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Free energy and vibrational entropy difference between ordered and disordered Ni3Al

Ravelo, R. and Aguilar, J. and Baskes, M. and Angelo, J. E. and Fultz, B. and Holian, Brad Lee (1998) Free energy and vibrational entropy difference between ordered and disordered Ni3Al. Physical Review B, 57 (2). pp. 862-869. ISSN 0163-1829. http://resolver.caltech.edu/CaltechAUTHORS:RAVprb98

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Abstract

We have calculated free energy and vibrational entropy differences in Ni3Al between its equilibrium ordered structure and a disordered fcc solid solution. The free energy and entropy differences were calculated using the method of adiabatic switching in a molecular-dynamics formalism. The path chosen for the free-energy calculations directly connects the disordered with the ordered state. The atomic interactions are described by embedded-atom-method potentials. We find that the vibrational entropy difference increases with temperature from 0.14kB/atom at 300 K to 0.22kB/atom at 1200 K. We have calculated the density of states (DOS) of the disordered phase from the Fourier transform of the velocity-velocity autocorrelation function. The disordered DOS looks more like a broadened version of the ordered DOS. Analysis of the partial density of states shows that the Al atoms vibrations are most affected by the compositional disorder. The phonon partial spectral intensities along the 〈100〉 direction show that the vibrational spectrum of the disordered phase contains intensities at optical mode frequencies of the ordered alloy. We find that the volume difference between the ordered and disordered phases plays the most crucial role in the magnitude of the vibrational entropy difference. If the lattice constant of the two phases is set to the same value, the vibrational entropy difference decreases to zero.


Item Type:Article
Additional Information:©1998 The American Physical Society Received 17 October 1996; revised 15 May 1997 This work was supported by the U.S. Department of Energy under Contract No. DE-AC04-94AL85000. R.R. would like to thank Sandia National Laboratories, Livermore for their financial support during various stages of this work.
Record Number:CaltechAUTHORS:RAVprb98
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:RAVprb98
Alternative URL:http://dx.doi.org/10.1103/PhysRevB.57.862
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:1795
Collection:CaltechAUTHORS
Deposited By: Archive Administrator
Deposited On:18 Feb 2006
Last Modified:26 Dec 2012 08:46

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