The ground-state electronic structures of the actinide oxides $A\text{O}$, ${A}_{2}{\text{O}}_{3}$, and $A{\text{O}}_{2}$ ($A=\text{U}$, Np, Pu, Am, Cm, Bk, and Cf) are determined from first-principles calculations, using the self-interaction corrected local spin-density approximation. Emphasis is put on the degree of $f$-electron localization, which for $A{\text{O}}_{2}$ and ${A}_{2}{\text{O}}_{3}$ is found to follow the stoichiometry, namely, corresponding to ${A}^{4+}$ ions in the dioxide and ${A}^{3+}$ ions in the sesquioxides. In contrast, the ${A}^{2+}$ ionic configuration is not favorable in the monoxides, which therefore become metallic. The energetics of the oxidation and reduction in the actinide dioxides is discussed, and it is found that the dioxide is the most stable oxide for the actinides from Np onward. Our study reveals a strong link between preferred oxidation number and degree of localization which is confirmed by comparing to the ground-state configurations of the corresponding lanthanide oxides. The ionic nature of the actinide oxides emerges from the fact that only those compounds will form where the calculated ground-state valency agrees with the nominal valency expected from a simple charge counting.

Electronic structure and ionicity of actinide oxides from first principles

Self-irradiation effects in americium oxides

This chapter presents a comprehensive review of the physicochemical properties of actinide carbides. It analyzes the different metal–carbon systems one by one, starting from the temperature versus composition phase diagram. The most important ternary systems, including oxide- and nitride-carbides, are also reviewed. Known physical and chemical properties of the single compounds are presented, from the structure of the matter to the thermodynamic functions, and from the transport properties to the mechanical and optical parameters. This chapter addresses not only material features relevant to the application of actinide carbides as nuclear fuels, but also more fundamental properties of interest for basic research.

Thermodynamic and Thermophysical Properties of the Actinide Carbides

Publisher Summary At one time, a reviewer of the less-common oxidation states of the lanthanide elements would have defined these states as +2 and +4, and then covered all of their chemistry. A modern article with this brief could hardly be kept to a manageable size, such that further restrictions are necessary. In this review, the restrictions are of two kinds. The first restriction is concerned with species that have an oxidation state of + 2 as computed from their stoichiometry in the usual way (in this article we shall always use the term “oxidation state” in this sense). Such species can be divided into two distinct groups. In this article, one concentrates our attention on di-f and tetra-f species and make no attempt to treat tri-f dipositive species, comprehensively. In Section V, one discusses the factors that affect the distribution of dipositive species between the di-f and tri-f states. However, detailed reviews of the chemistry of compounds or ions are confined to di-f systems only.

J.A. Fahey

Papers

On the californium oxide system

The preparation, crystal structures and some properties of californium oxysulfate and oxysulfide