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Title: Electronically driven collapse of the bulk modulus in δ -plutonium

Abstract

Plutonium metal exhibits an anomalously large softening of its bulk modulus at elevated temperatures that is made all the more extraordinary by the finding that it occurs irrespective of whether the thermal expansion coefficient is positive, negative, or zero—representing an extreme departure from conventional Grüneisen scaling. We show here that the cause of this softening is the compressibility of plutonium’s thermally excited electronic configurations, which has thus far not been considered in thermodynamic models. We show that when compressible electronic configurations are thermally activated, they invariably give rise to a softening of the bulk modulus regardless of the sign of their contribution to the thermal expansion. The electronically driven softening of the bulk modulus is shown to be in good agreement with elastic moduli measurements performed on the gallium-stabilized δ phase of plutonium over a range of temperatures and compositions and is shown to grow rapidly at small concentrations of gallium and at high temperatures, where it becomes extremely sensitive to hydrostatic pressure.

Authors:
ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1616427
Report Number(s):
LA-UR-19-32035
Journal ID: ISSN 0027-8424
Grant/Contract Number:  
89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
Proceedings of the National Academy of Sciences of the United States of America
Additional Journal Information:
Journal Volume: 117; Journal Issue: 9; Journal ID: ISSN 0027-8424
Publisher:
National Academy of Sciences
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; plutonium; bulk modulus; softening; electronic configurations

Citation Formats

Harrison, Neil. Electronically driven collapse of the bulk modulus in δ -plutonium. United States: N. p., 2020. Web. doi:10.1073/pnas.1918281117.
Harrison, Neil. Electronically driven collapse of the bulk modulus in δ -plutonium. United States. doi:https://doi.org/10.1073/pnas.1918281117
Harrison, Neil. Tue . "Electronically driven collapse of the bulk modulus in δ -plutonium". United States. doi:https://doi.org/10.1073/pnas.1918281117. https://www.osti.gov/servlets/purl/1616427.
@article{osti_1616427,
title = {Electronically driven collapse of the bulk modulus in δ -plutonium},
author = {Harrison, Neil},
abstractNote = {Plutonium metal exhibits an anomalously large softening of its bulk modulus at elevated temperatures that is made all the more extraordinary by the finding that it occurs irrespective of whether the thermal expansion coefficient is positive, negative, or zero—representing an extreme departure from conventional Grüneisen scaling. We show here that the cause of this softening is the compressibility of plutonium’s thermally excited electronic configurations, which has thus far not been considered in thermodynamic models. We show that when compressible electronic configurations are thermally activated, they invariably give rise to a softening of the bulk modulus regardless of the sign of their contribution to the thermal expansion. The electronically driven softening of the bulk modulus is shown to be in good agreement with elastic moduli measurements performed on the gallium-stabilized δ phase of plutonium over a range of temperatures and compositions and is shown to grow rapidly at small concentrations of gallium and at high temperatures, where it becomes extremely sensitive to hydrostatic pressure.},
doi = {10.1073/pnas.1918281117},
journal = {Proceedings of the National Academy of Sciences of the United States of America},
number = 9,
volume = 117,
place = {United States},
year = {2020},
month = {2}
}

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