Samarium compounds valence

For a higher conductivity, cerium dioxide can be doped either with gadolinium Cei cGd (02 or with samarium Cex jSmj02 doped cerias are quite stable chemicdly. In solid oxide fuel cells they lack the effect of interactions between the electrolyte and the cathode materials that would lead to the formation of poorly conducting compounds. However, doped cerias have an important defect in that at low oxygen partial pressures (such as those existing close to the anode) they develop a marked electronic conduction. This is entirely inadmissible for the electrolyte, as it leads to internal self-discharge currents and even to a complete internal short circuit. The electronic conduction comes about when Ce" ions in the lattice are partly reduced to Ce " ions, which creates the possibility for electrons to hop between ions of different valency. 

Closely related to the heavy fermions and spin fluctuators are the valence fluctuation/intermediate valence materials. The origin of this phenomenon starts with cerium and its a 7 transformation (see sections 3.3.4 and 3.7.2). Today it involves many cerium materials and also compounds of samarium, europium, thulium and ytterbium. Because of the breadth of the subject matter and space limitations in this chapter we refer the reader to the following reviews Jayaraman (1979), Lawrence et d. (1981), de Chatel (1982), Coqblin (1982), Nowik (1983), Brandt and Moshchalkov (1984), Varma (1985) and Stassis (1986). 

Today the lanthanide eontraction is still one of the most important tools available to the scientist in applying systematics to the behavior of lanthanide materials. Deviations from the lanthanide contraction established for a given compound series gives a measure of anomalous valences for cerium, samarium, europiun, thulium and ytterbium (see section 3.2) which are important in evaluating the nature of these elements in valence fluctuation, heavy fermion, and spin fluctuation behaviors (see section 4.4.4). 

Leger etal. (1980,1981) have described the preparation, at high pressures, of the metallic monoxides for the elements from lanthanum to samarium and have determined their structure and conductivities. A negative PAV term in the free-energy expression makes it possible to synthesize the monoxides from a mixture of the metal and the sesquioxide under pressure. These monoxides can be maintained at normal pressures after,preparation. The monoxides through NdO are metallic, golden-yellow compounds with the Ln atom being trivalent. SmO is metallic with a valence close to... 

The binuclear samarium and ytterbium complexes with mixed valence of Ln(II, IQ) (Me5C5)2Sm( i-Cp)Sm(C5Me5)2 [37] and (Me5C5)2Yb(ji-F)Yb(C5Me5)2 [46], are close to the being considered class of compounds in their nature. The complex with cyclopentadienyl bridge can be isolated from the mixture containing cyclopentadiene and... 

Lanthanide atoms are known to most likely exist in halogen compounds in a stable trivalent state. The thermodynamics of vaporization of LnX3 was recently studied fairly completely [1-4], Europium, ytterbium, and samarium are exceptions for which reliable thermodynamic characteristics of the vaporization process have virtually not been published. This primarily accounts for the incongruent character of evaporation [5,6] and the valence transformation Ln(III) Ln(II) in these compounds at high temperatures, which is in accord with the general tendency toward decreasing stability of the trivalent state in the lanthanide series [7, 8] La, Lu, Gd, Ce, Tb, Pr, Er, Nd, Ho, Pm, Dy, Tm, Sm, Yb, and Eu. Their thermal decomposition occurs due to the decreased stability of the state of Ln(III) in tribalogenide compounds [1] ... 

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