Sc, Y, La-Lu. Rare earth elements. Vol. C 9. 8. rev. ed.

The volume 'Rare Earth Elements' C 9 deals with the rare earth selenides, oxide selenides, selenites, and selenates, as well as the associated alkali double compounds, diselenate nitrates, and the selenide halides. Gaseous and matrix-isolated selenide molecules are described in the first section. The subsequent sections deal mainly with the chemical and physical properties of solid selenides of which EuSe and TmSe play the most important role. EuSe reveals a very complex magnetic behavior, the extent of which is not settled even now, despite extensive magnetic investigations and additional physical studies like Raman effect, nuclear magnetic resonance, and modulated optical spectra. The valency of TmSe can be controlled under ambient conditions by adjusting the stoichiometry or by alloying with other rare earth monoselenides. The most extensively studied oxide selenides belong to the M2O2Se type; data on preparation and crystallographic properties dominate this section. Main topics of the sections on selenites, selenates, and associated alkali double compounds are the preparation of the compounds and their thermal decomposition. The selenide halides, especially the selenide fluorides of the type MSeF, show very interesting crystallographic properties. Main topics of this section are the polytypes of YSeF. (orig./GSCH)