Rare chalcogenides

C5. Craven, W. E., "Intercalation of the Rare Earth Elements into Graphite and Di-chalcogenides, M. S. Thesis, U S Air Force Institute of Technology, Air University, 1965, 68 pp. Wright-Patterson Air Force Base, Ohio. 

Assoud A, Soherinia N, Kleinke H (2007) Thermoelectric properties of the new teUurides SrSc2Tc4and BaSc2Te4 in comparison to BaY2Tc4. IntermetaUics 15 371-376 Wu P, Ibers JA (1995) Quaternary chalcogenides containing a rare earth and an alkali- or alkaMne-earth metal. J Alloy Compd 229 206-215... 

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]. 

K. Mitchell, J. A. Ibers, Rare-erath transition-metal chalcogenides. Chem. Rev. 102 (2002) 1929. 

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. 

The synthesis of chalcogenides such as those of the rare earth elements has traditionally been performed through the reaction of rare earth metals or oxides with a molten or vaporous chalcogen source in a high-temperature environment. Soft synthetic methods utilizing lower temperature conditions, such as hydrothermal or flux syntheses, can allow access also to thermodynamically metastable phases. Flux syntheses of R chalcogenides via an alkali poly-chalcogenide flux have been shown to be extremely versatile for the preparation of many new structures, some of which cannot be obtained by direct synthesis from the elements. 

From the divalent chalcogenides the trend continues as expected, through the cyclopentadienide, which has been shown to be ionic in the case of other rare earths, alkaline earths and even manganese (II), through the chloride, the hydroxide (which is a strong base comparable to calcium hydroxide), and finally to the highly ionic sulfate. 

A. A. Eliseev and G.M. Kuzmichyeva, Phase equilibrium and crystal chemistry in ternary rare earth systems with chalcogenide elements 191... 

O. Vogt and K. Mattenberger, Magnetic measurements on rare earth and actinide monopnictides and mono-chalcogenides 301... 

Yu. S. Tver yanovich and A. Tverjanovich, Rare-earth Doped Chalcogenide Glass... 

In spite of such limitations, ceramic techniques have been widely used for the synthesis of solid materials. Mention must be made, among others, of the use of this technique for the synthesis of rare earth mono-chalcogenides such as SmS and SmSe. The method involves heating the elements, first at lower temperatures (870-1170 K) in evacuated silica tubes the contents are then homogenized, sealed in tantalum tubes and heated to around 2300 K by passing a high current through the tube [15]. 

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