Compounds, superconductivity chalcogenides

Five aspects of the preparation of solids can be distinguished (i) preparation of a series of compounds in order to investigate a specific property, as exemplified by a series of perovskite oxides to examine their electrical properties or by a series of spinel ferrites to screen their magnetic properties (ii) preparation of unknown members of a structurally related class of solids to extend (or extrapolate) structure-property relations, as exemplified by the synthesis of layered chalcogenides and their intercalates or derivatives of TTF-TCNQ to study their superconductivity (iii) synthesis of a new class of compounds (e.g. sialons, (Si, Al)3(0, N)4, or doped polyacetylenes), with novel structural properties (iv) preparation of known solids of prescribed specifications (crystallinity, shape, purity, etc.) as in the case of crystals of Si, III-V compounds and... 

There is currently much interest in rare-earth chalcogenides. These compounds have a great variety of properties. Some are semiconductors [1-3], others have metallic conduction [4, 5], and some become superconducting at low temperatures [6, 7]. The compounds represented by LnX and Ln2X3 (Ln is a rare-earth lanthanide and X is sulfur, selenium, or tellurium) have been investigated more thoroughly than the other compounds. 

Much of the interest in clusters of this type arises from their structural similarity to the fundamental structural element of the superconducting Chevrel phases M MogEg (M = Pb, Sn, Cu, etc.) and more recently discovered rhenium halco halide phases. Although these solid-state compounds are known only for Mo and Re, molecular MgEgLg clusters of Zr, V, Cr, Mo, W, Re, Fe, and Co have been reported (Table 2). The lone examples of octahedral zirconium- and vanadium-chalcogenide clusters are unique in that they also possess interstitial O and S atoms, respectively. Evidence for interstitial FI atoms in the clusters [Cr6Eg(PEt3)g] (E = S, Se) has been presented. ... 

Chevrel, R. Sergent, M. (1982). Chemistry and Structure of Ternary Molybdenum Chalcogenides. in Topics in Current Physics "Superconductivity in Ternary Compounds 1" Vol. 32, 5 - 86. Editors 0. Fischer and M.B. Maple. Berlin Springer. 

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