Electrical cerium compounds

Structural transition has a drastic effect on the electrical behavior of these indides (abrupt change in the slope), but no observable effect on the magnetic data (table 20). The samarium and ytterbium compoimd show non-Ciuie-Weiss behavior. Specific heat data revealed a high y coefficient of 130 mJ/molK for the cerium compound (Pleger et al., 1987). 

Much less efforts have been put in the study of the cerium monochalcogenides CeY (Y = S, Se and Te), since they were considered as rare examples of cerium compounds with normal behaviour. However, the first resistivity measurements on CeS (Schoenes and Hulliger 1985) displayed a temperature dependence similar to that found in CeAl2- This prompted a more systematic investigation of the electrical resistivity of CeS, CeSe and CeTe on single crystals in a large temperature region (2 to 1000 K). 

The use of electricity in reactions is clean and, at least in some cases, can produce no waste. Toxic heavy metal ions need not be involved in the reaction. Hazardous or expensive reagents, if needed, can be generated in situ where contact with them will not occur. The actual oxidant is used in catalytic amounts, with its reduced form being reoxidized continuously by the electricity. In this way, 1 mol% of ruthenium(III) chloride can be used in aqueous sodium chloride to oxidize benzyl alcohol to benzaldehyde at 25°C in 80% yield. The benzaldehyde can, in turn, be oxidized to benzoic acid by the same system in 90% yield.289 The actual oxidant is ruthenium tetroxide. Naphthalene can be oxidized to naphthoquinone with 98% selectivity using a small amount of cerium salt in aqueous methanesulfonic acid when the cerium(III) that forms is reoxidized to cerium(IV) electrically.290 Substituted aromatic compounds can be oxidized to the corresponding phenols electrically with a platinum electrode in trifluoroacetic acid, tri-ethylamine, and methylene chloride.291 With ethyl benzoate, the product is a mixture of 44 34 22 o/m/fhhy-... 

To determine manganese valency, the method previously described by Bloom et al. [1] is employed. As it uses the ability of Fe2+ ions to reduce Mn3+ and Mn + in Mn + ions, it may not be employed for cerium and copper containing compounds as long as the valencies of these ions in the sample are not determined. Owing to the determination of Mn + content it is then possible, using electrical neutrality equations, to find the value of the non-stoichiometry in oxygen 1. 

Kondo-like behavior was observed in the lanthanide compoimds, typically in Ce and Yb compounds (Buschow et al. 1971, Parks 1977, Falicov et al. 1981). For example, fire electric resistivity in Cej Laj j Cu6 increases logarithmically with decreasing temperature for all the Af-values (Sumiyama et al. 1986), as shown in fig. 1. The Kondo effect occurs independently at each cerium site even in a dense system. Therefore, this phenomenon was called the dense Kondo effect. 

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