Frase, H. and Fultz, B. and Robertson, J. L. (1998) Phonons in nanocrystalline Ni3Fe. Physical Review B, 57 (2). pp. 898-905. ISSN 0163-1829. http://resolver.caltech.edu/CaltechAUTHORS:FRAprb98
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Inelastic neutron-scattering spectra were measured to obtain the phonon density of states (DOS) of nanocrystalline fcc Ni3Fe. The materials were prepared by mechanical alloying, and were also subjected to heat treatments to alter their crystallite sizes and internal strains. In comparison to material with large crystallites, the nanocrystalline material shows two distinct differences in its phonon DOS. The nanocrystalline DOS was more than twice as large at energies below 15 meV. This increase was approximately proportional to the density of grain boundaries in the material. Second, features in the nanocrystalline DOS are broadened substantially. This broadening did not depend in a simple way on the crystallite size of the sample, suggesting that it has a different physical origin than the enhancement in phonon DOS at energies below 15 meV. A damped harmonic oscillator model for the phonons provides a quality factor Qu, as low as 7 for phonons in the nanocrystalline material. The difference in vibrational entropy of the bulk and nanocrystalline Ni3Fe was small, owing to competing changes in the nanocrystalline phonon DOS at low and high energies.
|Additional Information:||© 1998 The American Physical Society Received 2 September 1997 The Oak Ridge National Laboratory is managed for the Department of Energy by Lockheed Martin Energy Research, Oak Ridge, TN under Contract No. DE-AC05-96OR22464. This work was supported by the U.S. Department of Energy under Contract No. DE-FG03-96ER45572.|
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