Synchrotron-Radiation-Based Photoelectron and X-Ray Absorption Spectroscopy of Cerium and Plutonium

摘要

The electronic structure of the actinides is of considerable interest as a result of the possibly correlated nature of the 5f electrons. At standard pressure, there is a profound difference between the early and late actinide metals, in the sense that the 5f electrons are delocalized (itinerant) for the elements up to and including α Pu, where they are localized and atomic-like for the elements beyond Pu. a similar trend has been reported in the lanthanides where the localization-delocalization transition takes place around the first element with an appreciable occupation of the 4f shell, Cerium. Cerium exhibits an alpha-gamma phase transition characterized by a volume expansion of 20%, which is analogous to the 26% volume expansion upon going from alpha to delta in Pu. Both cerium and plutonium exhibit similar physical properties, including multiple allotropic phases, and undergo large volume changes during transformation. This behavior has been hypothesized to be related to changes in the degree of localization of f-electrons in 4f electrons of Ce and 5f electrons of Pu. These properties make both Ce and Pu excellent candidate materials to study the variations of f-electronic behavior associated with phase changes. Additionally, Cerium is an ideal surrogate material for plutonium, considering that the study of Pu to this date has been compromised by its radioactivity properties and acute toxicity. Although the electronic structures of Ce and Pu have been investigated extensively, a complete understanding of their-f-electronic structure is still lacking.