Cerium crystal fields

Fig. 7.27. It is seen from Fig. 7.27 that the rate constant for the exchange reaction [Ce. +-Ce(EDTA)-] is much lower than the expected value. It is to be noted that the crystal field stabilization energy including spin-orbit interaction reaches a maximum for cerium in the cerium sub group and the ligand field strength is in the order H2O < CH3COO. The...

For the ethylsulphates, with only four independent terms, the equivalent crystal-field operators were derived by Elliott and Stevens (1952) and used by them to interpret the magnetic resonance results (Elliott and Stevens 1953). Only minor modifications of the numerical coefficients of the terms were needed to give a reasonable fit for each member of the series. Some further interactions are required, however, for two cerium compounds. In the hexagonal crystal field of the ethylsulphate, the energy levels of the ground manifold J = f are split into three... 

Wienand et al. (1982) worked extensively on cerium-based monopnictides. They combined temperature dependent measurements of the susceptibility, resistivity and ESR on powdered samples of RZ (R=Sc, Y, La Z = Sb, Bi) and on YAs, containing small amounts of cerium ions. In addition to the already known Ce resonances they found well-defined resonance absorptions in LaBi, YAs and YBi. The absorption lines were characteristic of a F7 groimd doublet, with g(F7)=1.42 0.02. ScSb and ScBi did not show any indications of a cerium resonance. The model of Takegahara et al. (1981), which explains the surprisingly small crystal-field splittings of some monopnictides, inspired... 

The interpretation of the low-temperature response obtained on Yb samples is clearly still complex. In low-symmetry structures the dependence on crystallographic direction implies that the crystal-field interactions must be important, although bearing in mind the physics of cerium and uranium systems discussed in sect. 4, the effects of hybridization will have to be incorporated into any comparison between theory and the neutron results. 

The role of the crystal-field interaction remain obscure in all these systems, both for actinides and cerium. Whereas in the other lanthanide NaCl-type compounds, LnX and LnZ, the easy directions are given by straightforward crystal-field considerations and the value of the crystal-field potential varies in a systematic way across the lanthanide series, this is not the case in the materials discussed here. The crystal-field energy levels can be measured in the cerium compounds with neutron inelastic scattering, but have not been observed in the uranium (or higher) actinides. It is assumed that this inability to observe directly the crystal-field levels is because they are strongly broadened by the interaction between the 5f and conduction electrons. This has been the subject of much work by Cooper and his collaborators. 

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