Molybdenum Chevrel phases

Fig. 6.1 The fundamental structural unit found in the Chevrel phases (cluster MoeXg full circles Mo atoms) displayed in three ways to emphasize different views of the connectivity. In (a) an octahedron of molybdenums (Mo-Mo = 2.7 A) is encased in a cube of chalcogens (Mo-S 2.45 or Mo-Se 2.6 A). Scheme (b) exhibits the same cluster as consisting of an octahedron with its triangular faces capped by chalcogenides. In (c), the cluster has been reoriented so that a threefold axis is vertical. (Reproduced from [10])...

The situation is very similar in the Chevrel phases. These are ternary molybdenum chalcogenides A,.[Mo6Xg] (A = metal, X = S, Se) that have attracted much attention because of their physical properties, especially as superconductors. The parent compound is PbMo6Sg it contains Mo6Sg clusters that are linked with each other in such a way that the free coordination sites of one cluster are occupied by sulfur atoms of adjacent clusters (Fig. 13.9). The electric properties of Chevrel phases depend on the number of valence electrons. With 24 electrons per cluster (one electron pair for each edge of the... 

R. E. McCarley No, we have done very little work along this line, although I think important results will be obtained from studies of mixed 0, S phases. So far we have found no direct structural analogies between the reduced ternary molybdenum oxide phases and the various ternary sulfide or selenide phases of the Chevrel type. 

In passing, it should be noted that Michel and Raveau had carried out electrical measurements on several alkaline-earth substituted La2Cu04 compounds and presented (140) their experimental results in a comprehensive review during 1984. Their work, however, was primarily structural with a focus on electrical and magnetic properties above 50 K for this reason they missed observing the superconducting transition at 30 K. It is this author s belief that these Cu-O phases should be called the "Raveau-Michel" phases in much the same way as the molybdenum sulfide superconductors are called the "Chevrel" phases. 

Chevrel Phases Ternary molybdenum chalcogenides, M Mo X, are polynuclear clusters of special... 

H.-L.Luo Thin-Film Ternary Superconductors. - H.Nohl, W.Klose, O.K Andersen Band Structures of MxMogXg- and M2Mo6X6-Cluster Compounds. - S.D. Bader, S.K.Sinha, B.P.Schweiss, B.Renker Phonons in Ternary Molybdenum Chalcogenide Superconductors. -F.Pobell, D. Rainer, H. Wiihl Electron-Phonon Interaction in Chevrel-Phase Compounds. - Subject Index. 

A class of metal cluster superconductors of particular Interest consists of ternary molybdenum chalcogenides, conmonly known as the Chevrel phases (13). These phases were the first type of superconducting ternary system found to have relatively high critical temperatures and exhibited the highest known critical magnetic fields (Hc2 before discovery of the copper oxide... 

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