Chalcogenide Tellurides

All three elements combine readily with most metals and many non-metals to form binary chalcogenides. Indeed, selenides and tellurides are the most common mineral forms of these elements (p. 748). Nonstoichiometry abounds, particularly for compounds with the transition elements (where electronegativity differences are minimal and variable valency is favoured), and many of the chalcogenides can be considered... 

Chalcogenides of Cd are similar to those of Zn and display the same duality in their structures. The sulfide and selenide are more stable in the hexagonal form whereas the telluride is more stable in the cubic form. CdS is the most important compound of cadmium and, by addition of CdSe, ZnS, HgS, etc., it yields thermally stable pigments of brilliant colours from pale yellow to deep red, while colloidal dispersions are used to colour transparent glasses. 

The structural chemistry of the actinides is often similar to that of lighter transition metals, such as Zr and Hf, and to that of the lanthanides however, the diffuse nature of the 5/ orbitals leads to some differences and specifically to interesting magnetic and electrical properties. The actinide sulfides are generally isostructural with the selenides, but not with the analogous tellurides. The binary chalcogenides of uranium and thorium have been discussed in detail [66], but the structural... 

Rare earth sulfides, selenides, and tellurides show semiconducting properties and have potential for application in thermoelectric generation. Thin film chalcogenides of various rare earths have been prepared by multisource evaporator systems [233]. 

Similar to PbSe, the controlled growth of lead telluride, PbTe, on (111) InP was demonstrated from aqueous, acidic solutions of Pb(II) and Cd(II) nitrate salts and tellurite, at room temperature [13]. The poor epitaxy observed, due to the presence of polycrystalline material, was attributed to the existence of a large lattice mismatch between PbTe and InP (9%) compared to the PbSe/InP system (4.4%). The characterization techniques revealed the absence of planar defects in the PbTe structure, like stacking faults or microtwins, in contrast to II-VI chalcogenides like CdSe. This was related to electronic and structural anomalies. 

Sulphides. The partially ionic alkali metal sulphides Me2S have the anti-fluorite-type structure (each Me surrounded by a tetrahedron of S, and each S atom surrounded by a cube of Me). The NaCl-structure type (6/6 coordination) is adopted by several mono-sulphides (alkaline earth, rare earth metals), whereas for instance the cubic ZnS-type structure (coordination 4/4) is observed in BeS, ZnS, CdS, HgS, etc. The hexagonal NiAs-type structure, the characteristics of which are described in 7.4.2.4.2, is observed in several mono-sulphides (and mono-selenides and tellurides) of the first-row transition metals the related Cdl2 (NiAs defect-derivative) type is formed by various di-chalcogenides. Pyrite (cP 12-FeS2 type see in 7.4.3.13 its description, and a comparison with the NaCl type) and marcasite oP6-FeS2 are structural types frequently observed in several sulphides containing the S2 unit. 

However, for chalcogenide compounds (metal sulfides, selenides and tellurides etc.) the potential across the compact layer is determined by the concentration of hydrated chalcogenide ions so that the flat band potential does not necessarily depend on pH. 

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