STRUCTURAL AND THERMODYNAMIC PROPERTIES OF ACTINIDE SOLIDS AND THEIR RELATION TO BONDING
The problem of bonding in actinide solids has been approached through the establishment of semi-theoretical correlations between thermodynamic and structural properties and the degree of participation to the bond of the different electronic orbitals of the actinide atom. The first part of the chapter is devoted to an analysis of these correlations, as well as to the presentation of the most important experimental results. In a second part the following stage of development is reviewed, i.e. the introduction of more quantitative theories mostly based on bond structure calculations. These theories are given a thermodynamic form (equation of states at zero temperature), and explain the typical behaviour of such ground state properties as cohesive energies, atomic volumes, and bulk moduli across the series. They employ in their simplest form the Friedel model extended from the d- to the 5f itinerant state. The Mott transition (between plutonium and americium metals) finds a good justification within this frame. In actinide binary compounds an equation of state can also be developed on the same lines. The difference in electronegativity of the actinide and the non-actinide element plays an important role, determining the degree of mixing between the actinide orbitals (5f and 6d) and the orbitals of the ligand. A mixture of metallic, ionic and covalent bond is then encountered. In the chapter, two classes of actinide compounds are reviewed: NaCl structure pnictides or chalcogenides, and oxides. In oxides a large departure from the stoichiometric composition is usually met. The importance of this phenomenon, also for the understanding of the oxide bond, is highlighted at the end of the chapter.
Bibliographic Reference: PUBLISHED IN STRUCTURE AND BONDING, NO. 59/60, PP. 75-126, EDITED BY SPRINGER-VERLAG, 1985
Record Number: 1989123053200 / Last updated on: 1987-01-01
Available languages: en