Actinides physical properties

L. Manes (ed.) Structure and Bonding, Vol. 59/60, Actinides — Chemistry and Physical Properties, Springer, Berlin, 1985, 305 pp. 

Fournier JM, (1985) Actinide Solids. 5f Dependence of Physical Properties. 59160 1-56 Fournier JM, Manes L (1985) Magnetic Properties of Actinide Solids. 59160 127-196 Fraga S, Valdemoro C (1968) Quantum Chemical Studies on the Submolecular Structure of the Nucleic Acids. 4 1-62 Frasinski LJ, see Codling K (1996) 85 1-26... 

Apart from d- and 4f-based magnetic systems, the physical properties of actinides can be classified to be intermediate between the lanthanides and d-electron metals. 5f-electron states form bands whose width lies in between those of d- and 4f-electron states. On the other hand, the spin-orbit interaction increases as a function of atomic number and is the largest for actinides. Therefore, one can see direct similarity between the light actinides, up to plutonium, and the transition metals on one side, and the heavy actinides and 4f elements on the other side. In general, the presence or absence of magnetic order in actinides depends on the shortest distance between 5f atoms (Hill limit). 

Berkelium is a metallic element located in group 11 (IB) of the transuranic subseries of the actinide series. Berkelium is located just below the rare-earth metal terbium in the lanthanide series of the periodic table. Therefore, it has many chemical and physical properties similar to terbium ( Tb). Its isotopes are very reactive and are not found in nature. Only small amounts have been artificially produced in particle accelerators and by alpha and beta decay. 

The first actinide metals to be prepared were those of the three members of the actinide series present in nature in macro amounts, namely, thorium (Th), protactinium (Pa), and uranium (U). Until the discovery of neptunium (Np) and plutonium (Pu) and the subsequent manufacture of milligram amounts of these metals during the hectic World War II years (i.e., the early 1940s), no other actinide element was known. The demand for Pu metal for military purposes resulted in rapid development of preparative methods and considerable study of the chemical and physical properties of the other actinide metals in order to obtain basic knowledge of these unusual metallic elements. 

All subsequent preparations of Cf metal have used the method of choice, that is, reduction of californium oxide by La metal and deposition of the vaporized Cf metal (Section II,B) on a Ta collector 10, 30, 32, 45, 91, 97, 120). The apparatus used in this work is pictured schematically in Fig. 16. Complete analysis of Cf metal for cationic and anionic impurities has not been obtained due to the small (milligram) scale of the metal preparations to date. Since Cf is the element of highest atomic number available for measurement of its bulk properties in the metallic state, accurate measurement of its physical properties is important for predicting those of the still heavier actinides. Therefore, further studies of the metallic state of californium are necessary. 

Table XI gives the room-temperature, atmospheric pressure crystal structures, densities, and atomic volumes, along with the melting points and standard enthalpies of vaporization (cohesive energies), for the actinide metals. These particular physical properties have been chosen as those of concern to the preparative chemist who wishes to prepare an actinide metal and then characterize it via X-ray powder diffraction. The numerical values have been selected from the literature by the authors.

Considerations on the crystal structures and other physical properties of the light actinides have triggered a large effort in quantum calculations for the wave functions of the outer electrons of actinides, including in atoms as well as in solids. 

Contrary to the lanthanide metals, at least in the first half of the series, the conduction band of the actinide metals (bonding band of the metal) will be very complex. It will consist of 6 d, 7 s and 5 f admixtures. The physical properties, even the magnetic ones will be determined by this complex conduction band. 

The f-f overlapping in light actinides may cause broadening of the 5 f wave functions into 5 f bands. On the other hand, from Am on, this overlapping having decreased, this effect occurs much less. It follows that physical properties which depend from 5f orbitals may be better understood, in one case, in the band Umit, in the other case, in the atomic limit. 

The physical properties of actinide metals up to Pu - including the magnetic properties-are all governed by the complicated 5f-6d-7s conduction band. 

The situation above described has important consequences in the understanding of the physical properties not only of heavy actinide metals, but also of their compounds. We can expect e.g. that the occurence of valence fluctuations should be quite common in Am, Bk and Cf compounds (to limit ourselves to the sufficiently stable isotopes) as well as in Cf metal itself ... 

Considerable progress has been possible in the determination of chemical and physical properties of actinide solids as a result of improved preparation and purification methods. 

As many physical properties of the actinide metals depend significantly on the sample purity, refining of the metals is mandatory. The choice of the refining methods is determined by the chemical reactivity of the actinide metal in the presence of the constituents of air, by high temperature reactions with crucible materials, by the specific radioactivity and the availability of the actinide elements. 

Thus, the first attempts to understanding of chemical and physical properties in the actinide series dealt with the systematic inspection, across the series, of the thermodynamic properties influenced by the cohesive energy. As well as for the structure, the variations encountered can be attributed to the participation of outer electrons in setting up the metallic bond, with the peculiar behaviour of the 5 f orbitals among them. 

This requires that the result of the simple treatments described be sustained by a critical survey of many other physical properties Unfortunately, and especially for heavier actinides, one is hampered many times by the lack of suitable experimental information. One of the merits, on the other hand, of these approaches is that they have often led to suggestions for particular decisive measurements. 

This treatment aiming to evaluate thermodynamically the orbital character of the bond in actinide metals, follows closely the general features illustrated above and has a particular value inasmuch as it is accompanied by a fairly comprehensive survey of the chemical and physical properties of actinide metals known at that time. In it, the metallic radius and the crystal structures are taken as valence indicators AH nd Tm as the bonding indicators . The metallic valence, however, is not taken as constant throughout the actinide series, but rather allowed to vary. The particular choices are justified by physical and chemical arguments, which are taken in support of the hypothesis chosen. 

---