Monochalcogenide systems

Subsequent to the discussion of the intermetallic compounds we give a description of the transport properties of cerium monopnictides and monochalcogenides, which are compared with various actinide monopnictide and monochalcogenide systems. In these compoimds, which partly show a seraimetal-like behaviour, a great and... 

The monochalcogenides 43 can also theoretically exist in more than one tautomeric form an N-H tautomer 43a, a P-H tautomer 43b or an E-H tautomer 43c. Solution and solid-state studies on these compounds show that, depending upon the nature of the R substituents, either the N-H or the P-H tautomer predominates. Substituents which lead to increased basicity of the phosphorus lone-pair (e.g., R = NMe279, Pr80) have been shown to favour the formation of the P H tautomer, whereas in systems where the phosphorus lone pair is less basic (e.g., R = Ph81) the N-H tautomers are favoured. 

The systematics of the lattice constants of the RE monochalcogenides, see Fig. 11, indicate that the Tm ion changes its valence in going from the metallic sulfide (essentially 3+) to the semiconductor-like telluride (essentially 2+). Magnetization measurements of TmSe (48) revealed a complicated behavior, and inelastic neutron scattering studies were unable to detect the structure of the crystal field levels (49). This was unexpected because Tm is known to be a favorable element for neutron scattering, as confirmed in various studies of TmSb (50). It was therefore proposed by Wohlleben and Coles (4) that TmSe, like TmTe under pressure, is a homogeneous mixed valence system. 

Uranium monochalcogenides. These compounds are all simple ferromagnets. It is reasonable to assume that the muon takes up the (i, j) interstitial position since the same crystal structure prevails and since the lattice constants are not significantly different. As pointed out above, the local field will not cancel at such a high-symmetry site for FM order. The contact field remains, pointing in the direction of spontaneous magnetization. UTe, US and the pseudo-binary system Ui-xUa S were studied by (xSR. 

Although several concentrated alloys and compounds of Sm (notably the Sm monochalcogenides and SmB ) have been studied in connection with valence fluctuation phenomena, there is only one dilute alloy system reported to date containing Sm impurities which exhibits Kondo-like behavior. 

In order to answer the second question above, we compare the magnetic phase diagrams of two systems, EUj.Sri j.O and EUj.Sri S (see also Westerholt et al. 1977), displayed in fig. 3. Both insulating systems are based upon a ferromagnet, EuO (Tg = 69K) and EuS (7,. = 16.6 K), and are magnetically diluted with Sr. These two Eu-monochalcogenides are rather similar chemically, and crystallize in... 

Reason (b), which was the driving scientific reason for studying these systems is now recognized to be much more complex. Divalent uranium or other actinide species are almost impossible to stabilize, and so are not expected. Numerous studies, see the reviews byS choenes (1984), Brooks et al. (1984), and Baer (1984), have shown that all the monopnictides and monochalcogenides (and thus all the solid solutions as well) are essentially semimetals. It is generally accepted that the monopnictides are... 

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