Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 117, Issue 9, Pages 4480-4485Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1918281117
Keywords
plutonium; bulk modulus; softening; electronic configurations
Categories
Funding
- Los Alamos National Laboratory Laboratory Directed Research and Development (LDRD) program [20180025DR]
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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 Gruneisen 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 delta 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.
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