Indications of flat bands driving the δ to α volume collapse of plutonium

Journal Article · 13 February 2024 · Proceedings of the National Academy of Sciences of the United States of America

DOI: https://doi.org/10.1073/pnas.2308729121 · OSTI ID:2305438

Harrison, Neil  ^[1]; Chappell, Greta L. ^[2]; Tobash, Paul H. ^[3]

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1. MPA-MAGLAB, Los Alamos National Laboratory, Los Alamos, NM 87545
2. MPA-MAGLAB, Los Alamos National Laboratory, Los Alamos, NM 87545, MST-16, Los Alamos National Laboratory, Los Alamos, NM 87545
3. MST-16, Los Alamos National Laboratory, Los Alamos, NM 87545

On cooling from the melt, plutonium (Pu) undergoes a series of structural transformations accompanied by a ≈ 28% reduction in volume from its δ phase to its α phase at low temperatures. While Pu’s partially filled 5 f -electron shells are known to be involved, their precise role in the transformations has remained unclear. By using calorimetry measurements on α -Pu and gallium-stabilized δ -Pu combined with resonant ultrasound and X-ray scattering data to account for the anomalously large softening of the lattice with temperature, we show here that the difference in electronic entropy between the α and δ phases dominates over the difference in phonon entropy. Rather than finding an electronic specific heat characteristic of broad f -electron bands in α -Pu, as might be expected to occur within a Kondo collapsed phase in analogy with cerium, we find it to be indicative of flatter subbands. An important role played by Pu’s 5 f electrons in the formation of its larger unit cell α phase comprising inequivalent lattice sites and varying bond lengths is therefore suggested.

• Sponsoring Organization: USDOE
• OSTI ID: 2305438
• Alternate ID(s): OSTI ID: 2426726
• Journal Information: Proceedings of the National Academy of Sciences of the United States of America, Journal Name: Proceedings of the National Academy of Sciences of the United States of America Journal Issue: 8 Vol. 121; ISSN 0027-8424
• Publisher: Proceedings of the National Academy of SciencesCopyright Statement
• Country of Publication: United States
• Language: English