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

• 成果类型: Article
• 署名作者: Harrison, Neil; Chappell, Greta L.; Tobash, Paul H.
• 署名单位: United States Department of Energy (DOE); Los Alamos National Laboratory; United States Department of Energy (DOE); Los Alamos National Laboratory
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-9571
• DOI: 10.1073/pnas.2308729121
• 发表日期: 2024-02-20
• 关键词: temperature heat-capacity; equation-of-state; chemical thermodynamics; electronic-structure; nuclear-materials; pu; TRANSITION; valence

摘要

On cooling from the melt, plutonium (Pu) undergoes a series of structural transformations accompanied by a approximate to 28% reduction in volume from its delta phase to its a phase at low temperatures. While Pu's partially filled 5f -electron shells are known to be involved, their precise role in the transformations has remained unclear. By using calorimetry measurements on a-Pu and gallium -stabilized delta-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 a and delta phases dominates over the difference in phonon entropy. Rather than finding an electronic specific heat characteristic of broad f -electron bands in a-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 5f electrons in the formation of its larger unit cell a phase comprising inequivalent lattice sites and varying bond lengths is therefore suggested.