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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)
Download PDF [534 KB, 12 June 2012; original version 7 June 2012]

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 which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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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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