Intermediate-valence compounds

The compounds that do not order magnetically are represented by a triangle (7 ) on a logarithmic scale because of their wide range of values (from a few degrees for the heavy-fermion compounds to a thousand for the intermediate-valence compounds). The Greek letters a, P and y in fig. 1 represent the respective allotropic phases of Ce metal for comparison. 

IV) Within this region are included all the Ce-X compounds that do not order magnetically - heavy-fermion compounds and intermediate-valence compounds. 

Sereni, J.G., G.L. Olcese, G. Krill and J.R Kappler, 1989b, in Conf. on Intermediate Valence Compounds, Brasilia, Brasil, April 3-7, unpublished. 

For the intermediate-valence compound YbCuAl, MacLaughlin et al. (1979) observed a linear relationship between and x only for temperatures above the maximum of the bulk susceptibility. For T < == 27 K, this relation was no... 

The field of Raman scattering in rare-earth intermediate-valence compounds has now reached a certain degree of maturity and understanding so that a lot of the activity has shifted to Raman and Brillouin scattering investigations of heavy-fermion compounds and high-temperature superconductors. The exciting... 

Eq. (2.56)] is determined solely by thermodynamic stability of intermediate species, which, in turn, is expressed by the equilibrium formation constant (or, alternatively, the disproportionation equilibrium constant) of the intermediate valence compound. 

The contours in scheme (6.12) denote disproportionation reactions which could proceed both at equilibrium and in kinetic conditions. The straight arrowed lines show the possibility of titanium intermediate valency compounds to deposit at the electrode surface and to form an electrochemicaly active film system. The experimental proof of such a possibility follows from the analysis of stationary polarization curve shown in Fig. 6.33. 

Heavy-fermion systems and intermediate valence compounds 295... 

In this section we will review recent ESR studies in heavy-fermion systems (HFS) and in intermediate-valence compounds (IVC). We try to document that ESR results yield... 

The second half of this review deals with newly developed branches of solid state physics. Here it is evident that ESR made major contributions to the physics of electronically highly correlated systems, like heavy-fermion systems and intermediate-valence compounds. In the latter compounds it still has to be proven that the low density of states, which have been detected experimentally, results from the so-called Kondo whole and is a characteristic feature of IVCs. Certainly a further interesting area of ESR will be the study of Kondo insulators. In KI a hybridization gap, as a consequence of the interaction of the band states with the f-electron system, develops at low temperatures. In KI a non-magnetic impurity will reveal an effective spin i and, hence, one expects that non-magnetic impurities become ESR active below a characteristic temperature. So far we are not aware of any ESR experiments of that type in Kondo insulators. 

Electron-spin resonance (ESR) is an extremely useful tool for probing the localized magnetic moment in a variety of materials. The chapter (162) by Elschner and Loidl focuses on metallic lanthanide systems, reviewing both the classical ESR behaviors and the role of ESR in newly developed branches of solid-state physics. The former includes the determination of the site symmetry of the ESR probe and measurement of the crystal field (CF) and how it (CF) differs in metallic systems from that in insulators. The latter deals with Van Vleck systems, spin glasses, Kondo systems, heavy-fermion and intermediate-valence compounds, and high-temperature superconductors. 

L absorption edges of Ce and Yb intermediate valence compounds Non-existence of tetravalent cerium compounds, in Valence Fluctuations in Solids, eds L.M. Falicov, W. Hanke and M.B. Maple (North-HoUand, Amsterdam) p. 417. 

Very little is known about the actual magnetic properties of these intermediate-valence compounds. 

CeN is a golden material in which the 4f level is pinned at the Fermi energy, so that it is considered as an intermediate-valence compound at low temperatures (Baer and Ziiricher 1977). Above room temperature there is a progressive localization of the 4f shell, and CeN becomes trivalent at very high temperatures (T > 1200 K). The... 

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