5f localization

The Mott-like transition, a central concept for the description of the actinide metal series, causes the sudden increase of the atomic volumes, encountered when between Pu and Am (Fig. 3). All other properties indicate the onset of a 5f localized behaviour at Am (see Part V) the 5 f pressure, which had contained to smaller values the equilibrium interactinide distance, suddenly gives in, with the withdrawal of the 5f s within the atomic core. The occurrence of such a transition within a series characterized by an unsaturated shell, is a unique phenomenon of the actinide series. In lanthanides, it does not occur except perhaps under pressure in cerium metal the approaching of cerium atoms induces suddenly the itineracy of 4f orbitals and a sudden volume collapse - see Chap. C. Neither it occurs in d-transition metal series, where the atomic volumes have an almost parabolic behaviour when plotted vs. Z (see Fig. 3 and Chap. C). The current... 

After a survey of the basic theory and some experimental aspects of photoelectron spectroscopy which are relevant to actinide solids, two systems are illustrated elemental actinide metals, in which the Mott transition between plutonium and americium is evidenced in a photographic way by photoemission, and strongly ionic oxides, in which the 5f localized behaviour is clearly seen, and indications of f-p or d-p covalent mixing are investigated. 

Although only one valence electron resides in a 5f-localized orbital on uranium in [U(C7H7)2], a formal oxidation state of -1-3 (5f ) was assigned, based on the fact that the HOMO Se molecular orbitals (occupied by four electrons) are nearly 50% 5f in character, and so two of these electrons were assigned to the metal. EPR and electron-nuclear double resonance (ENDOR) studies of [(C7H7)2U] suggest that the complex could be treated as 5f, with a ground-state molecular orbital comprised of both 5br and 5f(r orbitals. ... 

Similar to hydrogen also the addition of boron can be used to stimulate the expansion of the crystal lattice with a consequent 5f localization. This effect was illustrated in the system UB4-YB4, where magnetic order appears at intermediate concentrations, while both terminal phases are paramagnetic. In UB4 this is due to 5f-5f overlap and a considerable delocalization, whereas a weakening of the interatomic exchange interactions between the localized U-moments play a role for low U concentrations (Wallash et al. 1987 and further references quoted therein). 

Here x (q, co) and the single ion dynamical susceptibility u( >) are tensors in both sublattice (A, B) and transverse xy) Cartesian coordinates. The poles of eq. (84) determine the collective excitations of 5f-local moments. In the paramagnetic phase they are given by the magnetic exciton dispersion... 

Naegele JR, Ghijsen J (1985) Localization and Hybridization of 5f States in the Metallic and Ionic Bond as Investigated by Photoelectron Spectroscopy. 59160 197-262 Nag K, Bose SN (1985) Chemistry of Tetra-and Pentavalent Chromium. 63 153-197 Naletvajski RE (1993) The Hardness Based Molecular Charge Sensitivities and Their Use in the Theory of Chemical Reactivity. 80 115-186 Natan MJ, see Hoffman BM (1991) 75 85-108 Neilands JB, see Liu A (1984) 58 97-106 Neilands JB, see Chimiak A (1984) 58 89-96... 

Naegele, J. R., Ghijsen, J. Localization and Hybridization of 5f States in the Metallic and Ionic Bond as Investigated by Photoelectron Spectroscopy. Vol. 59/60, pp. 197-262. 

In this paper, we report MCP of Use and UTe which have been carried out at AR-NE1 station of KEK, Japan, and try to separate the spin and orbital contributions of magnetic moments by combining MCP with the magnetization measurement. Furthermore, we discuss the degree of localization of 5f electrons of these samples by decomposing the MCP into localized component and itinerant component. 

The spin moments were decomposed into localized 5f component, ps(5f), and diffused components, ps(diff). Combining magnetization measurement with this decomposition, the orbital contribution, pL(5f), has been deduced. ... 

Armed with the general concepts developed in the previous section, we proceed now to the experimental evidence of 5f itinerant vs. localized behaviour in actinide metals. 

Whereas there are experimental evidences for the band behaviour of 5 f electrons up to plutonium (Z = 94) (see Table 3), the same criteria show that suddenly americium (Z = 95) behaves like a normal lanthanide having well localized 5f electrons ( and Chap. C) ... 

It can be stated that up to plutonium, 5 f electrons are in the conduction band and have no magnetic moment from americium on, 5f electrons are localized and carry a magnetic moment. 

Thus, although it is safe to assume that the 5f states are localized states, excited f states are never far above the Fermi energy. They will, therefore, influence the electronic properties and high temperature phases of Cf and Es (which, with a metal radius R = 2.0 A seem to have attained divalency). 

No Hill plots can be drawn for transplutonium compounds for obvious reasons very few are known, Am compounds are essentially non-magnetic (J = 0) and all known results suggest well localized 5f states. 

In Chap. E, photoelectron spectroscopic methods, in recent times more and more employed to the study of actinide solids, are reviewed. Results on metals and on oxides, which are representative of two types of bonds, the metallic and ionic, opposite with respect to the problem itineracy vs. localization of 5f states, are discussed. In metals photoemission gives a photographic picture of the Mott transition between Pu and Am. In oxides, the use of photoelectron spectroscopy (direct and inverse photoemission) permits a measurement of the intra-atomic Coulomb interaction energy Uh. 

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