Thermodynamic stability and contributions to the Gibbs free energy of nanocrystalline Ni₃Fe

Lohaus, Stefan H. and Johnson, Michel B. and Ahnn, Peter F. and Saunders, Claire N. and Smith, Hillary L. and White, Mary Anne and Fultz, Brent (2020) Thermodynamic stability and contributions to the Gibbs free energy of nanocrystalline Ni₃Fe. Physical Review Materials, 4 (8). Art. No. 086002. ISSN 2475-9953.

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The heat capacities of nanocrystalline Ni₃Fe and control materials with larger crystallites were measured from 0.4–300 K. The heat capacities were integrated to obtain the enthalpy, entropy, and Gibbs free energy and to quantify how these thermodynamic functions are altered by nanocrystallinity. From the phonon density of states (DOS) measured by inelastic neutron scattering, we find that the Gibbs free energy is dominated by phonons and that the larger heat capacity of the nanomaterial below 100 K is attributable to its enhanced phonon DOS at low energies. Besides electronic and magnetic contributions, the nanocrystalline material has an additional contribution at higher temperatures, consistent with phonon anharmonicity. The nanocrystalline material shows a stronger increase with temperature of both the enthalpy and entropy compared to the bulk sample. Its entropy exceeds that of the bulk material by 0.4 k_B/atom at 300 K. This is insufficient to overcome the enthalpy of grain boundaries and defects in the nanocrystalline material, making it thermodynamically unstable with respect to the bulk control material.

Item Type:Article
Related URLs:
URLURL TypeDescription
Lohaus, Stefan H.0000-0002-4430-3834
Saunders, Claire N.0000-0001-7973-3722
White, Mary Anne0000-0001-8142-0004
Fultz, Brent0000-0002-6364-8782
Alternate Title:Thermodynamic stability and contributions to the Gibbs free energy of nanocrystalline Ni3Fe
Additional Information:© 2020 American Physical Society. (Received 11 September 2019; revised 10 January 2020; accepted 21 July 2020; published 11 August 2020) This work was supported by the Department of Energy through the Office of Science, Basic Energy Sciences Grant DE-FG02-03ER46055. M.A.W. acknowledges support from the Natural Sciences and Engineering Research Council of Canada (Grant No. RGPIN-2015-04593), the Canada Foundation for Innovation, and the Clean Technologies Research Institute at Dalhousie University.
Funding AgencyGrant Number
Department of Energy (DOE)DE-FG02-03ER46055
Natural Sciences and Engineering Research Council of Canada (NSERC)RGPIN-2015-04593
Canada Foundation for InnovationUNSPECIFIED
Dalhousie UniversityUNSPECIFIED
Issue or Number:8
Record Number:CaltechAUTHORS:20200811-114716456
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104908
Deposited By: George Porter
Deposited On:11 Aug 2020 19:26
Last Modified:11 Aug 2020 19:26

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