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Połączenia lantanowców z niewspółmiernymi strukturami warstwowymi

Palewski T.

Wiadomości Chemiczne

2003

[Z] 57, 9-10

827--854

In a family of sulfide and selenide compounds are known composite crystals with incommensurate layered crystal structure and with a general formula (MX)1+n(TX2)m where M = Pb, Sn, Sb, Bi and rare earth metals (Ln), T = Ti, V, Cr, Nb and Ta, and X = S and Se which in the English scientific literature are called „misfits". The crystal structure of misfits consist of two types of slabs with strong intra-slab bonding and a weaker interaction between them. One type of slabs (TX2) is a three-atom-thick sandwich of a transition metal T layer between layers of chalcogenide atoms X, the second one (MX) consists of a two-atom-thick double layer of atoms each with the same number of M and X atoms. The paper presents a description of part of the whole class of misfits compounds, the rare earth misfits (LnX)1+n (TX2)m. Some physical properties of them, mainly the electrical and magnetic properties, originate from the first or the second types of slabs and may be changed independently. The Introduction gives a short history of discovery of the misfits compounds and their location in the family of composite crystals. Then details of the crystal structure of lantanide misfits have been presented, types of slabs and their geometric forms, preffered crystal structures and the direction of incommensurability. Two next parts present the way of determination of their chemical formula and methods of their synthesis. The described physical properties concern the electrical resistivity, superconductivity, magnetism, and some spectral properties. On this basis possible band structures are presented. Particular attention is devoted to the similarities and differences of the physical properties between parent compounds LnX, TX2 and the misfits (LnX)1+n (TX2)m. Finally, some perspective studies of the rare earth misfits are considered