Cerium Kondo state

Trivalent intermetaUic [Xe]4f ytterbium compounds are particularly important for comparison with cerium compounds, since they exhibit the f-hole analog of [Xe]4f cerium. In principle, the Kondo effect should be symmetrical between electrons and holes. The maia mechanism determining the ground-state behavior in cerium and ytterbium intermetaUics is the interaction between the 4f electrons and s, p and d electrons of neighboming ligands. This so-called f—spd hybridization tends to reduce the 4f-level... 

Knowing the excitation spectrum one can compute the thermodynamic properties. In the local-moment regime they exhibit low-temperature T 7 ) Kondo anomalies that are due to the resonance states. For example, the static magnetic susceptibilty x(T), the specific heat, various transport coefficients and also dynamical quantities (photoemission spectra, dynamical structure function for neutron scattering) have been calculated (Bickers et al. 1985, Cox et al. 1986). An excellent model system for comparison with experimental data are the dilute (La, Ce)Bg alloys because of a fourfold degenerate Fg ground state of cerium (Zirngiebl et al. 1984). 

Edelstein (1968, 1970) has adopted the Coqblin-Blandin model for cerium but with an emphasis on the effect of spin compensation. This point of view was that the decrease or loss of the magnetic moment in a-Ce and the slightly decreased moments in y- and /3-Ce (based on Lock s data) was due to the antiferromagnetic polarization of conduction electrons around the 4f virtual state. Edelstein supported this idea in part by noting an apparent T dependence of the magnetic susceptibility of mixed phase cerium samples above 13 K (Lock, 1957). This temperature dependence had been suggested by Anderson (1967) for the spin compensation contribution to the susceptibility for Kondo alloys. However, subsequent susceptibility measurements of single phase a-Ce (see... 

This chapter intends to remind the reader briefly of some important aspects of the shell structure, relativistic effects, and electron correlation effects for lanthanide and actinide atoms and molecules, mainly using the example of Ce and Th. It then turns to a discussion of the electronic structure of cerium-bis( 7 -cyclooctatetraene), cerocene, which fascinated this author for more than two decades, as well as a related cerium(III)-based molecular Kondo system, i.e., bis(r7 -pentalene)cerium. These systems feature many problems of an accurate relativistic correlated description of their electronic structure and moreover leave plenty of room for alternative interpretations of their electronic ground state as well as the involvement of 4f orbitals in chemical bonding. 

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