Plutonium metallurgy lies at the heart of science-based stockpile stewardship. One aspect is concerned with developing predictive capabilities to describe the properties of stockpile materials, including an assessment of microstructural changes with age. Yet, the complex behavior of plutonium, which results from the competition of its 5f electrons between a localized (atomic-like or bound) state and an itinerant (delocalized bonding) state, has been challenging materials scientists and physicists for the better part of five decades. Although far from quantitatively absolute, electronic-structure theory provides a description of plutonium that helps explain the unusual properties of plutonium, as recently reviewed by Hecker. (See also the article by Hecker in this issue.) The electronic structure of plutonium includes five 5f electrons with a very narrow energy width of the 5f conduction band, which results in a delicate balance between itinerant electrons (in the conduction band) or localized electrons and multiple lowenergy electronic configurations with nearly equivalent energies. These complex electronic characteristics give rise to unique macroscopic properties of plutonium that include six allotropes (at ambient pressure) with very close free energies but large (∼25%) density differences, a lowsymmetry monoclinic ground state rather than a high-symmetry close-packed cubic phase, compression upon melting (like water), low melting temperature, anomalous temperature-dependence of electrical resistance, and radioactive decay. Additionally, plutonium readily oxidizes and is toxic; therefore, the handling and fundamental research of this element is very challenging due to environmental, safety, and health concerns.
钚冶金学是基于科学的弹药储备管理的核心。其中一个方面是关注于开发预测能力,以描述弹药储备材料的特性,包括评估随时间变化的微观结构变化。然而,钚的复杂行为源于其5个f电子在局部(类原子或束缚)状态和漫游(分散键合)状态之间的竞争,这已经挑战了材料科学家和物理学家近五十年。虽然远非定量绝对,但电子结构理论提供了对钚的描述,有助于解释钚的异常特性,正如Hecker最近所述。 (请参阅本期Hecker的文章。)钚的电子结构包括五个5f电子,具有非常窄的5f导带能量宽度,这导致漫游电子(在导带中)或局部电子之间的微妙平衡,以及多个低能量电子构型的几乎等效能量。这些复杂的电子特性导致钚的独特宏观特性,包括六种同素异形体(在常压下)具有非常接近的自由能,但密度差异很大(约25%),低对称单斜晶态而不是高对称的紧密堆积立方相,熔化时的压缩(像水),低熔点,电阻的异常温度依赖性和放射性衰变。此外,钚容易氧化并具有毒性;因此,由于环境、安全和健康方面的考虑,处理和基础研究这种元素是非常具有挑战性的。