Cerium electron system

The electronic specific heat coefficient, y, is proportional to the DOSs at the Fermi level. In general, in pure metals, it is of the order of a few mj/ mol K. Simply thinking, the electronic DOSs at the Fermi level is proportional to the effective mass of conduction electrons. The most conspicuous and noticeable systems with respect to their electronic specific heat coefficients are heavy electron systems that include some actinide and cerium compounds to be mentioned later. For example, in the case of a typical heavy electron system CeCug, the electronic specific heat coefficient reaches 1.5 J/mol K, which is more than 1000 times larger than that of a normal metal (Satoh et al., 1989). 

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. 

Similar MMCT transitions occur for phases in certain systems Lu203-M(IV)02. As early as 1915 the name Ceruranblau (cerium-uranium blue) was given to a dark blue phase with approximate composition 2Ce02 UO2 [76]. The electron exchange equilibrium seems to be [6,77] U(IV) -H Ce(IV) < U(V) Ce(III). 

In subsequent studies, methyl vinyl ketone (2.0 mmole) was chosen as the dienophile so as to determine the combined effect of the ionic liquid (2 mL) and the Lewis acids (0.2 and 0.5 wt%) upon the yield and selectivity. Without the Lewis acid catalyst, this system demonstrated a 52% conversion of the cyclopentadiene (2.2 mmol) in 1 h with the endojexo selectivity being 85/15. The cerium triflate-catalyzed reaction was quantitative in 5 min and the endo. exo selectivity was very good for this experiment as well (94 6, endo. exo). Also with the scandium or yttrium salts tested, reactions came to completion in a short time with high stereo-selection. Cerium, scandium and yttrium triflates are strong Lewis acids known to be quite effective catalysts in the cycloadditions of cyclopentadiene with acyclic aldehydes, ketones, quinones and cycloalkenones. These compounds are expected to act as strong Lewis acids because of their hard character and the electron-withdrawing triflate group. On the other hand, reaction times of 1 hour were required for... 

Lanthanum-138 decays to 138Ba by electron capture (66%) and to 138Ce by (3-decay (34%). Lanthanum and cerium are REEs, whereas barium is an alkaline-earth element like calcium and strontium. Both systems have been studied as potential chronometers but are not in... 

Perhaps the earliest system to be described as an Anderson transition was cerium sulphide (Cutler and Mott (1969), on the basis of observations by Cutler and Leavy (1964)). The material in question can be written Ce3 xvxS4, where v is a cerium vacancy, the vacancies being distributed at random. The field near a cerium vacancy repels electrons, because they are negatively charged. Variation of x, then, changes the number of electrons and the number of scatterers. Figure 1.25 shows some results on the conductivity. At that time the present author believed... 

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