Europium monochalcogenides

The extensive NMR work on the rare-earth pnictides (RN, RP, etc.) was reviewed in section 2.2.3 and 2.2.3.2. Various of the rare-earth chal-cogenides (oxides, sulfides, etc.) also form in the cubic rock-salt structure, in particular those of Eu and Sm. The europium monochalcogenides are semiconducting magnetic materials whose properties have been reviewed by Wachter (1972) also see ch. 19. Both NGR and NMR methods afford opportunity to study these compounds, and the work on oxides has been reviewed in the fore-going section (section 2.3.3). Table 18.24 provides a brief summary listing of experimental work. 

Most monochalcogenides of the Group 3 metals adopt the rock salt (NaCl) structure. Note that the crystal chemistry of divalent europium is very similar to that of the alkaline earths, particularly strontium, as the radius of Eu is almost the same as that of Sr ". For the Yb compounds, the cell dimensions are practically identical with those of the Ca compounds. 

Rare-earth monochalcogenides are trivalent in the ground state and have metal-type conduction. These compounds, particularly the monosulfides, are highly stable in the thermal sense [8j. They melt without decomposing. For example, the vapor of lanthanum monosulfide consists mainly of LaS molecules [9]. Europium, ytterbium, and samarium monochalcogenides are semiconductors. All the monochalcogenides have the NaCl-type structure. 

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