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Materials 2012, 5(6), 1040-1054; doi:10.3390/ma5061040
Article

Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description

1,* , 1,2
,
1
,
1
 and
1
1 Los Alamos National Laboratory, Los Alamos, NM 87545, USA 2 Jacobs School of Engineering, University of California, San Diego, La Jolla, CA 92093, USA
* Author to whom correspondence should be addressed.
Received: 11 April 2012 / Revised: 3 May 2012 / Accepted: 1 June 2012 / Published: 7 June 2012
(This article belongs to the Special Issue Negative Thermal Expansion Materials)
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Abstract

The δ phase of plutonium with the fcc structure exhibits an unusual negative thermal expansion (NTE) over its narrow temperature range of stability, 593–736 K. An accurate description of the anomalous high-temperature volume effect of plutonium goes beyond the current capability of electronic-structure calculations. We propose an atomistic scheme to model the thermodynamic properties of δ-Pu based on the two-state model of Weiss for the Invar alloys, inspired by the simple free-energy analysis previously conducted by Lawson et al. The two-state mechanism is incorporated into the atomistic description of a many-body interacting system. Two modified embedded atom method potentials are employed to represent the binding energies of two competing electronic states in δ-Pu. We demonstrate how the NTE takes place in δ-Pu by means of Monte Carlo simulations implemented with the two-state mechanism.
Keywords: plutonium; negative thermal expansion; Invar; Weiss model; modified embedded atom method; Monte Carlo method plutonium; negative thermal expansion; Invar; Weiss model; modified embedded atom method; Monte Carlo method
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).

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Lee, T.; Baskes, M.I.; Lawson, A.C.; Chen, S.P.; Valone, S.M. Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description. Materials 2012, 5, 1040-1054.

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