Using Correlations to Understand Changes in Actinide Bonding
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Using Correlations to Understand Changes in Actinide Bonding Richard G. Haire1 and Stephen Heathman2,3 1 CSD, Oak Ridge National Laboratory, P. O. Box 2008, Oak Ridge, TN, 37831-63756 2 Joint Research Center, ITU, EC, Karlsruhe, D76125, Germany 3 ITU, Karlsruhe, D76125, Germany Category: Properties and characterization of actinide materials Keywords: Bonding; electronic nature; roles of f-electrons ABSTRACT An important issue in actinide science is the changing role of the 5f electrons, both when progressing across the series, as well as how experimental variables affect these roles in a particular element’s chemistries and physics. The function of these 5f electrons can be changed by experimental conditions: temperature and pressure being two of many such variables. The 5f electrons of several actinide metals, their alloys and compounds are affected greatly by pressure, due to the very large decreases in interatomic distances encountered under pressure. The latter bring about significant changes in the total energy of the system and in the electronic energy levels, which in turn affect the potential for overlap/hybridization) of their orbitals, promotion of electrons to other orbitals, etc. The physical state, temperature, pressure, specific structures, magnetic interactions and spin polarization effects are all critical parameters for bonding. Often correlations of behavior with these parameters can provide unique insights and understanding into the bonding and the changes that occur in it. With the advancement of modern computation approaches using FPMTO, or other approaches, theory has enlightened greatly the understanding of not only the bonding behavior of these elements but also the understanding of changes observed experimentally. But these computational efforts have some complications and limitations, and at times experimental findings and theory are not always in full agreement. In contrast to the behaviors of the elements, changes observed with compounds often are not linked directly to the involvement of 5f electrons, due in part to the presence and bonding role of nonactinide atoms. The latter affect both the actinide interatomic distances and the type of electronic orbtals that interact. Presented here is an overview of the pressure behavior several actinide elements, some insights into the bonding behavior of compounds under pressure and selected correlations that help explain changes occurring in electronic configurations and bonding.
INTRODUCTION It is well recognized that at atmospheric pressure and 273 K the actinide elements exhibit much greater variation in bonding behavior than elements in the 4f-electron, sister series. The bonding in the actinide elements varies from having itinerant 5f electrons, to non-5f-electron bonding members having three or two bonding electrons. Not only do the atomic volumes vary widely across the series but a large variation in crystal structures, at times with complex symmetries, is observed. Thorium is also unique, and its structure appears more re
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